· Eastern Cuba: Onset of subduction during the mid-Cretaceous

High Pressure Metamorphism in eastern Cuba (see García-Casco et al., 2006, García-Casco, A., 2007, García-Casco et al., 2008 for details and complete references).


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

 Location of subduction mélanges in eastern Cuba. They appear within the eastern ophiolite bodies.


Image source: Pushcharovsky, Y. (Ed.) 1988. Mapa geológico de la República de Cuba escala 1:250 000, Academias de Ciencias de Cuba y la URSS (Geologic Map of the Republic of Cuba Scale 1:250000, Academies of Sciences of Cuba and the USSR). Modified by A. García-Casco.


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

 Eastern Cuba extends towards the East from the Nipe fault. The huge Mayarí-Cristal and Moa-Baracoa ophiolite bodies of this region have been classically viewed as the eastern counterpart of the northern ophiolite belt, but Iturralde-Vinent et al. (2006) have characterized them as “eastern ophiolites”. These bodies have been considered as suprasubduction ophiolite that underwent widespread infiltration by melts of island arc tholeiitic and boninitic composition that interacted with the ultramafic rocks (Proenza et al., 1998, 1999; Gervilla et al., 2005). The region contains a number of volcanic arc formations having distinct island arc tholeiitic, boninitic and calc-alkaline signatures, though in most cases they appear to be of Upper Cretaceous age (Iturralde-Vinent et al., 2006; Proenza et al., 2006). Whether these geochemically distinct arc volcanics formed within a single or different subduction zones is uncertain. The Purial volcanic complex, south of the ophiolitic bodies, includes island arc tholeiitic and calc-alkaline signatures and has been classically considered the eastern prolongation of the Cretaceous arc belt of western-central Cuba (Iturralde-Vinent, 1996c). However, important geological contrasts with other parts of Cuba are that this Cretaceous volcanic arc terrane is a) tectonically overridden by the ophiolitic complexes and b) metamorphosed to the greenschist and blueschist facies (Boiteau et al., 1972; Cobiella et al., 1977; Somin and Millán, 1981; Millán et al., 1985). Importantly, metamorphism in this complex is dated as late Upper Cretaceous by Somin et al. (1992; 75 ± 5 Ma K-Ar whole-rock) and Iturralde-Vinent et al. (2006; 75-72 Ma based on paleontological arguments). The Mesozoic North American margin (Florida-Bahamas platform) has been commonly identifed in this region by the sedimentary sequences of the Asunción terrane, though an exotic origin cannot be excluded. This complex is metamorphosed to high-P low-T conditions (Millán et al., 1985). Regionally, the ophiolite bodies override the Asunción metasediments. The major displacements appear to be NE to NW-directed thrusts (Cobiella et al., 1984; Quintas, 1987, 1988; Nuñez Cambra et al., 2004). However, the structure of the region is complex and has not been studied in detail.


Image sources: García-Casco, 2005, García-Casco, 2007, García-Casco et al., 2008 and A. García-Casco, unpublished.

 The ophiolitic bodies of eastern Cuba include serpentinite-matrix mélanges containing high-pressure blocks.The largest complexes are La Corea and Sierra del Convento mélanges, both having similar lithological assemblages (Millán, 1996a). La Corea mélange is located in Sierra de Cristal and is associated with the Mayarí-Cristal ophiolitic body. The Sierra del Convento mélange, located southward, overrides the Purial metavolcanics. The nature of the metamorphic blocks is varied but, in contrast with other mélanges from central and western Cuba, high temperature epidote±garnet amphibolites bearing small bodies of leucocratic (mostly trondhjemitic) material dominate. Other types of block are blueschist, greenschist, quartzite, metagreywacke and metapelite, while eclogite is rare (Cobiella et al., 1977; Somin and Millán, 1981; Kulachkov and Leyva, 1990; Hernández and Canedo, 1995; Leyva, 1996; Millán, 1996a). Available age data for HP rocks range from 125 to 66 Ma in La Corea and 116-82 Ma in Sierra del Convento (Adamovich and Chejovich, 1964; Somin and Millán, 1981; Somin et al., 1992; Iturralde-Vinent et al., 1996; Millán, 1996a). As in central and western Cuba, the recurrence of Early Cretaceous ages indicates Early Cretaceous subduction. However, the geological singularities of eastern Cuba make the correlation of the associated subduction systems doubtful. These doubts are strengthened by the petrologic differences of the metamorphic blocks from both regions, as described below.

The most typical rock type of eastern Cuba mélanges is epidote-amphibolite, commonly bearing garnet. The prograde assemblage consists of calcic (pargasitic) amphibole, epidote, garnet, sphene, rutile and apatite. Quartz is also common. Prograde plagioclase is lacking, as in most metabasite samples metamorphosed to the epidote-amphibolite facies of the Sierra del Convento mélange, suggesting relatively high pressure of formation. Retrograde overprints consist of albite, actinolite, glaucophane, chlorite and pumpellyite. Pargasitic amphibole comprises most of the matrix and is oriented parallel to the foliation. Individual crystals have a smooth core-to-rim prograde zoning. The rims are commonly partly replaced by actinolite, glaucophane, chlorite and albite. Epidote displays a faint patchy zoning. Garnet forms large porphyroblasts (up to >1.5 cm in diameter) that include pargasitic amphibole, epidote, rutile and sphene, and is slightly replaced at the rims and along fractures by pargasite-magnesiohornblendeactinolite, chlorite, pumpellyite and albite. Its composition is rich in almandine and grossular and the grains bear a smooth prograde growth zoning with decreasing Mn and increasing Mg# towards the rims. The outermost 200-300 µm of the grains may display reverse diffusive zoning (noted by upturns in Mg# and Mn) formed during retrograde exchange with the matrix. This type of zoning indicates relatively high temperature at the onset of retrogression. Importantly, oscillatory zoning has not been observed in garnet from amphibolites of the Sierra del Convento mélange.

The P-T paths are counterclockwise, with high-grade conditions attained during subduction and blueschist conditions attained during accretion and exhumation. P-T conditions of the pre-peak and peak assemblages are 600-650ºC and 14-16 kbar, and 750-800ºC and 15-18 kbar respectively.

These findings, which indicate hot subduction and cold exhumation for the amphibolite blocks of eastern Cuba mélanges, contrast with P-T conditions and paths observed in blocks from mélanges in western-central Cuba. Thus, the Early Cretaceous subduction systems of the two regions either were different or were associated with different geodynamic scenarios. Indeed, hot-subduction can be rationalized within the framework of either a) initiation of subduction or b) subduction of young oceanic lithosphere or an active oceanic ridge (Oh and Liou, 1990; Wakabayashi, 1990, 2004; Gerya et al., 2002; Willner et al., 2004). In the first case, the mélanges of eastern Cuba document initiation of a new subduction system during the mid-Cretaceous simultaneously with termination of subduction in central and western Cuba. In the second case, the mélanges of western-central and eastern Cuba were generated within the same Early Cretaceous subduction system, but a triple junction interaction (ridge-trench-transform or trench-transformtransform,
Wakabayashi, 2004) should have occurred at its eastern branch. An important constraint that may contribute to solving this problem is the progressively refrigerated system implied by the observed retrograde paths in the high-grade blocks from eastern Cuba mélanges, which is consistent with continued subduction during incorporation of the blocks into the associated overlying subduction channel. This mechanism is not consistent with the mid-Cretaceous arrest of subduction inferred for western-central Cuba, favoring the “initiation of subduction scenario” for eastern Cuba and, consequently, the lack of correlation between the subduction systems of both regions.

last modified: 01.07.08 16:02 +0100