Cuba 09 Abstracts. Workshop "Subduction Zones of the Caribbean". Dedicated to the memory of Professor Wayne Jolly.

M.Sc. Enrique Diego Arango Arias¹, Ing. Nicolás Vega Garriga¹, Ing. Yamina Ríos Martínez¹, Ing. Eric Escobar Pérez¹, Ing. Zulima Alvarez¹

¹Centro Nacional de Investigaciones Sismológicas, Calle 17 No. 61 e/ 4 y 6, Vista Alegre, Santiago de Cuba, CP 90 400, Cuba.

La región del nordeste del extremo oriental de Cuba ha manifestado desde los años 90 del siglo pasado una actividad sísmica significativa con la ocurrencia de varias series de terremotos. Los parámetros del mecanismo focal del sismo ocurrido el 28 de diciembre de 1998 con una magnitud de 5.4 en la escala de Richter se corresponden con una falla inversa de bajo ángulo (22°) con un azimut de buzamiento de 200°. La interpretación de una red de perfiles sísmicos profundos realizados en esta zona reflejan la existencia de una falla transcortical. Coincidentemente con el trazado de esta falla, el mapa gravimétrico de Bouguer de la parte norte del Caribe manifiesta la existencia de una anomalía con mínimos negativos que continúan desde el arco de las Antillas menores y el norte de La Española.

Todas las evidencias geodinámicas, geofísicas, morfotectónicas y sismológicas permiten aseverar la continuidad al norte del extremo oriental cubano de la falla Norte de la Española, con un mecanismo predominante inverso y secundario de deslizamiento por el rumbo siniestro, que provoca un proceso de infracorrimiento mediante el cual la placa de Norteamérica choca y se introduce por debajo del bloque oriental cubano. La existencia de esta estructura tectónica explica de manera satisfactoria la génesis de la sismicidad que ocurrida al noreste de Moa. Este proceso es similar al determinado por otros autores al norte de La Española en esta misma estructura tectónica y es la responsable de la sismicidad que genera en toda la zona de norte del Caribe donde han ocurrido sismos de hasta 8.1 de magnitud Richter.

(1) Institut de Géologie et Paléontologie, Université de Lausanne, Anthropole, CH-1015 Lausanne, Switzerland. E-mail: Peter.Baumgartner@unil.ch

The breakup of Pangea has been a major concern since the early days of Plate tectonics While the opening history of the Atlantic is now very well constrained, the complex puzzle of microplates preserved in Circum-Caribbean terranes is much more difficult to resolve into a model of opening and closing of successive ocean basins, separated by microcontinents or intraoceanic arc systems. Remnants of Mesozoic Proto-Caribbean ocean crust, today preserved in subduction complexes, are scarce and their interpretation is controversial. The Proto-Caribbean geodynamic history is at least as complicated as Mesozoic Tethyan one, but there is far less field data available.

The evidence of very similar fossils on the Tethyan and the W-American side of Pangea implies an at least intermittent normal marine pathway at low latitudes through Pangea at least since the Pliensbachian. However, this evidence does not imply the existence of a trans-Pangean oceanic current system in the early-middle Juarssic.

At present, the hypothesis of a Late Juarssic – Early Cretaceous circum-global, equatorial current system flowing through the Tethayn –Atlantic – Caribbean Seaway is largely accepted and used to explain global climate changes during this time. Several groups have done modelling using a General Ocean Model. However, the plate tectonic reconstructions used are very generalized and the oceans are assumed to be of infinite depth from shoreline to shoreline. This is clearly a false assumption, since it ignores the existence of vast epicontinental shallow seas, especially in Europe and North America. These shallow seas allow the dispersal of most fossil groups, but are obstacles to a major oceanic unidirectional current system.

The sedimentary record of Tethys, the Central Atlantic and the few localities considered to represent the Proto-Caribbean speak against such a current system: Middle to Late Jurassic basinal sediments are predominantly radiolarian cherts in Tethys and the W-Pacific, while sections recovered from the Central Atlantic, the Gulf of Mexico and the Proto-Caribbean lack radiolarian cherts but contain pelagic carbonates or claystones (beneath the CCD).

An E-W directed global current system would account for the higher fertility radiolarian cherts on both extremes, but is in contradiction with the low fertility ( Nannofossil limestone) facies in the Central Atlantic. The Atlanic always was (and still is) a carbonate ocean characterized by an antiestuarine circulation until today.

By latest Jurassic times, the Western Tethys changed from radiolarite sedimentation to calcareous low-fertility facies sedimenation like the Atlantic, while in the Circum-Pacific realm radiolarite sedimentation continued. It is only by Campanian times that we can observe a global homogenisation of facies. In conclusion, the plate tectonic models need refinement especially in terms of bathymetry to enable more realistic modelling of a hypothetical circum global equatorial current system during the Jurassic-Early Cretaceous.

Luís R. Bernal⁽¹⁾, Guillermo Millán⁽¹⁾, Antonio García Casco², Angélica Isabel Llanes⁽¹⁾, Kenya Nuñez⁽¹⁾, Elieskys Piloto Lorente⁽¹⁾, Maricela Pérez Enriquez⁽³⁾, Maria de los Angeles Gómez Fernández⁽³⁾

En la región central de Cuba se distinguen dos grandes suturas, una meridional bien definida por su expresión estructural que marca el contacto entre las secuencias metamorfizadas del Escambray y las anfibolitas de Mabujina, y otra septentrional representada en un cinturón ofiolítico muy deformado que se extiende desde las inmediaciones de Rancho Veloz, al noroeste, hasta las cercanías del poblado de Florencia, al sureste. Su estructura interna es muy complicada pues las ofiolitas forman escamas que se imbrican con secuencias del arco volcánico Cretácico y del margen continental de Las Bahamas y su depresión marginal.

Como resultado de los trabajos realizados en un manto tectónico de melange serpentinítico expuesto en la región de Santa Clara se ha corroborado la presencia de bloques originados en distintos paleoambientes tectónicos los cuales aparecen englobados dentro de una matriz serpentinítica con estructura brechoide y foliada. Entre los bloques aparecen vulcanitas del arco cretácico y calizas cretácicas de la zona Placetas lo cual demuestra que el emplazamiento del melange ocurrió durante la colisión con el paleomargen de Las Bahamas en el Eoceno Medio. Sin embargo este melange incluye además numerosos bloques de metamorfitas de alta presión originadas en una zona de subducción, entre los cuales se destacan eclogitas y unos esquistos glaucofánicos de bajo grado que proceden de sedimentos de un prisma de acreción. Estos bloques de metamorfitas de alta presión fueron exhumados probablemente en el Cretácico Inferior dentro de un melange serpentinítico mas antiguo, cuya matriz son unas antigorititas densas y foliadas que a menudo se preservan, envolviendo a los bloques de metamorfitas actualmente incluidos en este manto tectónico de melange serpentinítico originado durante la colisión con el paleomargen de Las Bahamas.

Blanco-Quintero, I.F.⁽¹⁾, García-Casco, A.^(1,2), Lázaro-Calisalvo, C.⁽¹⁾, Rojas-Agramonte, Y.⁽³⁾, Vega-Rodríguez, A. ⁽⁴⁾,Núñez, K.⁽⁵⁾, Iturralde-Vinent M.⁽⁶⁾, Cascarrilla, S⁽¹⁾.

(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002-Granada, Spain.

(2) Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Fuentenueva s/n, 18002-Granada, Spain.

(3) Institut für Geowissenschaften, Universität Mainz, D-55099 Mainz, Germany.

(4) Departamento de Geología, Instituto Superior Minero-Metalúrgico, Las Coloradas s/n, 83329-Moa, Cuba.

(5) Instituto de Geología y Paleontología, Via Blanca y Carretera Central, La Habana, Cuba.

(6) Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100, Cuba.

La Corea mélange is tectonically located in between the Cretaceous volcanic arc (Santo Domingo Fm.) and the Mayari-Cristal ophiolitic massif of eastern Cuba. It consists of tectonic blocks of epidote±garnet amphibolite, greenschist, quartzite, blueschist and pegmatitic and trondhjemitic rocks within a serpentinite matrix. The most abundant rock type is epidote±garnet amphibolite that contains a peak metamorphic assemblage of pargasite, epidote, titanite, rutile ±quartz ± garnet ± phengite and apatite as accessory phases. Garnet porhyroblasts contain inclusions of epidote, phengite, chlorite and plagioclase. Retrograde chlorite, actinolite-magnesiohornblende, albite, phengite, titanite and hematite overprint the peak assemblage.

Amphibole is predominantly calcic, with (Na+K)_A in the range 0.504-0.612 for peak edenite-pargasite and 0.035-0.488 for retrograde actinolite-magnesiohornblende-tschermakite. Garnet is relatively rich in almandine (Xalm max. 0.636) and, to some extent, grossular (0.2-0.3), and poor in pyrope and spessartine (0.15-0.20 and 0.02-0.10, respectively), showing concentric zoning typical of prograde growth. Epidote group minerals include clinozoisite as the most common variety with very low pistacite contents (0.1-0.3). Phengitic mica is variable in celadonite content (Si = 6.229-6.967 apfu), with Mg# (0.615-0.708). Peak metamorphic plagioclase was not found. Retrograde plagioclase is almost pure albite in composition (Xab > 0.92). Chlorite is very common and replaces amphibole and garnet.

The calculated peak P-T conditions using THEMOCALC (v. 3.31) of garnet-bearing amphibolite samples (Grt+Prg+Ep+Qtz±Ms±Pl), are 670-750 ºC, 13-15 kbar. Pre-peak conditions calculated using inclusions within garnet (Grt+Ep±Ms±Ch±Pl) are 520-540 ºC, 10-11 kbar. Retrograde conditions (actinolitic Amp+Ep+Ms±Qtz±Ab±Chl±Gl) are 400-500 ºC, 8-11 kbar. These P-T calculations indicate counter-clockwise P-T paths (Fig. 1A) and exhumation of the blocks in the mélange along a subduction channel during ongoing subduction. Some rocks followed complex trajectories (sample LC-GU-1B) suggesting P-T fluctuations during exhumation and complex fluxes of material within the subduction channel (Fig.1B).

Fig. 1. P-T diagrams showing paths calculated for garnet-bearing amphibolite blocks of the La Corea mélange, eastern Cuba. The grid for the basaltic system is after Vielzeuf and Schmidt, (2001).

Vielzeuf, D. & Schmidt, M. W. (2001). Melting reactions in hydrous systems revisited: applications to metapelites, metagreywackes and metabasalts. Contributions to Mineralogy and Petrology 141, 251-267.

Blanco-Quintero, I.F.⁽¹⁾, García-Casco, A.^(1,2), Rojas-Agramonte, Y.⁽³⁾, Lázaro-Calisalvo, C.⁽¹⁾, Kröner, A.⁽³⁾, Proenza, J.A.⁽⁴⁾, Manuel Iturralde-Vinent ⁽⁵⁾, Núñez, K.⁽⁶⁾, Vega-Rodríguez, A. ⁽⁷⁾

(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002-Granada, Spain

(2) Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Fuentenueva s/n, 18002-Granada, Spain

(4) Departament de Cristal.lografía, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, 08028-Barcelona, Spain

(5) Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100, Cuba.

(6) Instituto de Geología y Paleontología, Via Blanca y Carretera Central, La Habana, Cuba.

(7) Departamento de Geología, Instituto Superior Minero-Metalúrgico, Las Coloradas s/n, 83329-Moa, Cuba

The intimate association of trondhjemite and amphibolite in subduction-related tectonic blocks of the La Corea mélange, eastern Cuba, provides clues for deciphering the nature of hot, deep-seated processes that occurred during subduction of oceanic lithosphere in the Caribbean realm. The trondhjemitic blocks are exclusively associated with amphibolites and do not crosscut the serpentinitic mélange matrix, excluding their origin as magmatic arc intrusions. Their geochemical characteristics also show them not to represent oceanic plagiogranites. Wet partial melting of amphibolite is, however, consistent with field and petrological data. Free water may have been produced by dehydration of subducted serpentinite underlying the subducted oceanic crust.

Partial melting of subducted metabasite indicates anomalously high geothermal conditions (ca. 14 ºC/km) during subduction that can be conceptualized within two main tectonic scenarios: a) onset of subduction and b) subduction of young oceanic lithosphere (including a ridge). The counter-clockwise P-T paths followed by the amphibolite blocks are consistent with both scenarios, in agreement with geodynamic models for the Caribbean region that predict initiation of a SW-dipping subduction zone of young oceanic lithosphere during the Aptian.

Published age data, our new SHRIMP zircon ages for trondhjemites, and Ar/Ar ages of amphibolites and trondhjemites indicate that partial melting conditions were attained in the Aptian (ca. 115 Ma) and that exhumation within the subduction channel occurred during the late Cretaceous until ca. 73 Ma. These data are consistent with evidence from other subduction-related mélanges in Cuba (Sierra del Convento, eastern Cuba) and Dominican Republic (Rio San Juan complex) and indicate that high-grade blocks of the La Corea mélange represent direct evidence of Aptian onset of subduction of very young Protocaribbean lithosphere.

Idael Blanco Quintero ⁽¹⁾, Joaquín A. Proenza ⁽²⁾, Antonio García Casco ^(1,3)

(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002-Granada, Spain. e-mail: blanco@ugr.es

(2) Departament de Cristal.lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, 08028-Barcelona, Spain

(3) Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Avda. Fuentenueva s/n, 18002 Granada, Spain

The La Corea mélange (Sierra Cristal, eastern Cuba) is a tectonic mélange containing medium- to high-pressure metamorphic blocks within a serpentinite matrix. The mélange is in tectonic contact with depleted ultramafic rocks of Mayarí-Cristal ophiolitic massif and overrides the volcanic arc Santo Domingo Formation. The age of overthrusting is latest Cretaceous – Danian, but the mélange started formation deep in the subduction channel (ca. 15 kbar) in the late early Cretaceous (ca. 120 Ma) associated with onset of SW-directed oceanic subduction in the region.

The La Corea serpentinites are frequently mylonitic, and commonly display a foliation defined by the preferential orientation of antigorite blades and spinels. The studied samples display non-pseudomorphic textures (interpenetrative and interlocking) and are formed by antigorite, with minor chrysotile, talc, carbonate, amphibole, chlorite, brucite, epidote, and relicts of primary Cr-spinel altered to ferrichromite and magnetite. The composition of relict cores of Cr-spinel has been considered here for petrogenetic considerations concerning the origin of the peridotitic protoliths.

