Images source: Modified after Iturralde-Vinent, M.A. 1998. Sinopsis de la constitución geológica de Cuba. Acta Geológica Hispánica 33, 9-56.

The terrane is composed of an ensemble of strongly deformed tectonic slices that comprise continental margin metasediments and metaophiolites (Somin and Millán, 1981; Millán and Somin, 1985; Millán, 1997b; Stanek et al., 2006).

Image source: Modified by García-Casco et al., 2006 after Millán, 1997b. Geología del macizo metamórfico del Escambray. In: Furrazola Bermúdez, G.F., Núñez Cambra, K.E. (eds.). Estudios sobre Geología de Cuba. La Habana, Cuba, Centro Nacional de Información Geológica, 271-288, with indication of major tectonic units, serpentinite mélanges and amphibolite and eclogite bodies.

 
Image sources: García-Casco et al., 2006. High pressure metamorphism of ophiolites in Cuba. Geologica Acta 4, 63-88; Schneider et al., 2004. Origin and evolution of the Escambray Massif (central Cuba); an example of HP/ LT rocks exhumed during intraoceanic subduction. Journal of Metamorphic Geology, 22, 227-247; and Stanek et al., 2006. Structure, tectonics and metamorphic development of the Sancti Spiritus Dome (eastern Escambray massif, Central Cuba). Geologica Acta 4, 151-170)

P-T conditions during metamorphism in the Escambray were variable (Millán, 1997b; Stanek et al., 2006), ranging from low grade at intermediate-P (greenschist facies) and high-P (blueschist facies) to medium grade at high-P (eclogite facies). The internal deformation is intense and complex, with numerous tectonic-metamorphic inversions. The massif has an inverted metamorphic zoning, with greenschist facies at the base in unit I, greenschist and lawsonite blueschist facies in unit II, and epidote-blueschist and eclogite facies at the top in unit III. The uppermost unit IV in contact with the overlying Mabujina complex diverges from this pattern (greenschist-blueschist facies). High pressure conditions indicate subduction of the continental margin. Subduction of oceanic lithosphere is also documented by serpentinite matrix mélanges bearing high-pressure exotic blocks. Available age data range from Upper Jurassic (U-Pb age of zircon in eclogite, Maresch et al., 2003) through mid-Cretaceous (U-Pb: 106-100 Ma; Hatten et al., 1988, 1989) to Upper Cretaceous (K-Ar: 85-68 Ma; 40Ar/39Ar: 71-68 Ma; Rb/Sr: 65-69 Ma; Somin and Millán, 1981; Hatten et al., 1988; Somin et al., 1992; Iturralde et al., 1996; Schneider et al., 2004). Except for the Upper Jurassic age (discussed below), these ages are consistent with subduction in the course of the Upper Cretaceous and exhumation during the late Upper Cretaceous. This suggests that the associated subduction system may be independent of the Lower Cretaceous subduction system recorded in the HP blocks of mélanges from the northern ophiolite belt in western and central Cuba. Petrologic evidence presented by García-Casco et al. (2006) supports this view.

Millán (1997b) and Schneider et al. (2004) identified blueschist retrogression of eclogite facies rocks of tectonic unit III as a result of syn-subduction exhumation during the late Upper Cretaceous. These authors also noted that the prograde metamorphic evolution of coherent eclogite samples present in the metasedimentary formations is more complex than that of the eclogite blocks of the tectonically intercalated strips of serpentinite-mélanges, but that their peak eclogite conditions and retrograde evolutions are similar, the latter characterized by substantial cooling upon exhumation. Age data for an eclogite block within a serpentinite-mélange body from unit III  are 40Ar/39Ar (phengite): 69.3±0.6, 40Ar/39Ar (barroisite): 69.1±1.3 and Rb/Sr (whole rock-phengite-barroisite): 66.0±1.7 Ma(Schneider et al., 2004). These figures are interpreted as cooling ages close to thermal peak. The sample is made of a peak mineral association is composed of almandinic (type-C) garnet, sodic-calcic (barroisite) amphibole, omphacite, epidote, phengite, quartz, rutile and apatite, which is typical of amphibole-eclogites. Garnet porphyroblasts include epidote, sphene, rutile, amphibole, omphacite and quartz. These inclusions are oriented along an internal foliation oblique to the external foliation. Garnet zoning is concentric, typical of prograde growth, with cores richer in Fe, Mn and Ca, and rims richer in Mg and Mg#. This zoning pattern is disturbed by mechanical rupture of grains during deformation before attainment of the metamorphic peak. The primary assemblage is irregularly replaced by a post-kinematic retrograde assemblage consisting of actinolite, glaucophane, albite, (clino)zoisite and chlorite, indicative of blueschist facies conditions. Small grains of glaucophane overprint prograde barroisite, omphacite and garnet. At sites where glaucophane grew adjacent to garnet, its composition is richer in Fe and Al, while it is richer in Mg at sites dominated by amphibole and/or omphacite, indicating diffusion problems during retrogression.

P-T paths are clockwise, with prograde sections within the eclogite field followed by strong cooling during decompression. That the retrograde P-T path involves substantial cooling, as is typical for Franciscan-type paths, is indicative of a low geothermal (i.e., refrigerated) gradient during exhumation, implying that subduction did not stop during late Cretaceous mélange formation and exhumation. This scenario appears to contradict the thermal-tectonic evolution of the early Cretaceous subduction zone where the blocks contained within serpentinite mélanges from the northern ophiolite belt in western-central Cuba were metamporphosed.