Relictic Cr-rich spinel has Cr# [Cr/(Cr+Al)] ~ 0.85 and Mg# [Mg/(Mg+Fe²⁺)] ~ 0.32. The TiO₂ content is systematically low (<0.1 wt%). The Fe³⁺# [Fe³⁺/(Fe³⁺ + Cr + Al)] ranges between 0.01 and 0.02 corresponding to Fe₂O₃ contents between 0.35 and 1.75 wt%. MnO contents range from 0.33 to 0.6 wt%, ZnO between 0.17 to 0.5 wt%, and V₂O₅ (≤0.34 wt%) and NiO (<0.15 wt%) are very low. This composition resembles that of Cr-spinel from supra-subuction zone rocks, including that of Cr-spinel from dunites of the Mayarí-Cristal Massif (Cr# ³0.75), a portion of lithosphere located in the forearc region and that of Cr-spinel from the Téneme IAT volcanics (Cr# ³0.8), interpreted as a forearc component of the Upper Cretaceous volcanism in eastern Cuba. These relationships allow concluding that La Corea serpentinites formed by hydratation of a forearc mantle wedge (Caribbean lithosphere) by fluids derived from the SW-dipping subducted slab (Proto-Caribbean lithosphere). Hydration of forearc peridotites allowed the formation of the subduction channel at ca. 100-110 Ma and the subsequent exhumation of fragments of subducted oceanic crust (high- pressure blocks of the mélange) during the Cretaceous (100-70 Ma).

SIMILITUD Y DIFERENCIAS ENTRE LAS UNIDADES PINO SOLO, MESTANZA, CERRO DE CABRAS Y EL MANTO ALTURAS DE PIZARRAS DEL SUR. CLAVE PARA EL DESCIFRAMIENTO METAMÓRFICO

Dámaso Cáceres Govea ⁽¹⁾, Esther María Cruz Gámez ⁽¹⁾, Santa Gil González ⁽²⁾

(1) Departamento de Geología, Universidad de Pinar del Río. Calle Martí Final CP 20100. Email: dcaceres@geo.upr.edu.cu; (2) Centro de Investigaciones del Petróleo (CEINPET).

Las unidades Pino Solo, Mestanza y Cerro de Cabras, definidas como unidades metamorfizadas constituyen la denominada Faja Cangre. Por el Sur contacta tectónicamente con la falla Pinar y por el Norte lo hace mediante un plano de sobrecorrimientos con el Manto Alturas de Pizarras del Sur.

Las principales investigaciones relacionadas con el metamorfismo en la región se refieren a la Faja Cangre en su conjunto, sin prestar la debida atención a las particularidades de las diferentes unidades que la componen, por lo que numerosos investigadores han interpretado el metamorfismo en la región como un acontecimiento único, relacionado con los cabalgamientos, mientras otros relacionan la Faja Cangre con una zona de subducción. La presencia o no de las formaciones Ancón y Manacas en la Unidad Mestanza, ha servido de argumento para una u otra interpretación, situación ahora en parte despejada con la constatación de Ancón en el corte de dicha Unidad.

Para la realización del presente trabajo se realizaron cinco perfiles geológicos perpendiculares a las estructuras y extendidos desde la falla Pinar hasta el Cinturón de Mogotes, en el que se tomaron 125 secciones delgadas, muchas de ellas orientadas, se realizaron numerosas mediciones de elementos estructurales y se contó con análisis de Microsonda electrónica en anfíboles presentes en los metagabros.

A partir de la información obtenida durante el procesamiento de los datos colectados, se considera que en las unidades metamorfizadas que constituyen la Faja Cangre y el Manto Alturas de Pizarras del Sur, pueden distinguirse tres eventos metamórficos independientes y con características diferentes:

Cárdenas Párraga⁽¹⁾ J., García-Casco, A.^(1,2), Blanco Quintero, I.F.⁽¹⁾, Rojas Agramonte, Y.⁽³⁾, Kröner, A.⁽³⁾. Carrasquilla, S.⁽¹⁾, Lázaro, C.⁽¹⁾, Rodríguez Vega, A.⁽⁴⁾.

1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002-Granada, Spain

(2) Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Fuentenueva s/n, 18002-Granada, Spain

(4) Departamento de Geología, Instituto Superior Minero-Metalúrgico, Las Coloradas s/n, 83329-Moa, Cuba

Recently, a new occurrence of jadeitite jade has been discovered in the serpentinite-matrix subduction mélange of the Sierra del Convento (eastern Cuba) (García-Casco et al., 2009). Samples collected as loose blocks in the Macambo region of the mélange cluster into two groups according to geochemical and petrographic characteristics. The first one (group A) is predominantly composed of jadeite and omphacite, with minor to trace amounts of other constituents such as epidote, biotite, albite, sphene and apatite. The other one (group B) mainly consists of jadeite, omphacite, albite and epidote, with minor to trace amounts of paragonite, muscovite, sphene and apatite. The main textures recognized can be described as granoblastic (group A) and interlaced with foliation in several cases (group B). Both types of rock have grain size between 1-1.5 mm inside a recrystallized matrix (< 0.5mm size).

The contents of SiO₂ vary from 58 to 60 wt%, and from 52 to 53.5 wt% in groups A and B, respectively. Group A has lower Al₂O₃, CaO and K₂O contents and higher Na₂O and P₂O₅ contents. FeO_tot, TiO₂, MgO and MnO contents are similar in both groups. In group A, Rb and Ba contents fluctuate between 0.4–1.6 and 7.5–27.7 ppm respectively, being much lower than in group B (1.8–17.5 and 57–764 ppm). Both groups show analogous abundances in Cs, Nd and Hf (0.04–0.35, 0.3–1.9 and 0.1–0.33 ppm, respectively). Y and Yb contents are slightly higher in group B (<11 and 0.9 ppm, respectively). It is noteworthy the higher values of Zr in group A (90 – 180 ppm) compared to group B (<110 ppm).

Both groups display similar REE abundances to those of pegmatites of the Sierra del Convento mélange. These and other geochemical characteristics suggest a genetic link between pegmatitic H2O-rich melts and jade-forming fluids in the mélange. Our results indicate that two different types of pegmatite-derived fluids were involved in the formation of jadeitite jade rocks: a fluid rich in K, Ba, and Rb with a strong sedimentary component evolved from K-rich pegmatites (group B), and a depleted fluid with a strong mantelic component evolved from K-poor pegmatites (group A).

García-Casco, A., Rodríguez Vega, A., Cárdenas Párraga, J., Iturralde-Vinent, M. A., Lázaro, C., Blanco Quintero, I., Rojas- Agramonte, Y., Kröner, A., Núñez Cambra, K., Millán, G., Torres-Roldán, R. L., Carrasquilla, S. (2009). A new jadeitite jade locality (Sierra del Convento, Cuba): First report and some petrological and archaeological implications. Contributions to Mineralogy and Petrology (in press). DOI: 10.1007/s00410-008-0367-0

Cardona, A.⁽¹⁾, Montes, C.⁽¹⁾, Valencia, V. A.⁽²⁾, Farris, D.⁽¹⁾, Jaramillo, C.⁽¹⁾, Pepper, M. B. ⁽²⁾, Moron, S.⁽¹⁾, Silva, C. ⁽¹⁾

The growth of a continental magmatic arc is characterized by alternate steady-state phases replaced by episodic short-live voluminous inputs. These later “flare-ups” have been found to be connected to the formation of major intermediate batholith plutons in continental arcs, and they represent fundamental markers of the tectonic processes in convergence zones (Ducea, 2001).

Regional geochronological data from volcanic rock of the Panama intra-oceanic arc have shown that mafic volcanism was added to the upper crust in a continuous fashion between the Late Cretaceous and the Miocene (Bissinna, 2005). In contrast, ongoing petrological and U/Pb geochronological assessment to the exposed granitoids and detrital zircon sedimentary provenance analysis, suggest the existence of more punctuated periods for the formation of the intermediate-felsic middle crust. Granitoid consolidation phases occurred during the Late Cretaceous, Late Paleocene-Eocene and Early Oligocene. These stages correlate with some of the more strong tectonic modifications on the Central American margin of the Caribbean plate including the installation of the new subduction zone, major phases of thickened oceanic crust accretion and the break-up of the Farallon plate with associated changes in plate convergence vectors. It is therefore considered that the formation of intermediate crust in island arc setting may be triggered by “catastrophic” tectonic events, which may include crustal thickening and mature magmatic underplating similar to what is suggest by seismic analysis on active oceanic Pacific arcs (Kodaira et al., 2007).

Bisssina, 2005. A profile through the Central American landbridge in western Panama: 115 Ma Interplay between the Galápagos Hotspot and the Central American Subduction Zone“

Ducea, M., 2001. The California Arc: thick granitic batholiths, eclogitic residues, lithospheric-scale thrusting, and magmatic flareups. GSA Today 11, 4–10.

Kodaira, S.,Sato, T., Takahashi, N., Miura, S., Tamura, Y., Tatsumi, Y., Yoshiyuki, Y., 2007. New seismological constraints on growth of Continental crust in the Izu-Bonin intra-oceanic arc. Geology. 35, 1031-1034

Cardona, A.⁽¹⁾, García-Casco, A.^(2,3), Valencia, V.⁽⁴⁾, Weber, M.⁽⁵⁾ , Pepper, M⁽⁴⁾.

(2) Departamento de Mineralogía y Petrología, Universidad de Granada, Avda Fuentenueva sn, 18002,

(3) Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Avda. Fuentenueva s/n, 18002 Granada, Spain.

(5) Escuela de Geociencias y Medio Ambiente, Universidad Nacional de Colombia, Sede

Cretaceous metamorphic complexes of the Circum-Caribbean have shown to record the different convergence and tectonic scenarios that determine the evolution of the Caribbean plate and adjacent continental margins (Garcia-Casco et al., 2005, Pindell et al., 2005).

Petrological, geochemical and geochronological constraints from the northwesternmost segment of the Santa Marta region support the existence of at least two major metamorphic units with MORB to Back-Arc metavulcanic protoliths, juxtaposed along major structural discontinuities. U/Pb detrital zircon data show a transition from predominantly contemporaneous arc input in the outboard units to a South American type contribution in the inboard ones.

Thermobarometrical data show that the innermost belt records peak metamorphic conditions of 685° ± 70°C and 6.6 ± 0.8 Kb, and U/Pb zircon metamorphic rims suggest Late Maastrichian-Early Paleocene ages similar to spatilly related granitoids. This unit is juxtaposed against a greenschist to amphibolite facies unit, which attained its metamorphic peak of 529°± 52° and 5.5 ± 0.7 Kb between 80-65 Ma.

These metamorphic and and temporal constrains suggest that the metamorphic complexes in this segment of the South American margin record the collision of the Caribbean arc against the South American continent, and a higher grade metamorphism strongly associated to the magmatic evolution linked either to the post-collisional event or the early stages of the newly constructed continental arc.

García-Casco, A., Torres-Roldán, R., Iturralde-Vinent, M., Millán, G., Núñez, K., Lázaro, C and Rodríguez, A., 2006. High pressure metamorphism of ophiolites in Cuba. Geologica Acta. 4, 63-68.

Pindell, J., Kennan, L., Maresch, W. V., Stasnek, K. –P., Draper, G., Higgs, R., 2005. Plate Kinematic and crustal dynamics of circum-Caribbean arc-continent interactions: Tectonics controls on basin development in the Proto-Caribbean margins. In: Avé Lallemant, H. G., Sisson, V. B. (eds.): Caribbean-South American Plate Interactions, Venezuela. Geological Society of America special paper 394, 7-52.

Carrasquilla, S. ⁽¹⁾, García-Casco, A. ^(1,2), Pomo-González, J.C. ⁽³⁾, Rojas-Agramonte, Y.⁽⁴⁾, Kroner, A.⁽⁴⁾, Despaigne-Díaz, A.I.⁽³⁾, Blanco-Quintero, I.⁽¹⁾, Cárdenas-Párraga, J.⁽¹⁾

(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Avda. Fuentenueva s/n,18002 Granada, Spain. E-mail: scortiz@ugr.es

(2) Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Avda. Fuentenueva s/n, 18002 Granada, Spain. Email: agcasco@ugr.es

(3) Departamento de Geología, Universidad de Pinar del Río, Martí final 270, Pinar del Río, Cuba. Email: ibis@geo.upr.edu.cu

(4) Institut für Geowissenschaften, Universität Mainz, D-55099 Mainz, Germany.

The Mabujina complex (central Cuba), interpreted as late Jurassic to early Cretaceous arc root or basement (Somin & Millán, 1981), is tectonically located (top-to-bottom) between the primitive Lower Cretaceous Island Arc (Los Pasos unit) and the high-pressure Escambray massif. It is composed by two ”formations”, the Porvenir and Mabujina Formations (Dublan & Alvarez, 1986) and is intruded by the Manicaragua granodiorite. The Porvenir Formation is a sequence of arc rocks metamorphosed at the greenschists facies. The Mabujina Formation consists of basalts and basaltic andesites metamorphosed at the amphibolite facies. Abundant granitic-gneissic rocks are associated with the amphibolites showing both concordant and crosscutting relationships with respect to the main foliation of the amphibolites.

Whole rock major, trace element and isotopic data of the Mabujina amphibolites, granitic-gneissic rocks and Manicaragua granodiorite are treated in this work. Geochemistry of the Mabujina amphibolites indicates basalt to basaltic andesite composition and tholeiitic to calcalkaline affinity. REE patterns show enrichment in LREE that can be interpreted as IAT signature. The granitic-gneissic rocks from Mabujina complex can be divided into two series according to geochemical characteristics. The first one (group A) is a Na-Ca series, is dacitic in composition and of trondhjemitic affinity. The other one (group B) is a Na-K series, is rhyolitic in composition and of calcalkaline affinity. REE patterns of group A are similar to those of amphibolites, suggesting a co-magmatic relation of these rocks. Nevertheless, REE patterns of group B show enrichment in LREE and impoverishment in HREE. There are some samples which have intermediate composition between both groups. The Rb/Sr and Sm/Nd isotopic signatures indicate a mantelic source (e.g. Manicaragua granodiorite).

New unpublished zircon SHRIMP data of granitoid rocks from Mabujina complex indicate early late Cretaceous crystallization (ca. 93.5±1 - 90±1.2 Ma), suggesting early late Cretaceous to early Cretaceous age of metamorphism of the amphibolites. Zircon SHRIMP data of granodiorites from the Manicaragua batholith indicate late upper Cretaceous age for this post-metamorphic intrusion (ca. 87±0.6 - 84.2±0.8 Ma).

From these petrological and geochemical data it is concluded that Mabujina complex does not represent the oceanic basement of Cretaceous Volcanic Arc, but it constitutes a metamorphosed section of the volcanic arc (PIA?, arc root?). The age and origin of metamorphism remains uncertain. However, the suggested pre-90 Ma age of metamorphism is unrelated to the main episode of collision and high pressure metamorphism in the Escambray complex, invalidating the relationships such us that of a paired metamorphic belt.

Dublan, L., H. Álvarez-Sánchez et al, 1986. Informe final del levantamiento geológico y evaluación de los minerales útiles en escala 1:50000 del polígono CAME I, zona central del Escambray (inédito). Fondo geológico nacional, La Habana.

Somin, M. y G, Millán, 1981. Geología de los complejos metamórficos de Cuba (en ruso): Edit. Nauka, 219 p. Moscow.

In the Early Paleocene (Danian), a new east-west trending submarine volcanic arc was born in SE Cuba (Sierra Maestra-Cayman Ridge volcanic arc) on top of the Cretaceous volcanic terrane and its sedimentary cover. Several thousands meters of effusive and pyroclastic rocks, with marine sedimentary intercalations crop out in the Sierra Maestra mountains. Its corresponding back arc basin, lays to the north. Intruding the volcanic sequence in the Sierra Maestra are a large number of magmatic bodies. Pb/U analyses from zircons in the granitoids yielded ages from 60 Ma (Paleocene) to 48 Ma (Middle Eocene). Westward the volcanic arc and its back arc basin continues into the Cayman Ridge and Yucatán basin. A north dipping suduction zone should flank the Turquino-Cayman Ridge arc to the south and dense oceanic Caribbean crust dived below the arc. Coeval with the volcanic activity, a deformation event (Cuban orogeny) developed in western and central Cuba. Thrust sheets with ophiolites and Cretaceous volcanic rocks and small Lower Paleogene piggyback basins slide upon a northern foreland basin in western and central Cuba. Horizontal displacement attained more than 100 km.

Eocene volcanic arc rocks occur in the Northwestern Peninsula and the Montaignes Noires of Haiti and in Sierra de Neiba and Seibo of the Dominican Republic. If they originally were part of the Turquino-Cayman Ridge arc, then probably this structure was more than 1500 km long. The subducted (Caribbean) oceanic crust must have moved with a strong northward component along the 1000-1500 km long subduction zone of the Turquino-Cayman Ridge arc. In many of the Caribbean evolution models, at this time (Danian-Middle Eocene) the Caribbean plate is moving with a strong eastward component. In the present interpretation, the lithosphere to the north of the Turquino-Cayman Ridge subduction zone was already accreted to the NA plate in the Paleocene, and the southeastern boundary of the NA plate was a north dipping subduction zone. The fold and thrust belt along northern Cuba is not a consequence of the Caribbean and Northamerican plates collision, because the Caribbean plate could not reach the NorthAmerican margin and was consumed along the Turquino-Cayman Ridge subduction zone. Beginning in the Middle Eocene, after subduction ended, a new plate boundary developed along the Oriente transform fault.

José L. Cuevas Ojeda, Rosa Álvarez Hernández, Eduardo Pérez Almaguer y Bárbara Polo González

Departamento de Geología Ambiental, Geofísica y Riesgos, Instituto de Geofísica y Astronomía, CUBA

El presente trabajo es la primera parte de una investigación que en general estuvo dirigida a caracterizar el comportamiento de la corteza terrestre en el Caribe occidental, estimando la superficie límite corteza-manto para establecer las características más peculiares de la distribución de las profundidades de este límite en el área de estudio. Esta primera dirección de trabajo estuvo enfocada a la realización de un estudio de los campos potenciales en Cuba, que actualizara la información existente, para posteriormente poder incluir la correspondiente a Cuba, en la información geofísica del Caribe occidental. Esta información geofísica la constituyeron los mapas de anomalías de Bouguer total, primero de su tipo en Cuba y uno que tuviera en cuenta el campo gravimetrito sobre la base de la isostasia en Cuba, este último también primero para la región estudiada, los que sirvieron posteriormente como control en la predicción del límite corteza-manto y para los estudios de isostasia y sismicidad, que incluye: una generalización de las características de las principales anomalías y su posible naturaleza, un análisis de las principales consideraciones sobre la determinación de zonas potencialmente sísmicas y por ultimo un análisis de la función isostática del espesor de la corteza en esta región. En el actual trabajo se incluye como novedad el mapa de anomalías isostáticas residuales de toda Cuba, completándose así la información de la parte más occidental del país, que no había sido incluida con anterioridad. Se caracteriza de manera generalizada el comportamiento del campo magnético en Cuba.

El área La Sierrita se localiza en la parte suroeste de la cúpula de Trinidad en el macizo Escambray, Cuba Central. Se caracteriza por rocas metamorfizadas en la facie de esquistos verdes (unidad tectónica I) y en metamorfismo de alta presión reportado en rocas eclogíticas (unidad tectónica III) según la clasificación de Millán (1997). El objetivo del trabajo se basó en el estudio detallado de la estructura geológica de la zona con las fases de deformación involucradas para descifrar la evolución geológica de la cúpula y el macizo, basado en un área de detalle. Se realizaron 8 perfiles geológicos a través de los cuales se midieron e interpretaron los principales parámetros estructurales (foliaciones, estructuras plicativas y disyuntivas: ejes de pliegues, lineaciones minerales y de intersección, fallas, y distintos tipos de grietas). La zona se ha subdividido en 5 napes para su caracterización estructural, según tipos litológicos, estructuras y contactos. Las rocas características del metamorfismo de alta presión forman el nape Monforte y las rocas de metamorfismo en facie de esquistos verdes (GSFU) en tres nombrados: La Sierrita, Yaguanabo y Rio Chiquito. Se mapearon tres superficies planares asociadas al metamorfismo S₁, S₂ y S_3.

Se han detectado cinco fases de deformación en la zona formadas a diferentes niveles estructurales. La fase D1 genera la esquistosidad S1 con plegamiento F1 asociado. Sus pliegues son de tipo isoclinal hasta similares de orden centímetrico y métrico. Se forma en un ambiente dúctil. La Fase D2 forma la esquistosidad S2 con pliegues F2 asimétricos, sinusoidales, disarmónicos e isoclinales de pocos metros. Los ejes de los pliegues se hunden al este-oeste. Se forma una lineación L2 y L02. Se produce en un ambiente dúctil. La fase D3 forma pliegues F3 asimétricos vergentes al noreste cuyos ejes se hunden hacia el noroeste-sureste ligados a un proceso de sobrecorrimiento de las unidades hacia el noreste. Esta situación se refleja en todos los napes. Se forman lineaciones minerales de actinolita y micas y lineaciones de intersección L3 cuya orientación es similar y coincide con los ejes de los pliegues F3. El contacto entre napes está marcado por clivaje sigmoidal milonítico, estructuras sigma rotadas, pliegues de arrastre y estructuras duplex que indican sentido de transporte tectónico al noreste. Se forma un pliegue regional F3 volcado al noreste que involucra a todas las unidades de las GSFU en cuya cima cabalga el nape Monforte. Las grietas de cizalla conjugada indican orientación del máximo estrés compresivo σ1 al norte-noreste variando desde 003° hasta 98°, coincidiendo con los movimientos reportados por otros indicadores. Se produce en un ambiente dúctil-frágil. La fase D4 se caracteriza por la formación de un clivaje de fractura S4 asociada a pliegues abiertos de plano axial vertical y que coincide con la formación de la cúpula. Los pliegues F4 son de orden de métrico y hectométrico y sus ejes se hunden al suroeste-noreste. Se forma en un ambiente dúctil-frágil. La fase de deformación D5 es tardía y está relacionada con la formación de fallas transcurrentes de dirección sureste-noroeste que constiyuen fracturas de riedel secundarias probablemente asociadas a la formación de la falla La Trocha. En el estadío final se produce el relajamiento de la estructura con la formación de fallas normales de bajo ángulo más abundantes hacia el borde de la cúpula.

La fase D1 y D2 por su distribución y los elementos que involucra estarían relacionadas a un proceso de subducción (D1) y subducción-colisión (D2) que involucró a todas las secuencias y causó el metamorfismo de alta presión del nape Monforte. Los napes de las GSFU penetraron a menores profundidades y se metamorfizaron en la facie de los esquistos verdes. Durante la fase D3 se produjo la estructura nape escamada del área durante cabalgamientos en dirección noreste. La superficies planares S1-3 reflejan orientación de minerales evidenciando el sincronismo del metamorfismo con las deformaciones. Las fases D4 y D5 son tardías y postmetamórficas y se formaron después de conformada la estructura de napes del área.

MSc. Ana Ibis Despaigne Díaz (1) Antonio García Casco (2) Dámaso Cáceres Govea (1) Jose Carlos Pomo Gónzalez (1) Sandra Carrasquilla Ortiz (2)

Las rocas de la facie esquistos verdes del macizo Escambray se encuentran localizadas hacia el centro de la cúpula Trinidad en el macizo Escambray, Cuba central. La estructura interna está caracterizada por tres deformaciones dúctiles sinmetamórficas D₁, D₂ y D₃ con orientación de minerales y una deformación D₄ post metamórfica generada en niveles estructurales superiores y asociada a la formación de la cúpula. Las rocas estudiadas para el análisis comprenden metabasitas, calcoesquistos de variada composición mineralógica con calcita como mineral representativo y mica blanca, cuarzo, anfibol, clorita, esfena y epidota, esquistos cuarzo micáceos con granate y mármoles. La correlación entre la megaestructura y la microestructura revelaron la existencia de asociaciones minerales relacionadas a cada fase de deformación lo que permite postular que la fase D₁ es relíctica tanto en niveles macro como microestructurales. Los minerales de esta fase están preservados dentro de porfiroblastos de albita formando inclusiones orientadas discordantes con la foliación principal S₂. En otros casos está representada por cristales de mica blanca (phengitas) dentro de albita de tamaño mayor que los de la matriz S₂. En equilibrio con estas phengitas se encuentran los núcleos viejos de albita, epidotas y cloritas de la matriz. La fase D₂ es la mejor conservada, penetrativa y consistente de todas. En todos los tipos de rocas aparece como una prominente esquistosidad S₂ con orientación de albita, anfíbol (actinolita y magnesio hornblenda), biotita, feldespato potásico, clorita, epidota, granate y esfena. La crenulación de esta S₂ forma un nuevo clivaje planar axial S₃ asociado a una fase D₃ y que genera la reorientación de minerales formados en la fase D₂. En esta dirección se orientan albitas, epidotas, esfenas, cloritas y phengitas. La correlación de la química mineral de las asociaciones minerales de cada fase con las foliaciones permite establecer un rango de presiones y temperaturas en las que estas ocurrieron. El contenido de Si en las phengitas es un indicador de condiciones de presión. Las phengitas incluidas en albita (pre D₂) contienen Si =6,29-6,80 apfu, en la dirección S₂ (Si=6,45-7,25 apfu) y en S₃ (Si=6,45-6,85 apfu) indicando que estas rocas han sufrido condiciones de altas presiones con aumento desde D₁ a D₂ y caída en D₃. Las mayores temperaturas se alcanzan durante D₂ y se evidencia por la presencia y orientación de magnesio hornblenda y biotita en al matriz S₂. De acuerdo a esto la fase D₁ es prógrada, la fase D₂ constituye el pico metamórfico (termobárico) y la fase D₃ a una descompresión. La existencia de micas de alta presión en estas rocas evidencia el metamorfismo de las mismas asociado a una zona de subducción en la cual la fase D₁ y D₂ están relacionadas al proceso de subducción mientras que la fase D₃ está ligada al proceso de acreción-exhumación. Las presiones experimentadas superan los 8 kbars y temperaturas ³ 400°C. Durante esta última fase se gestó la estructura de napes del área con el apilamiento de mantos en dirección NE. En el contexto geodinámico del Caribe, la estructura del área refleja la inserción del Escambray en una zona de subducción durante el Cretácico tardío y constituye una evidencia del proceso de colisión-acreción de la placa Caribe y los macizos sedimentarios Mesozoicos situados en el dominio paleogeográfico del proto Caribe.

Duque-Trujillo, J.F.,⁽¹⁾, Orozco-Esquivel, T.,⁽¹⁾, Cardona, A.,(2), Ferrari, L. ⁽¹⁾, Solari, L., ⁽¹⁾.

Late Cretaceous to Paleogene tectonic within the Circum-caribbean area is dominated by the accretion of Caribbean- related intra-oceanic elements to the margins of the Americas, which were previously mainly ruled by passive margin tectonics.

An evidence of this tectonic change is the Santa Marta batholith ant its related rocks. An extensive and very complete series of intrusive rocks, traditionally considered of Paleogene age (Tshanz et al., 1974, GSA Bull, 85, 273-284), but whose link whit the Caribbean tectonics have not been yet considered.

This plutonic complex includes the Santa Marta batholith and the Latal, Toribio and Buritaca plutons. They intrude both a Cretaceous allocthonous Caribbean-related metamorphic terrane as well as the Precambrian and Late Paleozoic basement of the South American margin. New field data allowed us to identify a complex magmatic activity, represented by the diversity of rocks found, including five (5) different magmatic facies inside of the Santa Marta batholith, mafic enclaves, mafic cumulates and two mica-garnet bearing granites. This diversity indicates a complex magmatic history whit assimilation, mixing and recirculation of materials from the deepest parts of the magmatic chamber.

Geochemical mayor elements analysis show a complete subalkaline mainly metaluminouse, I-type magmatic suite whit some peraluminous, S-Tipe rocks. They are mainly composed by medium K contents, how ever some rocks show low and high K contents in all of SiO₂ range. The whole suite from cumulates to granites have the same trace element trends where the magmatic arc signature is clear, and dominated by the enrichment between LILE vs HFSE and also among LREE vs HREE. The Ba, U, Pb, Sr, Nb, Ta and Eu behavior indicates a very important action of aqueous fluids in the genesis of all this magmatism and a fractionated crystallization. Some chemical differences are seen primarily between the main tonalitic rock whit the cumulitic rocks and enclaves, who are representing a deeper and less evolved magmas. The S-Type granites are representing more evolved magmas, maybe the firsts melt from the series who have assimilated some sediments in the ascent.

The age of the main magmatic pulse is ranging from 55 to 54 My, represented by the main part of the Santa Marta batholith and Latal pluton. How ever, ages around 58 to 57 My have been obtained for the eastern part of the Santa Marta batholith, for some mafic enclaves and Toribio pluton. These last two could possibly be genetically related. Nevertheless the magmatism seems to begin at 64 to 62 My, whit the S-Type granites and finish at 51 to 50 My whit the intrusion of Buritaca pluton, some facies of the Santa Marta batholith and aplitic dikes.

In general terms, the generation mechanism for this magmatism can be related to the interaction between South American and Caribbean plates in the onset of a new subduction zone context during Paleocene-Eocene. This subduction zone and its related magmatic arc have been scattered due to the relative dextral movement of the Caribean Plate respect to South American plate.

Others plutons whit characteristics are reported from Cuba, Hispaniola, Puerto Rico, Virgin Islands and Lesser Antilles (Rojas-Agramonte et al, 2004, Chem. Geol., 213, 307– 324), and others like Parashi pluton in Colombia (Cardona, A. et al, 2007, XI Colombian Geology Congress); All of these forming a circun-Caribbean magmatic arc related to subduction and syn-post deformation processes around the plate.

Tshanz et al.,1974. Geologic evolution of the Sierra Nevada de Santa Marta, Northeastern Colombia. GSA Bull, 85, 273-284.

Rojas-Agramonte Neubauer, F., Kröner, A., Wan, Y. S., Liu, D. Y., García-Delgado, D. E., Handler, R., 2004. Geochemistry and age of late orogenic island arc granitoids in the Sierra Maestra, Cuba: evidence for subduction magmatism in the early Palaeogene.Chem. Geol., 213, 307– 324.

PLUME MAGMATISM INDUCED BY SLAB ROLLBACK: TRACE ELEMENT AND ISOTOPIC INSIGHTS FROM THE LATEST CRETACEOUS CARIBBEAN ISLAND-ARC IN HISPANIOLA.

Escuder Viruete, J. ⁽¹⁾; Pérez-Estaún, A. ⁽²⁾; Joubert, M.⁽³⁾; Weis, D.⁽⁴⁾.

(1) Instituto Geológico y Minero de España, C. Ríos Rosas 23, 28003 Madrid. Spain. j.escuder@igme.es

(2) Instituto Ciencias Tierra Jaume Almera-CSIC. Lluís Solé Sabarís s/n. 08028 Barcelona, Spain. andres@ija.csic.es

(4) Pacific Centre for Isotopic and Geochemical Research. University of British Columbia, 6339 Stores Road Vancouver, BC V6T-1Z4. Canada. dweis@eos.ubc.ca

Located in the Cordillera Central of Hispaniola, the Pelona-Pico Duarte basalts Fm (PPDB) offers an opportunity to study an on-land section of the Late Cretaceous Caribbean-Colombian oceanic plateau (CCOP). Geochemical, Sr-Nd isotope, and ⁴⁰Ar-³⁹Ar radiometric age data combined with detailed mapping have shown that the PPDB is composed of a massive and homogeneous >2.5 km thick pile of basaltic submarine flows, mostly aphyric and amygdalar, frequently banded and rarely porphyritic. Lava flows are locally interlayered by mafic tuffs and intruded by synvolcanic dykes and sills of basalts and dolerite. A whole rock ⁴⁰Ar-³⁹Ar plateau age of 68.40±0.75 Ma indicates volcanism took place around the Campanian-Maastrichtian boundary.

For a restricted range of 46.2-50.2 wt.% SiO₂, the PPDB have relatively low CaO (10.0-13.1 wt.%) and Al₂O₃ (12.8-14.3 wt.%) contents, and high contents in alkalis (2.0-2.6 wt.%), TiO₂ (1.5-3.6 wt.%), and Fe₂O_3T (10.7-13.1 wt.%). The Mg# values of 58-52 indicate that these lavas have undergone low to moderate amounts of fractionation. These basalts are transitional and alkalic and show a typical tholeiitic trend of increasing TiO₂, Fe₂O_3T, CaO, Al₂O₃, Zr and Nb, for decreasing MgO (Cr or Ni). These trends can be attributed to the fractionation of olivine plus Cr-spinel, clinopyroxene (Ti-augite) and plagioclase, observed as microphenocrysts in the lavas. The basalts have LREE enriched ([La/Nd]_N=1.5-2.2) and depleted HREE ([Sm/Yb]_N=2.0-3.7) patterns, with very high Nb contents (9-30 ppm). These patterns and other trace element ratios are characteristic of modern day alkalic oceanic-island basalts. In terms of Sr-Nd isotopic composition, the PPDB samples are homogeneous and enriched relative to older CCOP units in Hispaniola, with (⁸⁷Sr/⁸⁶Sr)_i ratios between 0.70330 and 0.70348 at very restricted range of (e_Nd)_i values between +5.0 and +5.9 (where i=68 Ma). The PPDB are interpreted as partial melts of a plume-related, deep enriched source, which have not been contaminated by active subduction.

The elevated TiO₂ and Zr₁₅ contents, high [La/Nd]_N and [Sm/Yb]_N ratios, combined with (e_Nd)_i<+5.9 values in the analized samples are consistent with a primitive mantle source consisting of spinel lherzolite with 25-35% amounts of garnet lherzolite. Mantle melt modelling indicates that this source underwent about 6-15% melting to form PPDB magmas. Alternatively, these magmas can also be explained by mixing processes in the melt column, and result by mixing of very small degree melts (<2%) of a deeper garnet lherzolite region and 15-25% melting of a shallower source region.

The PPDB have significantly different values of petrogenetic tracers than underlying pre-Campanian arc-related lavas, indicating that they were derived from different mantle sources. These basalts have geochemical affinities with the mantle domain influenced by the Late Cretaceous Caribbean plume, suggesting that enriched mantle was flowing toward the NE, to the mantle wedge region of the Caribbean island-arc, in response to rollback of the SW-directed subduction of the proto-Caribbean slab.

U-Pb CONSTRAINTS ON THE TIMING OF IGNEOUS AND METAMORPHIC EVENTS IN THE RIO SAN JUAN COMPLEX, NORTHERN HISPANIOLA.

Escuder Viruete, J. ⁽¹⁾; Friedman, R. ⁽²⁾; Pérez-Estaún, A. ⁽³⁾.

(1) Instituto Geológico y Minero de España, C. Ríos Rosas 23, 28003 Madrid. Spain. j.escuder@igme.es

(2) Pacific Centre for Isotopic and Geochemical Research. University of British Columbia, 6339 Stores Road Vancouver, BC V6T-1Z4. Canada. rfriedma@eos.ubc.ca

(3) Instituto Ciencias Tierra Jaume Almera-CSIC. Lluís Solé Sabarís s/n. 08028 Barcelona, Spain. andres@ija.csic.es

We report here new regional cartographic and U-Pb data of the Río San Juan Complex, northern Hispaniola, in order to constraint the timing of some igneous and metamorphic events. The ultramafic belt that outcrops the northern area of the Río San Juan Complex is a largely deformed from ductile to brittle conditions, serpentinite-matrix mélange, called the Jagua Clara mélange. It is bordered on the south across the El Higuero fault by the Puerca Gorda and the El Guineal metavolcanic rocks of the El Morrito unit. The serpentinite protolith was peridotite tectonite (harzburgite>dunite), comprising upper mantle, and now preserved as tectonic blocks of massive serpentinized Gaspar Hernández peridotite. The native blocks of peridotite range from <1 m up to 3.5 km of structural thickness, and are enclosed in a matrix of foliated and intensely sheared serpentinite. Non-native mélange blocks in the serpentinite are high-P blocks, metabasalts (El Guineal mafic schists and greenstones), sparse mafic plutonic rocks (gabbros), white marbles and rare ribbon chert. The ophiolitic serpentinite mélange protolith was therefore basaltic oceanic crust above uppermost mantle, overlain by deep-sea sediments. An open-ocean setting, far from a continent margin or volcanic arc, is inferred from the geochemical affinity of metabasalts and the absence of terrigenous clastic or volcaniclastic sediments. Five zircon fractions recovered from a gabbro sill intrusive in the Gaspar Hernandez serpentinized peridotite yielded concordant, overlapping and precise results, which give a Concordia age of 136.4±0.32 Ma, which is interpreted as the crystallization age of the a basaltic magma produced by mantle fusion processes. This Valangian-Hauterivian boundary age is the oldest age obtained until now in the Dominican Republic. Possibly, it is one of few outcropping ophiolitic remains of proto-Caribbean oceanic lithosphere, formed when North and South America separated in the Lower Cretaceous, which escaped subduction (no high-P metamorphism) and was incorporated in the mélange.

The Jagua Clara mélange was intruded by concordant sheet-like bodies of strongly foliated muscovite-bearing leucogranites. Typically, these felsic intrusives are deformed from magmatic to solid-state conditions in the core and solid-state conditions in the rim. The internal magmatic foliation and the mylonitic fabric in the deformed external sector of the leucogranites parallels the intrusive contact and the regional foliation of the enclosing serpentinites. Zircons extracted from this sample gives a Concordia lower intercept of 68.9±0.3 Ma, which match to other geochronological data recently published for cooling at T<400º C in the high-P blocks. This Campanian-Maastrichtian boundary U-Pb age is interpreted as the crystallization age of the syn-kinematic leucogranite and, as field evidence indicates, ductile shearing deformation in the mélange was at least from 69 Ma. In this sample, a Concordia superior interception at 1042.8±2.8 Ma (4 points regression) suggest Greenville core zircon ages mixed with rims of Cretaceous ages. These leucogranites are probably melts of subducted siliciclastic sediments derived from the southern continental margin of North America plate (i.e. Mesozoic sediments deposited onto the Bahamas platform that eroded a Greenville basement). Taken together, these ages implies: (1) in the latest Cretaceous the polarity of subduction was from the NE; (2) the subduction channel represented by the serpentinite mélange was close to the margin of North America and received its terrigenous influence; and (3) the greenville inheritances do not find southward in Hispaniola.

MESOZOIC TO EOCENE PLATE TECTONIC OF THE CIRCUM PACIFIC AREA: NEW CONSTRAINTS ON FAR TRAVEL EXOTIC TERRANES, SUBDUCTION ZONE MELANGES AND ARC-ARC COLLISIONS.

Flores, K., Stampfli, G., Baumgartner, P.O, Gracia-Garay, C., & Hochard, C.⁽¹⁾

(1) Institut de géologie et paléontologie, Université de Lausanne, Anthropole, CH-1015 Lausanne, Switzerland. E-mail: Kennet.FloresReyes@unil.ch

A new tectonic synthesis of the plate tectonic evolution of the Circum Pacific area since the Pangea breakup (230 Ma, Late Triassic) has been elaborated based on data derived from different geological and geodynamic constraints. Besides our own geological researches in Central America, the distribution, composition and age of the Circum Pacific HP/LT serpentinite mélanges and belts, magmatic activity, sedimentary patterns, metamorphism, structural geology, paleomagnetic data and geophysics have been systematically compiled.

Reconstructions were performed using ArcGis 9.2, which enabled us to apply and quantify rotational motions and spreading/subduction rates to the numerous plates and tectonic blocks involved in the evolution of the Circum Pacific area. Boundary conditions are provided by the relative motions of the different plates with respect to fix Europe. Plate tectonic concepts are applied all along the process and plate boundaries are built and transformed in space and time. Plate velocities can be calculated at any time and are never in excess of 20cm/y.

At 230-220Ma the Pangea break-up is the main event affecting the central American zone, with the onset of rifts that separated North and South America. Two rift zones are envisaged, one in the Gulf of Mexico, the other in the proto Caribbean area that evolved to oceanic areas in the Jurassic. In the Pacific, terranes derived from surrounding continental areas are being distributed in different direction. The Stikinia-Wrangellia terrane most likely derived from Australia is now colliding with island arcs derived from North America. The resulting collision triggered rifting within this intra-oceanic collision zone, and finally spreading took place between Stikinia and Wrangellia, the latter being stranded in the oceanic area, whereas the former continued northeastward toward North America.

At 200Ma Wrangellia is caught up by an arc derived from the southern Pacific area (e.g. Kodiak), from this collision the present day Pacific plate appeared in the early Jurassic. This was accompanied by the inception of the intra-oceanic arcs of Guerrero, Phoenix, Inzanagi and Wrangellia around a proto-Pacific triangular area. Since 180Ma a diachronous collision of the Stikinia arc with a NAM derived terrane (e.g. Cassiar) took place and continued southward with the collision of the Guerrero Phoenix arc with the North and South American continental active margins and their back-arcs.

A new generation of intra-oceanic arc and the Caribbean plateau substratum appeared in the Early Cretaceous. These collided in turn with the Caribbean arc derived from the former collision of the Guerrero terrane with the Chortis plate. Ensuing subduction reversal brought the imbricate arcs and plateau into the proto-Caribbean space in the Paleogene. In that space, the Cuban intra-oceanic arc collided with the Maya block promontory and Bahamian plateau from the late Cretaceous to the Paleocene.

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PROPOSAL FOR THE DECLARATION OF GEOLOGICAL HERITAGE FOR A BLOCK OF ECLOGITE, SANTA CLARA PROVINCE, CUBA

(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002-Granada, Spain

(2) Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Fuentenueva s/n, 18002-Granada, Spain

(3) Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100, Cuba.

Society has the right to know and appreciate the beauty of Nature, and scientists have the responsibility to transfer knowledge and scientific sensibility to Society. Since the early ages of Human Being questions concerning our environment and its evolution (change) have plagued and agitated sensible characters. After the notable progress of Science since the XVIII a.D., Earth scientists have made evident the lengthy history of our Planet, the diversity of environments, geographies, and creatures that have paved the way into present day Earth. Such diversified scenarios are the result of a number of important terrestrial and extraterrestrial factors that control the evolution of our Planet, including Plate Tectonics which is a major driving force for change of the Earth System. Among the various forms of expression of Plate Tectonics, subduction of oceanic lithosphere stands out. By means of subduction, huge amount of lithospheric rock material is deeply buried and recycled along thousands of km in length into the deep mantle, involving huge amount of energy. This process causes significant change in geographies, environments, and ecosystems at the scale of millions of years. Approximately 98% of the subducted rock material is dispersed and recycled in the deep mantle and never returns to the Earth’s surface. However, under certain circumstances, subducted rock fragments return, giving scientist the possibility to decipher processes that contributed to the transformation of our Planet. In addition, these rocks tell us about processes that greatly affect our daily lives, such as the volcanic eruptions, earthquakes, and the deathly 2005 tsunami of Sumatra. Cuba is plenty of rocks that experienced subduction and have returned to Earth’s surface. They are found all along the >1100 km of the main island, from the Cabo San Antonio to Punta Maisí. These rocks tell us about a long history of change in the Caribbean region since the Aptian (ca. 120 million years ago), when the Tyrannosaurus rex was only an idea in the plan for the Evolution of the Species. Most of these rocks are found as exotic blocks in tectonic serpentinite mélanges that make much of the geological backbone of Cuba. A beautiful example of this rock type, an eclogite block, is found in the Santa Clara-Encrucijada road (N 22º 32′ 20.3″ - W 079º 54′ 19.3″), in the tectonic mélange of central Cuba. The block has ca. 5 m² in area ca. 1.5 m in height, and is located is just a few meters from the road being easily accessible to the public. The rock is beautiful, with a distinctive banded structure and made of amazing crystals of garnet and omphacite that are retrogressed by calcic amphibole and epidote. The rock originally formed close to the Earth’s surface as basalt in the lost Protocaribbean ocean, and was buried down into the mantle to ca. 70 km depth by ca. 120 My ago, during the process of disappearance of such ocean. It is certainly one of the oldest rocks in Cuba. In addition, their minerals show a delicate chemical structure of oscillatory zoning denoting complex thermodynamic (i.e, tectonic) processes during subduction. Such type of zoning is certainly a rare feature of eclogite, making this rock of particular scientific interest for the worldwide geological community. For all these reasons, we strongly recommend the Cuban Government to declare this block of eclogite as a Geological Heritage of the Cuban People, as an effort to acknowledge the International Year of Planet Earth (2007-2009) proclaimed by the United Nations General Assembly in 2006.

García-Casco, A.^(1,2), Rodríguez Vega, A.⁽³⁾, Rojas Agramonte, Y.⁽⁴⁾, Kröner, A.⁽⁴⁾, Cárdenas Párraga⁽¹⁾, J., Iturralde-Vinent, M. A.⁽⁵⁾, Lázaro, C.⁽¹⁾, Blanco Quintero, I.F.⁽¹⁾, Núñez Cambra, K.⁽⁶⁾, Millán, G.⁽⁶⁾, Torres-Roldán, R.L.⁽¹⁾, Carrasquilla, S.⁽¹⁾

(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002-Granada, Spain

(2) Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Fuentenueva s/n, 18002-Granada, Spain

(3) Departamento de Geología, Instituto Superior Minero-Metalúrgico, Las Coloradas s/n, 83329-Moa, Cuba

(5) Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100, Cuba.

(6) Instituto de Geología y Paleontología, Via Blanca y Carretera Central, La Habana, Cuba.

A new jadeitite jade locality has been discovered in the serpentinite-matrix subduction mélange of the Sierra del Convento (eastern Cuba), associated with tectonic blocks of garnet-epidote amphibolite, tonalitic-trondhjemitic epidote gneiss, and blueschist. The mineral assemblages of jadeitite jade and jadeite rocks are varied and include combinations of jadeite, omphacite, albite, paragonite, analcime, clinozoisite-epidote, apatite, phlogopite, phengite, chlorite, glaucophane, titanite, rutile, zircon, and quartz, formed during various stages in the P-T evolution of these rocks. Field relationships are obscure, but some samples composed almost exclusively of jadeite show evidence of crystallization from fluids in veins. In one of these samples studied in detail jadeite shows complex textural and chemical characteristics (including oscillatory zoning, Fig. 1) that denote growth in a changing chemical medium. It is proposed that interaction of an Al-Na-rich fluid with ultramafic rocks produced Al-Na-Mg-Ca fluids of varying composition. Episodic infiltration of these fluids, as a result of episodic opening of the veins, developed oscillatory zoning by direct precipitation from fluid and after reaction of fluid with pre-existing jadeite at >550 ºC. The latest infiltrating fluids were richer in Mg-Ca, favouring the formation of omphacite and Mg-Ca rich jadeite in open voids and the replacement of earlier jadeite by fine-grained omphacite+jadeite at 550-560 ºC. Taking all the lines of evidence together, we consider that jadeite-forming fluids in the Sierra del Convento mélange originally evolved from hydrous tonalitic-trondhjemitic partial melts in a subduction environment at high temperature. The inferred >550 ºC conditions of formation of the studied jadeitite sample is higher than normally recorded at other jadeitite localities and strengthens this view. P-T path estimates in the Sierra del Convento mélange indicate that this temperature condition would have been reached at ca. 15 kbar. That the original fluids evolved from tonalitic-trondhjemitic rocks of the mélange is indicated by early Cretaceous SHRIMP zircon ²⁰⁶Pb/²³⁸U ages of 105-110 Ma from jadeitite, corresponding to the isobaric cooling stage of the trondhjemitic liquids of the Sierra del Convento at ca. 15 kbar. This new occurrence of jadeite in Cuba opens important perspectives for archaeological studies of pre-Columbian jade artifacts in the Caribbean region.

Harlow, G.E. ⁽¹⁾, Sisson, V.B. ⁽²⁾, Sorensen, S.S. ⁽³⁾, Brueckner, H.K ⁽⁴⁾ and Simons, K.K. ⁽⁵⁾

(1) Department of Earth & Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA. E-mail: gharlow@amnh.org

(2) Geosciences Department, University of Houston, Houston, TX, 77204 USA. E-mail: j_sisson@netzero.com

(3) Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560 USA. E-mail: sorensen@si.edu

(4) School of Earth & Environ. Sciences, Queens College, CUNY, Flushing, NY 11367 USA. E-mail: hannes@ldeo.columbia.edu

(5) Rosenstiel School, Univ. Miami, Miami, FL 33149-1098 USA. E-mail: ksimons@rsmas.miami.edu

Jadeitite, a rock composed principally of jadeitic pyroxene, is the original “piedra de yjada” or jade of the New World. Exploited initially by Mesoamerican peoples and dispersed around the Caribbean basin, it is now recognized as a HP-LT rock crystallized from hydrous subduction-related fluids in serpentinizing peridotite and emplaced in certain serpentinite mélanges worldwide, but particularly along the northern Caribbean boundary in Guatemala, Cuba, and the Dominican Republic. Our research in Guatemala documents jadeitites from serpentinite over a 200 km E-W extent just north of the Motagua fault (MF) and three distinct sources in a region 11 km across south of the fault.

Jadeitite from south of the MF is distinct both from that north of fault and among the occurrences in fault slices of serpentinite. Jadeitite occurs with lawsonite eclogite (T = 350-450°C, P = 20-26 kbar) and contains primary phengite, quartz and lawsonite, interpreted as T = 300-400°C, P = 12-20 kbar. Jadeitite occurring with omphacite-glaucophane blueschists also contains Qtz but no Lws and sometimes Ab yields T = 300-400°C P = 12-20 kbar. Pumpellyite jadeitite occurs with lawsonite-glaucophane blueschists and contains Ab and no Qtz, yielding T <200-~300°C, P = 6-9 kbar.

Jadeitite north of the MF is remarkably uniform in phase assemblage except for a western-most lavender jadeitite. Occurring with clinozoisite eclogite (to West) and garnet-clinozoisite amphibolite (to East), jadeitite commonly contains white-tan mica, Omp, Ab, zoisite, Anl and NO quartz, whereas lavender jadeitite contains late-stage Ab +Lws + Grs + Pmp. Omphacite-taramite metabasite, albitite, and Ab-phengite rock occurs ubiquitously with northern jadeitite, but not with southern. All this suggests P = 6-10 kb and T = 300-400°C, but a lower P-T for lavender jadeitite.

Sm-Nd dating of eclogite north of MF yields an age of ~130 Ma whereas Ar-Ar dating of mica and amphibole from HP-LT rocks yields ages from 51 to 88 Ma. Sm-Nd dating of southern eclogite also yields ~130 Ma age as does Ar-Ar dating of mica from HP-LT rocks. Age discrepancies across the Motagua fault are best explained by a ~70 Ma collision of the northern terrain with the Maya block, which obducted the Sierra de Santa Cruz and reset Ar-Ar clocks (i.e., T≥400°C) prior to left-lateral translation of the Chortís block (south of MF). Jadeitite occurrence in collisions with a strong lateral component is common.

Trace-element and Li-isotope geochemistry of jadeitites suggests a variable mixture of fluid-derived components from altered oceanic crust and continental sediment, the latter important (> 10%) in Guatemala jadeitite.

Study of jades from the islands of Antigua, Vieques (P.R.), and St. Croix (U.S.V.I.) yield phase assemblages most consistent with Guatemalan jadeitite from south of the MF and not other Caribbean sources.

W.T. Jolly⁽¹⁾, J.F. Lewis⁽²⁾, J.A. Proenza⁽³⁾ and E.G. Lidiak ⁽⁴⁾

1) Dept. of Earth Sciences, Brock University, St. Catherines, Onatrio, Canada, L2S3A1

2) Dept. of Earth and Environmental Sciences, George Washington University, Washington, D.C. 20052.

3) Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí I Franquès, s/n, 08028 Barcelona, Spain.

4) Dept. of Geology and Planetary Science, University of Pittsburg, Pennsylvania 15260.

In southwest Puerto Rico, three northeast-ultramafic belts crop out: Monte del Estado peridotite belt (MEPB), Rio Guanajibo peridotite belt (RGPB), and the Bermeja Complex. Their protolith age is probably Late Jurassic or Lower Cretaceous. Although a number of studies have been made of these bodies, it is not understood whether or not they are all part of the one peridotite mass that has been dismembered. In this contribution we present new data about the mineralogy and mineral chemistry of the Monte del Estado and Rio Guanajibo serpentinized peridotites, which have revealed the presence of distinct groups of peridotites.

The Monte del Estado peridotite massif is the relatively large body to the north that is well exposed and accessible. The predominant rock type is spinel lherzolite with smaller amounts of diopside-bearing harzburgite. True dunites are absent. Both Opx and Cpx usually show kink-bands and undulatory extinction. The peridotite contains brownish aluminous spinel with Cr# = 0.12-0.16 and Mg# = 0.73-0.77. Olivine compositions fall in the range Fo_89-90, with NiO content between 0.28 and 0.52 wt%. Opx compositions are in the ranges En_85-90, with Al₂O₃ and Cr₂O₃ contents of 2.9-6.15 wt% and 0.26-0.79 wt% respectively. The Cpx Mg# ranges from 85 to 94. The Al₂O₃ content range from 2.5 to 6.5 wt%., Cr₂O₃ content from 0.33 to 1.11 wt%., and TiO₂ content from 0.17 to 0.53 wt%. In a Cr# vs. Fo diagram all analysed samples plot in the abyssal (ocean ridge) peridotite field.

The smaller Rio Guanajibo body was the subject of extensive investigations by Hess and others (Burk, C.A., (ed.), 1964.) A gravity survey associated with the 305-m-deep AMSOC core drilling project indicates that the RGPB is at least 2.8-km thick. Although much of the core is highly serpentinized and partly sheared, Mattson (1964) distinguished two lithologic rock types: diopside harzburgite and dunite that alternate through most of the core.

Based on the mineral chemistry we distinguish two types of peridotite in the RGPB. Group I peridotites (G1) are partially serpentinized and contain relic olivine, orthopyroxene and clinopyroxene. G1 peridotites show porphyroclastic textures with orthopyroxene usually showing kink-bands and undulatory extinction. They are predominantly spinel lherzolite and Cpx-rich harzburgite, as in the MEPB, and contain brownish aluminous spinel with Cr# = 0.14-0.16 and Mg# = 0.75-0.77, similar in composition to that of the MEPB. The Mg# of olivine is ~ 90, with NiO content between 0.39 and 0.43 wt%. Opx and Cpx compositions duplicate those of the MPEB. These mineral chemistries are similar to those of the peridotites from MEPB and to those of the most fertile abyssal peridotites, and do not seem to have been affected by a subduction component. In contrast, Group 2 peridotites (G2) are extensively serpentinized, but textural differences between mesh-texture lizardite and bastite indicate that most serpentinized peridotites were predominantly harzburgite. Their accessory Cr-spinel is Cr-rich, with Cr# = 0.72-0.74 and Mg# = 0.32-0.42. The compositions of the chrome spinel and olivine in the dunites are similar to those in the G2 peridotites. Their compositions and the presence of dunites resemble supra-subuction zone mantle peridotites (e.g. fore arc peridotites).

Our main conclusión is that the Rio Guanajibo peridotites are heterogeneous. MEPB peridotites and (G1) peridotites are refractory abyssal-type peridotites, within which there was no appreciable melting. This reflects the absence of dunites in the MPEB. Group (G2) corresponds to highly refractory peridotites comparable to those of supra-subduction zones, and might represent the pathway of arc-related melts in the mantle.

Giuseppina Kysar Mattietti¹, John F. Lewis², Michael R. Perfit³, George Kamenov³ James Mortensen⁴. Thomas Ullrich⁴and Richard Friedman⁴

(1)The George Mason University, Fairfax, Virginia, 22030, e-mail gkysar@gmu.edu (2) The George Washington University, Washington DC, 20052 (3) University of Florida, Gainesville, Florida, 32611 (4) University of British Columbia, Vancouver, Canada

Lewis et al (2005) reported that the granitoid samples dredged by Perfit and Heezen (1979) from the western north wall of the Cayman Trench, immediately southwest of the Rosario Bank area between 84.51°W and 84°54’W (Perfit and Heezen, 1979) showed a continental affinity. We have now analyzed 11 samples of the granitoids for major and trace elements, and Sr, Nd and Pb isotope compositions. The granitoid rocks range from 58% to 72% SiO₂ and are characterized by high concentrations of Th (up to 73.6 ppm in acid rocks), Zr ( 144-318 ppm), Nb (17-34.5 ppm), and LREE (La=34.7-128 ppm). Yitrium and HREE (Dy-Lu) concentrations are very low (Yb < 0.22-1.58 ppm). Ce/Yb ratios are high (121-287.5}. These values are more typical of continental arc granitoids and contrast with the oceanic island arc compositions of granitoids from the Greater Antilles islands including the Sierra Maestra of Cuba.

The most significant discriminants, though, are the isotopic compositions. 143Nd/144Nd ratios of 0.5124362-0.5125012 for the Cayman Trench granitoids are decidedly lower and corresponding 87Sr/86Sr ratios higher than for granitoids from the Greater Antillean islands and the Nicaraguan Rise. On a 143Nd/144Nd vs 87Sr/86Sr diagram the Cayman granitoid values fall in the field of continental crust and are close to the composition of the Bulk Earth. In addition Cayman Trench granitoids have Pb isotope compositions that are decidedly more radiogenic than granitoids from the Greater Antilles islands and granitoids drilled from Nicaraguan Rise, and that are consistent with the incorporation of an isotopically more evolved component such as continental crust or sea floor sediment. The values for 207/204Pb of !5.607-15.660 vs 206/204Pb of 18.830-18.965 are closely similar to the signature for lead isotopes of ore samples taken from basement and overlying volcanic rocks of the Chortis Block.

Cayman Trench granitoids have yielded satisfactory U/Pb ages on titanite and Ar/Ar ages on hornblende and biotite from 62 to 64 Ma with one biotite plateau age at 66.35 ± 0.34 Ma, slightly older than previous K/Ar determinations (Perfit and Heezen, 1979). These ages overlap those obtained for Late Cretaceous-Paleogene granitoid rocks intruding metamorphic rocks of the Chortis block of northern Honduras. On the other hand the ages and compositions for the Cayman Trench granitoids contrast with those of the Sierra Maestra of Cuba, considered to be an uplifted extension of the Cayman Ridge. Sierra Maestra granitoids yield U/Pb ages on zircon that range from 46.8 ± 0.2 to 60.5 ± 2.2Ma. Trace element plots of Sierra Maestra granitoids show geochemical signatures of oceanic arc or M-type granitoids. Pb isotope compositions lie along the MORB array and indicate a minimal subduction component. There have been no reliable dates of older than 60.5 Ma for granitoid rocks in the Sierra Maestra. On the other hand there have been no reliable dates younger than 62 Ma recorded for granitoid rocks from the NW Cayman Trench. Although volcaniclastic turbidites, of early Eocene age, similar to those in the Sierra Maestra, have been drilled (ODP Site 998) on the western Cayman Rise at 83°W, the crust underlying the western Cayman Ridge appears to include granitoid rocks with a distinct continental affinity, very different from the Sierra Maestra. The deeper crustal rocks of the western Cayman Ridge are likely to be a rifted eastern extension of the northern marginal basement complex of the Chortis block of Honduras, as has been suggested previously. It is concluded that the composition and Cretaceous-early Paleocene history of the western Cayman Ridge probably differed significantly from that of the Sierra Maestra. These data indicate the probability of three different, partly coeval, subduction-related magma systems in the NW Caribbean over the area of the NW Chortis block, the Sierra Maestra of Cuba and the northern Nicaraguan Rise during the interval 66 to 47 Ma.

(1) Dept. of Earth and Environmental Sciences, George Washington University, Washington, D.C. 20052. jlewis@gwu.edu

(2) Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí I Franquès, s/n, 08028 Barcelona, Spain. japroenza@ub.edu

The Loma Caribe peridotite forms the core of the Median Belt of Mesozoic age, in the central Dominican Republic. This belt includes two major metamorphosed units: (i) the Lower Cretaceous, Maimon Formation, with a bimodal suite composed of primitive island-arc tholeiite and rhyolite, to the north of the peridotite belt; (ii) the Upper Jurassic to Lower Cretaceous Duarte Complex, which have compositions comparable with oceanic plateau basalt, related to a mantle plume, to the south of the peridotite belt. The Loma Caribe peridotite is bounded by major faults (shear zones) within the body strike parallel to the northwest trend of the massif and to the foliation. Most of the ultramafic bodies consist of harzburgite, with clinopyroxene-rich harzburgite and minor amounts of lherzolite. Also, small bodies of dunite (up to 500 m in length and < 10 m across) have been mapped, particularly concentrated in the Loma Peguera, Loma Taina and Loma Guardarraya areas. Their contacts with harzburgite are mainly irregular, and are the same as the small irregular “patches” of dunite reported from the mantle section in many ophiolites complexes.

The Cr# in spinel from Loma Caribe peridotites vary from 0.20 (lherzolite) to 0.88 (dunite), indicating the occurrence of peridotites with very different melting histories. In terms of Cr-spinel composition, the Loma Caribe mantle peridotites can be divided into 3 groups:

Group I peridotites, which contain spinels with low Cr# [100Cr/(Cr + Al)] < 0.30 and low Fo [Mg/(Mg+Fe)] in olivine (avg. of Fo₉₀).

Group II peridotites contain spinels with intermediate Cr#s (0.30–0.65) and Fo in olivine (avg. of Fo₉₁).

Group III peridotites contain spinels with high Cr# (0.65–0.87) and high Fo in olivine (avg. of Fo₉₃). These peridotites concentrated in the Loma Taina, Loma Peguera and Loma Cumpié areas.

Group I peridotites plot in the abyssal peridotite field, whereas the highCr# in Cr-spinel, and very high Fo in olivine of group III peridotites suggest that they formed ashighly-depleted mantle residues. Their compositions are similarto those in harzburgite and dunite from forearc regions of subduction zones (e.g. Izu-Bonin-Mariana forearc peridotites). Group II peridotite field overlaps both the abyssal peridotite and the SSZ peridotite fields. Group I peridotites are enrichment in MREE and HREE compared to the groups II and III peridotites. Their REE pattern has low LREE/MREE and MREE/HREE ratios. On the other hand, the REE patterns of group II and III peridotites have homogeneous HREE contents and are characterized by relatively flat LREE and steep HREE fractionated segment. These patterns are similar to those of depleted peridotite from Mayarí-Baracoa peridotites in eastern Cuba, and to those of peridotite from Izu-Bonin-Mariana forearc.

The Loma Caribe peridotites represents a heterogeneous suboceanic mantle, which have mineral and whole-rocks compositions characteristic of mantle sections from both ocean basins and suprasubduction settings, and can be interpreted as residual mid-ocean ridge (Jurassic-Cretaceous protocaribbean oceanic lithosphere) accreted on the forearc mantle lithosphere related to Cretaceous Greater Antilles arc, similar to the South Sandwich forearc peridotites. In addition, this oceanic mantle probably was affected by a mantle plume (Duarte Plume). Restites for oceanic plateau basalt are peridotite contains chromian spinel with Cr# around 0.8, similar to Loma Peguera and Loma Taina dunites.

Uwe Martens¹, Christopher Mattinson², Joerg Geldmacher³, Hannes Brueckner⁴, J.G. Liou¹, Joseph Wooden¹.

Late Cretaceous continental collision of southernmost North America (the Maya Block) has long been recognized in the supracrustal record of northern Central America. This convergence can be straightforwardly linked with the metamorphic evolution of high-pressure belts of the Guatemala Suture Complex, because Campanian deepening of the Maya Block continental platform was contemporaneous with subduction and eclogitization of its Mesoproterozoic–Jurassic sialic basement (Chuacús Complex). Cpx-Grt-Phe thermobarometry of gneiss-hosted Chuacús eclogites indicate near ultra-high-pressure conditions at ~700–800 °C and ~2.1–2.4 GPa, implying continental subduction to >60 km depth. SHRIMP-RG in-situ dating of eclogite metamorphic zircon yielded a 75.5 ± 2 Ma age. Chondrite-normalized rare earth element patterns of zircon show depletions in heavy rare earths and lack Eu anomalies, consistent with a plagioclase-free, garnet-rich, eclogite-facies assemblage during zircon formation. Therefore, the Campanian age represents the timing of continental subduction, as confirmed by a 76 ± 16 Ma Sm/Nd mineral isochron of an eclogite band contained in orthogneiss.

Which Caribbean block collided with the Maya Block is disputed, but clues regarding the coliding terrane are given by the Maya Block's ubiquitous Upper Cretaceous flysch, which contains 75 ± 1 Ma volcanic cobbles (Ar/Ar on plagioclase). Trace element concentrations show that the cobbles were derived from a mature arc, suggesting that the hanging wall block was not the continental Chortis, in which no Late Cretaceous magmatism has been established, but the Great Antilles Arc, which is known to have been active then. Coeval arc volcanism in the Great Antilles and continental subduction of southernmost North America can be explained in terms of an oblique collision that diachronously closed the intervening ocean from west to east (zipper tectonics) as the Great Antilles migrated eastward toward the Bahamas platform.

Laboratorio de Arqueometría, Oficina del Historiador de Ciudad de La Habana (OHCH) ariadna@mail.org

Algunas gemas naturales, como el jade, pueden ser difíciles de identificar por los métodos tradicionales y su examen puede requerir del uso de equipamiento analítico avanzado. La información gemológica derivada de estos estudios (tales como: el espectro de absorción o los datos de composición química de las gemas) esta usualmente dispersa en la literatura científica y gemológica. En ocasiones, es necesario el análisis de difracción de rayos X (DRX) el cual identifica la fase cristalina de las piedras coloreadas o de las inclusiones minerales y suele efectuarse cuando existe suficiente cantidad de material disponible (análisis destructivo) para preparar una muestra en polvo mientras que el análisis por fluorescencia de rayos X (FRX) dispersiva en energía contribuye determinando los elementos químicos, los cuales pueden constituir las inclusiones que determinar el color o estar presente en la estructura de la fase cristalina. El análisis de objetos de arqueología únicos esculpidos en gemas requiere del desarrollo y combinación de métodos no destructivos (sin extracción de muestras) para la identificación del mineral. En la última década se han desarrollado y ampliamente aplicado espectrómetros portátiles de FRX que permiten el análisis elemental no destructivo e in situ de minerales sin embargo esta posibilidad no se ha extendido a los análisis de DRX de gemas; lo cual limita los estudios en los museos de objetos que por su valor, dimensiones o estado de deterioro no pueden ser trasladados del museo al laboratorio. En este trabajo se propone un método de análisis combinado DRX-FRX, a partir de modificaciones introducidas en un prototipo desarrollado de espectrómetro portátil de FRX, lo cual permite la identificación de gemas en objetos de arte y arqueología. Se ejemplifica con el estudio de la identificación de jade en ídolos Taínos (colección del Museo de Arqueología, de la OHCH) hallados en Cuba próximos al lugar donde actualmente se ha descubierto un yacimiento de jade. Este tipo de análisis abre nuevas perspectivas para el estudio de artefactos pre-colombinos de “probablemente” jade en las Antillas, de implicaciones en los estudios arqueológicos e históricos concernientes a las migraciones entre Mesoamerica y las antiguas Antillas.

Montes, C. ^(1,2), Cardona, A., ^(1,2), Bayona, G., ^(2,1), Farris, D., ⁽¹⁾, Strong, N., ⁽¹⁾, Morón, S., ⁽¹⁾, Rincón A., ⁽¹⁾, Silva, C., ⁽¹⁾

The Workshop "Suduction Zones of the Caribbean" seeks to unravel the complex geologic evolution of the Caribbean region focusing on deep earth processes taking place at ancient and active convergent plate margins. The main aim of the Workshop is the systematic characterization and comparison of subduction products, both mechanical and thermal, such as high-pressure belts, tectonic mélanges, accretionary wedges, accreted terranes, volcanic arcs, and fracture zones all along the Caribbean realm, northern South America and Nuclear Central America.

New data collected along northern Panamá and northwestern Colombia is integrated into a tectonic model for the Cenozic history of this margin. This model shows the effects of transpressional deformation driven by the migration of the subduction-related leading and trailing edges of the Caribbean plate along a margin where accretionary wedges, volcanic arcs, obducted oceanic crust and micro continental blocks interacted producing highly contrasting structural styles simultaneously. New data collected along this margin includes geochronology of detrital and magmatic zircons, trace and major element geochemistry of magmatic arcs in northern Panamá, paleomagnetic sites in the Santa Marta massif and central Panamá, geologic mapping in the Perijá range and central Panamá. Paleomagnetic investigations in Panamá (Silva et al., 2008) and the Santa Marta massif (Bayona et al., in review), and spatial distribution of magmatic arcs (Cardona et al., 2008) indicate that the micro-continental and oceanic blocks involved in the evolution of the margin have experienced vertical-axis rotation and large latitudinal translations. The paleomagnetic constrains are compared against new geochemical and geochronologic data in Panamá, the Plato-San Jorge basin in northern Colombia, as well as geologic mapping in the Perijá range and Ranchería basin (Montes et al., in review) and the Panamá Canal zone. This model preliminarily indicates that a moderate amount of vertical-axis clockwise rotation (17.3 ± 12.7 degrees) documented with paleomagnetic analyses in the Santa Marta massif, may explain as much as 105 km of extension (56%) along its trailing edge (Plato-San Jorge basin) and up to 42 km of shortening along its leading edge (Cesar-Ranchería basin). Neogene shortening in the Cesar-Ranchería valley is accommodated by the Cerrejón fault, a northwest-verging, crustal-scale fault that dips 9-12° to the southeast, thrusting Mesozoic onto Paleogene rocks, offsetting strata as young as early Eocene. Simultaneous extensional deformation is recorded in the fan-shaped Plato-San Jorge basin by a 2 to 6 km thick, shallowing-upward and almost entirely fine-grained Neogene sedimentary sequence that shows an increased subsidence rate at ca. 12 Ma. Large counterclockwise rotations of small blocks in the Panamá Canal area have been isolated and may record the initial closure of the isthmus and left-lateral deformation and generation of the Panamá orocline. This late shearing may be superimposed on predominantly normal faulting that characterizes the Panamá Canal area with mean NEE directions and diping to the south. The effects of the ENE translation of the Caribbean plate along this margin are thus integrated, showing a complex interaction of simultaneous right- and left-lateral shearing, extension and contraction and vertical-axis rotation.

Bayona, G., Jiménez, G., Silva, C., Cardona, A., Montes, C., Roncancio, J., in review, Paleomagnetic data uncovered from Mesozoic units of the Santa Marta Massif: constrain for paleogeographic and paleotectonic evolution of the NW corner of the South America plate: Journal of South American Earth Sciences

Cardona, A., Valencia, V., Reiners, P., Duque, J., Montes, C., Nicolescu, S., Ojeda G., Ruiz J., 2008, Cenozoic Exhumation of the Sierra Nevada De Santa Marta, Colombia: Implications on the Interactions Between the Carribean and South American Plate. Geological Society of America Anual Meeting, Houston.

Farris, D., Cardona, A., Montes, C., Morón, S., Bayona, G., Jaramillo, C., 2008, The Influence of the Panama Fracture Zone on Arc Magmatism. Geological Society of America Anual Meeting, Houston.

Montes, C., Guzmán, G., Bayona, G., Cardona, A., in review, Clockwise Rotation of the Santa Marta Massif and Simultaneous Neogene Deformation of the Plato-San Jorge and Cesar-Ranchería Basins: Journal of South American Earth Sciences

Silva, C., Bayona, G., Channel, J. T., Osorio, A., 2008, Block rotations and translations in the Isthmus of Panamá: American Gephysical Union Fall meeting, San Francisco.

Consulting Geologist, 2360 23^rd Street, Boulder, Colorado, 80304 USA E-mail: cnelson945@aol.com

A preliminary tectono-stratigraphic map of the Caribbean Basin was presented at conference on the origin of the Caribbean Plate held in Siguenza, Spain in May of 2006. In this preliminary map, all of the region’s country-scale maps were combined in a mosaic. Participants were invited then and are invited now to contribute their observations and interpretations to an evolving tectono-stratigraphic map of the Caribbean Basin. This poster session presents the map in its current form and provides an additional opportunity for conference participants to contribute. The goal is to produce a 1:2,500,000 scale tectono-stratigraphic map of the Caribbean Basin.

Kenya Núñez Cambra (1), Carlos Pérez Pérez (1), Enrique Arango Arias (2), José Rueda Pérez (3), Nicolás Vega Garriga (4), Arelis Núñez Labañino (1), Guillermo Millán Trujillo (1), Yamina Ríos Martínez (4), Ingrid Padilla Rodríguez (1).

1) Instituto de Geología y Paleontología. (IGP) kenya@igp.gms.minbas.cu; 2) Centro Nacional de Investigaciones Sismológicas del CITMA (CENAIS); 3) Filial Geomática Oriente de GEOCUBA IC; 4) Centro Nacional de Investigaciones Sismológicas - Holguín del CITMA (CENAIS).

La actual estructura tectónica de la región nororiental de Cuba es resultado del evento geodinámico más importante ocurrido en el noroeste caribeño, que comenzó en el Eoceno Medio tardío, dio lugar a la transcurrencia sinistral de la Falla Oriente, y afectó todo el territorio oriental, creando una estructura en bloques, con sistemas de fallas de dirección NE principalmente y NW, que se cortaron y desplazaron unos con respecto a otros, tanto horizontal como verticalmente. La distribución de las unidades geológicas muestra en superficie la dirección principal de los movimientos sinistrales en dirección NE. Los datos gravimétricos muestran continuidad en profundidad de estas estructuras casi verticalmente.

Estos esfuerzos horizontales desde el suroeste, reactivan las estructuras heredadas de momentos geodinámicos anteriores: el emplazamiento sobre el margen continental. Las evidencias sísmicas demuestran que se agudiza la actividad producto del infracorrimiento a través de la falla Norte de La Española. Esto complica aun más el modelo, con un esfuerzo proveniente del NE, que somete a la región nororiental a una presión, que reactiva los sistemas de fallas NW y NE, haciendo perceptible el movimiento horizontal dextral en la dirección NW (Falla Miraflores-Riíto), siguiendo su reflejo en los sistemas asociados a este con dirección NNW y NNE.

Los movimientos no se limitan al plano horizontal, producto de esfuerzos en sentido convergente, existen dentro de estos bloques mayores, estructuras compresivas con movimientos verticales ascendentes y en otros, movimientos descendentes con distensión asociada, limitados por fallas de tercer orden. Las mediciones de movimientos verticales recientes en la línea geodinámica de Moa confirman la existencia de diferentes bloques con tendencias específicas en su comportamiento espacio temporal, destacándose el bloque Miraflores con ascensos relativos promedio de hasta 60 mm en un año.

Las deformaciones tectónicas recientes y los terremotos originados en la región de estudio son consecuencia directa de la acumulación y liberación de tensiones derivada de la interacción actual de la placa de Norteamérica con el extremo oriental de Cuba. El modelo tectónico de la región de estudio muestra las principales estructuras a partir de la información geólogo-geofísica-geodinámica-sismológica recopilada. En el territorio emergido existen fallas activas como Miraflores-Riíto, Cayo Guam, Moa, Camarones, a las que se asocia actividad sísmica de moderada a baja energía y hasta 30 Km de profundidad.

Yamirka Rojas-Agramonte(1, 2), Alfred Kröner(1), James Pindell(3), Antonio García-Casco(4), Dora García-Delgado(5), Dunyi Liu(6), Yusheng Wang(6)

(1) Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany, (2) Departamento de Geología, Instituto Superior Minero Metalurgico de Moa, Las Coloradas, Moa, Holguín, Cuba, (3) Tectonic Analysis, Ltd., Cokes, Barn, West Burton, West Sussex RH20 1HD, U.K, (4) Departamento de Mineralogia y Petrología, Fuentenueva s/n, Universidad de Granada, 18002-Granada, Spain, (5) Centro de Investigaciones del Petróleo, Washington 169, Habana 12000, Cuba, (6) SHRIMP-Center, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, China.

Clastic sediments of the early (?) to late Jurassic (Oxfordian) San Cayetano Formation of western Cuba are interpreted to reflect syn-rift sedimentation coeval with the breakup of Pangaea. This sedimentary unit is the oldest known in the Guaniguanico Mountains and Cuba. U-Pb SHRIMP dating of 19 detrital zircon grains from two samples of San Cayetano micaceous sandstone provided concordant ages ranging from ~398 to 2479 Ma. The oldest zircon population is of Paleoproterozoic age (~2479-1735 Ma), but most zircons have early Mesoproterozoic and Grenvillian ages (~1556-985 Ma), whereas still younger ages are Pan-African (561 Ma), Ordovician (451 Ma) and early Devonian (~398 Ma). We discuss the possible origin of these zircons and conclude that the most likely source terrain(s) are Precambrian and early Paleozoic massifs in northern South America (Colombia and/or Venezuela) and the Yucatán Peninsula in Mexico. This is compatible with paleogeographic reconstructions of the Caribbean that imply that sediments of the San Cayetano Formation were still part of the disintegrating supercontinent Pangea in pre mid-Oxfordian time.

Y. Rojas-Agramonte(1,2,3); A. Kröner(1,2); M. Pérez(4); A. García-Casco(5); A. Fonseca-Montero(4); Dunyi Liu(2)

(1)Dept. of Geosciences, University of Mainz, 55099 Mainz, Germany, (2) SHRIMP Centre, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road Beijing 100037, China (3)Departamento de Geología, Instituto Superior Minero Metalurgico de Moa, Las Coloradas, Moa, Holguín, Cuba^.(4) Instituto Superior Politécnico José Antonio Echeverria, Avenida 114 No 11901 entre 119 y 127 , Marianao, codigo postal 19390, Habana , Cuba. (5)Departamento de Mineralogia y Petrología, Instituto Andaluz de Ciencias de la Tierra, Fuentenueva s/n, Universidad de Granada – CSIC, 18002 Granada, Spain.

The northern ophiolite belt (NOB) of Central Cuba consists of a mélange containing blocks of eclogite, garnet-amphibolite, amphibolitite, blueschist, greenschist, quartzite, metapelite, antigoritite and various types of intrusive rocks. Many of the granitoid varieties were interpreted as oceanic plagiogranites. We report SHRIMP U-Pb zircon ages and geochemical data for 8 unfoliated granitoid samples from the NOB in central Cuba. These samples were taken from blocks within serpentinite mélanges or intrude gabbro and diabase of the ophiolitic sequence. On the Geological Map of Cuba such rocks appear as elongated bodies with a main ESE-WNW trend, concordant with the foliation of the ophiolites. Chemically, these rocks are characterized by high SiO2 (63.6 to 74.3) and low to medium K2O (K2O = 0.21 - 2.54), and the Al-and Rb-contents are somewhat higher than in typical oceanic plagiogranites (Al2O3 = 14.15–16.32, Rb = 7.5 - 40.4 %); only two samples show a low Rb-content of 2.7 - 4.8 %. The Na2O, CaO and total iron contents range from 4.56-8.83, 0.58-3.23, and 2.77-4.27 respectively. The Rb vs (Y+Nb) diagram shows these granitoids to have volcanic arc affinity, and the AFM diagram reveals a calc-alkaline trend. Most samples have a metaluminous character with molecular ratio (mol. A/NK) between 1 and 2, whereas three samples have a peraluminous character. A trace element variation diagram normalized to Ocean-Ridge Granite (ORG) shows enrichment in highly incompatible elements, negative Nb anomalies and depletion in heavy REE, more typical of arc-related granitoids than oceanic plagiogranites.

A sample of trondhjemite from the the Cerro el Chivo area, S of Santa Clara, provided a concordant zircon age of ~86 Ma, whereas two peraluminous trondhjemitic samples taken from the Tres Guanos area S of Perea yielded zircon crystallization ages of ~72 and ~74 Ma. Rare Neoproterozoic and Permian inherited zircons are also present in these samples. A granodiorite and trondhjemite from the Las Bocas body, N of Placetas, yielded ages of ~75 Ma. These data constraint current geotectonic models for the region, because they indicate that emplacement of the ophiolite mélange must be younger than 72 Ma. Based on current geodynamic models for the region, our data suggest that the oceanic crust in the northern ophiolite belt is of supra-subduction type and is related to a volcanic arc domain during the late Cretaceous similar, perhaps to the tectonic setting of the Coast Range ophiolite in California. Therefore would represent fragments of the Caribbean plate and not the Proto-Caribbean lithosphere. Integration of geological data of the region suggests a fore-arc position. The occurrence of inherited zircons in two peraluminous samples may imply the involvement of subducted sediments containing an ancient zircon component because in some cases inherited zircons can survive in cool and dry peraluminous melts due to the low Zr saturation level in such magmas.

Department of Geography and Geology, University of the West Indies, Mona, Kingston 7,

Rift basins form through crustal extension, and are frequently associated with tectonic deformation. Two such rift basins, Wagwater and John Crow Mountain Troughs, are present in Jamaica and formed in the Maastrichtian-Paleocene due to the interaction of the Caribbean Plate with the North American Plate. These two basins have been inverted and their sedimentology and rift basin evolution are presented. This paper provides insight in to the past, current and ongoing work on the sedimentary successions in these basins and uses these to constrain a new model for the evolution of the northern margin of the Caribbean Plate that has recently been developed. Geological maps and logged representative sedimentary sections are presented. The succession in the John Crow Mountain Belt comprises the Bowden Pen Formation (Late Maastrichtian to earliest-Danian) and represents a sequence of poorly sorted syn-rift conglomerates and sandstones deposited in submarine fans reflecting an early phase of basin development. This is succeeded by the rift-filling siliciclastic turbiditie-mudstone sequence of the Moore Town Formation deposited in a deep-water setting during the Late Maastrichtian to Early Paleocene. Four lithofacies are recognized in the formation, three of which are characterized by diverse ichnofossils. The three distinctive lithofacie-ichnofacies associations indicate deposition in an abyssal marine to mid/distal continental shelf to nearshore shelf. Post-rift deposition is marked by a change to carbonate deposition (Nonsuch Formation) in the late Paleocene and marks the cessation of uplift on the rift’s margins and westward migration of rifting to the Wagwater Trough.

The Wagwater Belt consists of at least 6 km Tertiary succession of coarse-grained, terrigenous, dominantly terrestrial strata, overlain by about 2 km of upward-fining marine sandstones and impure limestones (Wagwater Formation). This is succeeded by the laterally more extensive, Richmond Formation; deep marine turbidites with microfauna and two distinctive lithofacies-ichnofacies associations indicative of an early Eocene age and deposition at sublittoral to bathyal depths, representing primarily as distal submarine fan deposits.The use of new available biostratigraphy and radiometric ages, and newly generated geochemical analyses of volcanic rocks, within the Wagwater Belt are presented.

J. Tait(1), Y. Rojas-Agramonte(2,3), D. García-Delgado(4), A. Kröner(5), R. Pérez-Aragón(6)

(1) School of Geosciences, University of Edinburgh, EH9 3JW, UK (2) Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany, (3) Departamento de Geología, Instituto Superior Minero Metalurgico de Moa, Las Coloradas, Moa, Holguín, Cuba, (4) Centro de Investigaciones del Petróleo, Washington 169, Habana 12000, Cuba, (5) Instituto de Geologia y Paleontologia, Ciudad de la Habana, Cuba

A detailed palaeomagnetic study of Cretaceous age volcanic and sedimentary arc rocks from central Cuba has been carried out. Samples from 32 sites (12 localities) were subjected to detailed demagnetisation experiments. Nineteen sites from the Los Paso, Mataguá, Provincial and Cabaiguán Formations yielded high unblocking temperature, dual polarity directions of magnetisation which pass the fold tests with confidence levels of 95% or more and are considered to be primary in origin. The palaeomagnetic inclinations are equivalent to palaeolatitudes of 9°N for the Aptian, 17°N for the Albian. A synfolding remanence identified in 5 sites from the younger Hilario Formation indicates a late Cretaceous remagnetisation at a palaeolatitude of 15°N. Our results are in good agreement with previous palaeogeographic models and provide the first high quality palaeomagnetic data demonstrating the gradual northward movement of the Cretaceous Volcanic Arc throughout the Cretaceous. The declination values obtained all indicate significant and similar amounts of anticlockwise rotation from the oldest sequences studied through to the late Cretaceous remagnetisation. This rotation is most likely related to collision of the arc with the North American plate and transpressional strike slip movement along the northern margin of the Caribbean plate as it progressed eastwards into the large Proto-Caribbean basin.

Tobón, M. ⁽¹⁾, Weber, M.⁽¹⁾, García-Casco, A.^(2,3⁾, Cardona, A.⁽⁴⁾, Valencia, V. A. ⁽⁵⁾

(1) Escuela de Geociencias y Medio Ambiente, Universidad Nacional de Colombia, calle 65 #78-28, bloque M1, of.414, Medellín, Colombia. E-mail: monicatobon@gmail.com. (2) Departamento de Mineralogía y Petrología, Universidad de Granada, Avda Fuentenueva sn, 18002, España. E-mail: agcasco@ugr.es (3) Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Avda. Fuentenueva s/n, 18002 Granada, Spain. (4) Smithsonian Tropical Research Institute, Panamá. (5) Department of Geosciences, University of Arizona, USA.

Eclogite and high pressure metasedimentary rocks have been found in a Miocene conglomerate in the northernmost Colombian Caribbean region. These rocks are major records of the convergence tectonics of the southern margin of the Caribbean plate. A detailed petrologic study was carried out on a kyanite–rutile–clinozoisite-bearing garnet– phengite–quartz schist in order to reconstruct its metamorphic evolution and to constrain the subduction/accretion physical parameters within this region. Metamorphic P-T conditions were determined with the average P-T method with the Thermocalc program. The peak metamorphic assemblage (phengite + paragonite + kyanite + garnet) equilibrated around 600° C and 20 + 3 kbar. A Pseudosection calculated for the NCKFMASH system for the bulk composition suggests two possible P-T paths (Figure 1). The decompression trajectory of this rock indicates that exhumation followed an apparent clockwise P-T path typical for “Alpine-type” subduction zones. Recurring events of garnet growth and dissolution previous to the attainment of metamorphic peak conditions suggest that the rock underwent subtle fluctuations in P-T during the prograde trajectory that could be related to the instability of subduction and initiation of collision. P-T paths, U/Pb detrital zircon patterns, and Campanian Ar-Ar mica cooling ages suggest that this sample record the collision between the South American margin and the Caribbean arc.

Figure 1. P-T pseudosection for a quartz-phengitic schist (sample CM 411) from Serranía de Jarara, Guajira Peninsula, Colombia in the system NCKFMASH (+ q + H₂O). The bulk composition of the rock is SiO₂ = 70.71, Al₂O₃ = 14.72, CaO = 1.56, MgO = 1.54, FeO = 3.97, K₂O = 3.12, Na₂O = 1.22 like weight percent. The heavy and dotted lines are the proposed trajectories for the rock.

Department of Geological Sciences, C1100, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, USA. E-mail: esti.ukar@gmail.com

The Franciscan Complex forms the structurally complicated, locally chaotic basement of Northern and Central California and southwestern Oregon Coast Ranges. It is an accretionary wedge formed related to the Jurassic-Tertiary subduction along the west coast of North America (e.g. Hamilton, 1969). In northern California, the Franciscan is subdivided into three belts, the Western, Central, and Coastal belts, which show a zonation in age, metamorphic “grade”, and structural style (Bailey et al., 1964; Ernst, 1973). Franciscan mélanges are found along the Central belt, as well as the Diablo Range -a tectonic window within the overlying Great Valley Group-, and the Nacimiento Block, where the study area is located.

One of the best exposures of Franciscan Mélange, where contact relationships between blocks and matrix can be observed, is found along 6 km of seacliffs near San Simeon. Boudinaged blocks of graywacke, greenstone, chert, and rarer blueschist and graphite-schist are dispersed in the shale matrix. Block sizes range from 10 cm to 15 m. The discovery of interlayered blueschist and graphite-schists, and the presence of lawsonite in some graphite-schists revealed these two lithologies are genetically related.

Two main mineral assemblages were recognized among the studied 34 mafic blueschist blocks: 1) Lws + Na-amp + Chl + Pmp + Phen, recrystallized at 7-9 kb and 250-350°C, and 2) Lws + Na-amp + Ep + Chl + Pmp + Phen, formed under higher temperatures (350-375°C). A pre-blueschist facies metamorphic event under lower-P and equal or higher-T conditions is recorded by calcic cores overprinted by Na-amp rims in half of the blocks. Rims with a higher Fe³⁺ content probably developed due to the breakdown of Ep during a decrease in T.

Graphite-schist blocks (30 studied) contain qtz + mus + plag + graph, and are of two types. One type (13 blocks) has relict sedimentary textures with a weak foliation defined by graphite and pressure solution seams. The other type (17 blocks) has a compositional layering with layers containing well recrystallized quartz. Nine of these blocks also contain lawsonite within the more graphitic layers.

The geochemistry of the blueschist blocks suggests they were derived from the MORB-like oceanic crust of the hanging wall, and seamounts underplated during the initiation of subduction. The mainly mafic protolith contained a small volume of interlayered sediment, as indicated by the presence of associated metasedimentary graphite-schists. Blueschist facies conditions were attained at the bottom of the overriding plate during the initial states of Franciscan subduction. Blocks were plucked from the bottom of the hanging wall, incorporated into the subduction-channel, and exhumed due to the upward flow driven by the movement of the downgoing plate. Incorporation of graphite-schist-like sediment into the subduction zone probably continued well after blueschist facies conditions were attained.

Bailey, E. H., Irwin, W. P., and Jones, D. L., 1964, Franciscan and related rocks, and their significance in the geology of western California: California Division of Mines Geological Bulletin, v. 183, p. 89-112.

Ernst, W. G., 1973, Blueschist metamorphism and P-T regimes in active subduction zones: Tectonophysics, v. 17, p. 255-272.

Hamilton, W., 1969, Mesozoic California and the underflow of Pacific mangle: Geological Society of America Bulletin, v. 80, p. 2409-2430.

Weber, M.⁽¹⁾, Cardona, A.⁽²⁾, Valencia, V. A. ⁽³⁾, Garcia-Casco, A.⁽⁴⁾, Altenberger, U.⁽⁵⁾, Zapata, S.⁽¹⁾, Tobón, M. ⁽²⁾

(1) Escuela de Geociencias y Medio Ambiente, Universidad Nacional de Colombia, Sede Medellín. mweber@unal.edu.co

New geochronological, geochemical and petrological data from magmatic and metamorphic units in northernmost Colombia record the Late Cretaceous interactions of the Caribbean arc and the South American margin.

The Cabo de la Vela mafic-ultramafic complex comprises a Campanian intra-oceanic arc of older ultramafic and gabbroic units with back-arc signatures intruded by younger arc rocks.

U/Pb zircon provenance patterns from Campanian high-pressure rocks found as boulders in Miocene conglomerates and in-situ lower-grade schists indicate a predominantly South American margin source, with limited contemporaneous arc input. Geothermobarometry data indicate complex Alpine type P-T-t paths for the high-pressure rocks.

The spatial and temporal data for these rocks can be related to the collision of an intra-oceanic arc and back-arc against the passive continental South American margin.

The lack of extensive arc remnants and the direct juxtaposition of back-arc remnants against the metamorphosed continental margin suggest that most of the arc was almost completely subducted, probably as a consequence of the failure of the extinct back arc spreading centre as predicted by existing thermo-mechanical models (Boutelier et al., 2003).

The sealing of the accretion is possibly recorded in the Maastrichian ages found in the Neogene sediment cover, which correlates with ages from a nearby post-tectonic type granite.

Boutelier, D., Chemenda, A., Burg, J-P., 2003. Subduction versus accretion of intra-oceanic volcanic arcs: insight from thermo-mechanical analogue experiments. Earth and Planetary Science Letters. 212, 31-45.

NUEVOS CRITERIOS ACERCA DE LAS CARACTERISTICAS SISMOGEODINAMICAS DEL EXTREMO NORORIENTAL DE CUBA.

FROM THE “HISPANIC CORRIDOR” TO THE CARIBBEAN SEAWAY: PLATE TECTONICS AND PALEOCEANOGRAPHY OF THE MESOZOIC TETHYS – PROTO-CARIBBEAN CONNECTION

LA SUTURA SEPTENTRIONAL EN CUBA CENTRAL

P-T PATHS OF AMPHIBOLITE BLOCKS FROM LA COREA MELANGE (EASTERN CUBA).

THERMAL EVOLUTION, AGE AND TECTONIC IMPLICATIONS OF LA COREA MELANGE (EASTERN CUBA).

THE COMPOSITION OF CHROMITE FROM SERPENTINITES IN LA COREA MÉLANGE (EASTERN CUBA): A RECORD OF FORE ARC PERIDOTITES IN THE SUBDUCTION COMPLEX.

PETROGRAPHIC AND GEOCHEMICAL CHARACTERISTICS OF JADEITITE JADE FROM THE SIERRA DEL CONVENTO SUBDUCTION MELANGE (EASTERN CUBA).

FORMATION OF GRANITOID CRUST IN ISLAND ARC SETTINGS: INSIGHTS FROM CENTRAL-WESTERN PANAMA

COASTAL CRETACEOUS METAMORPHIC COMPLEXES OF THE SIERRA NEVADA DE SANTA MARTA: A RECCORD OF COLLISION AND SUBDUCTION

GEOCHEMISTRY AND AGE OF AMPHIBOLITES AND GRANITIC-GNEISSIC ROCKS OF THE MABUJINA COMPLEX AND OF THE MANICARAGUA BATHOLITH (CENTRAL CUBA).

PALEOCENE ─ MIDDLE EOCENE EVENTS IN CUBA. CONSTRAINS FOR THE CARIBBEAN ― NORTHAMERICAN PLATES BOUNDARY HISTORY.

CORTEZA TERRESTRE PROFUNDA EN EL CARIBE OCCIDENTAL (I): REGIONALIZACIÓN DE LOS CAMPOS GRAVIMÉTRICO, ISOSTÁTICO Y MAGNÉTICO EN CUBA

ESTRUCTURA GEOLÓGICA Y FASES DE DEFORMACIÓN EN EL ÁREA LA SIERRITA, CÚPULA DE TRINIDAD, MACIZO ESCAMBRAY, CUBA CENTRAL.

METAMORFISMO DE ALTA PRESIÓN DE LAS ROCAS DE FACIE ESQUISTOS VERDES EN EL MACIZO ESCAMBRAY. EVIDENCIAS DE SUBDUCCIÓN Y ACRECIÓN DURANTE EL CRETÁCICO TARDÍO EN LA PLACA CARIBE.

THE SANTA MARTA BATHOLITH: A COMBINED RECORD OF PALEOGENE COLLISION AND ONSET OF THE CARIBBEAN PLATE SUBDUCTION BENEATH THE NORTHERN MARGIN OF THE SOUTH AMERICAN PLATE.

MESOZOIC TO EOCENE PLATE TECTONIC OF THE CIRCUM PACIFIC AREA: NEW CONSTRAINTS ON FAR TRAVEL EXOTIC TERRANES, SUBDUCTION ZONE MELANGES AND ARC-ARC COLLISIONS.

PROPOSAL FOR THE DECLARATION OF GEOLOGICAL HERITAGE FOR A BLOCK OF ECLOGITE, SANTA CLARA PROVINCE, CUBA

A NEW JADEITITE JADE LOCALITY (SIERRA DEL CONVENTO, CUBA): FIRST REPORT AND SOME PETROLOGICAL AND ARCHAEOLOGICAL IMPLICATIONS.

JADEITITES IN THE CARIBBEAN CONTEXT: RECORDERS OF TECTONIC PROCESS, SUBDUCTION FLUID COMPOSITION AND PRE-COLUMBIAN CULTURAL CONNECTIONS

MINERALOGY AND MINERAL CHEMISTRY OF THE MONTE DEL ESTADO AND RIO GUANAJIBO PERIDOTITES, SW PUERTO RICO

Granitoids with a continental affinity from the NW wall of the Cayman Trench: Implications for Subduction Zone magmatism in the Cayman, Sierra Maestra, N Chortis Block and Nicaraguan Rise

COMPOSITIONAL HETEROGENEITY IN LOMA CARIBE MANTLE PERIDOTITES, DOMINICAN REPUBLIC: A RESULT OF SUBDUCTION-MANTLE PLUME INTERACTION?

LATE CRETACEOUS CONTINENTAL SUBDUCTION OF NORTH AMERICA'S SOUTHERNMOST BASEMENT

IDENTIFICACIÓN NO DESTRUCTIVA DE JADE EN OBJETOS ARQUEOLÓGICOS: ESTUDIO DE IDOLILLOS DE ABORÍGENES TAÍNOS

TECTONIC RECONSTRUCTION OF THE PANAMA-NW COLOMBIA MARGIN: NEW CONSTRAINTS FROM GEOLOGICAL MAPPING, GEOCHRONOLOGY, GEOCHEMISTRY AND PALEOMAGNETISM

A TECTONO-STRATIGRAPHIC MAP OF THE CARIBBEAN BASIN – A PROGESS REPORT

NUEVOS APORTES A LA ESTRUCTURA TECTÓNICA Y GEODINAMICA DE LA REGION NORORIENTAL DE CUBA

DETRITAL ZIRCON GEOCHRONOLOGY OF THE SAN CAYETANO FORMATION: IMPLICATIONS FOR THE JURASSIC PALEOGEOGRAPHY OF THE NW PROTO-CARIBBEAN

GEOCHEMISTRY AND SHRIMP ZIRCON AGES OF GRANITOID ROCKS FROM THE NORTHERN OPHIOLITE MÉLANGE OF CENTRAL CUBA

RIFT BASINS IN JAMAICA: SEDIMENTARY ARCHITECTURE AND BASIN DEVELOPMENT

PALAEOMAGNETISM OF THE CENTRAL CUBAN CRETACEOUS ARC SEQUENCES AND GEODYNAMIC IMPLICATIONS

PRESSURE-TEMPERATURE AND TIME CONSTRAINS FOR HIGH PRESSURE METASEDIMENTARY ROCKS FROM NORTHERNMOST COLOMBIA – CARIBBEAN REGION

BLUESCHIST AND ASSOCIATED GRAPHITE-SCHIST BLOCKS IN THE FRANCISCAN MELANGE, SAN SIMEON, CALIFORNIA

LATE CRETACEOUS TECTONIC INTERACTIONS BETWEEN THE SOUTH AMERICAN PLATE AND THE CARIBBEAN ARC: INSIGHTS FROM THE MAGMATIC AND METAMORPHIC RECORD OF THE GUAJIRA REGION, NORTHERN COLOMBIA