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

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

Central Cuba is used informally to embrace the area from Havana to Holguín (from the Pinar fault to the West, to the Nipe fault to the East) which bears the most complete representation of geologic complexes in the island. In this region, the continental North American margin and foreland to the north includes middle Jurassic to Eocene sedimentary formations of Cayo Coco, Remedios, Camajuaní and Placetas belts, of which the latter is of deep water affinity and related to the oceanic Proto-Caribbean realm (Iturralde-Vinent, 1996a, 1998). The northern ophiolite belt is formed by a number of tectonic slices thrusted northward and partially intermingled with the Placetas belt. To the south, the Cretaceous volcanicplutonic arc belt is tectonically emplaced above the northern ophiolite belt, but in the Havana-Matanzas and Holguín regions it is tectonically intermingled with the northern ophiolites. The Cretaceous volcanic arc belt contains Neocomian?-Albian tholeiitic rocks covered by Albian-Campanian calc-alkaline and high-alkaline rocks. The suites are formed by volcanic, plutonic and volcanicsedimentary sequences. The volcanic-arc units tectonically overlie the Mabujina complex, composed mainly of arc-derived medium- to high-grade, low to intermediate pressure, metamorphic rocks of ultrabasic, basic, intermediate and acid composition that are crosscut by slightly to strongly metamorphosed and deformed plutonic bodies (Somin and Millán, 1981; Millán, 1996b; Grafe et al., 2001; Blein et al., 2003). This complex is interpreted as the metamorphosed roots of the island arc and its oceanic sole (Somin and Millán, 1981; Millán, 1996b) or as a separate arc system (Blein et al., 2003). The Mabujina complex is in turn tectonically underlain by the Escambray terrane, described below. The thrust-and-fold belt was complexly assembled during late Upper Cretaceous-Middle Eocene times, when syn-tectonic sedimentary-olistostromic formations of Paleogene age were deposited above the northern ophiolite belt and the continental margin sections (Iturralde-Vinent., 1998).

Image source: García Delgado et al. (1998), in García-Casco et al., 2006, High pressure metamorphism of ophiolites in Cuba. Geologica Acta 4, 63-88.

Field aspect of serpentinite mélange with HP blocks south of Santa Clara and microscopic image of amphibole-eclogite block. Image source: A. García-Casco, unpublished.

Age determinations for the eclogite sample LV36A yielded 103.4±1.4 (40Ar/39Ar plateau age of amphibole), 115.0±1.1 (40Ar/39Ar plateau age of phengite; 123.1±1.0 to 117.1±0.9 intragrain laserprobe fusion ages) and 118.2±0.6 Ma (Rb/Sr isochron for phengite-omphacitewhole-rock; Schneider, 2000; García-Casco et al., 2002).

These data indicate that the minimum age of eclogite facies metamorphism is pre-118 Ma (Aptian or older), while final uplift and cooling dates to Aptian-Albian times (118-103 Ma). Thus, it is concluded that block LV36A formed in a subduction system of pre-Aptian age and that it was incorporated into the mélange and exhumed during the Aptian-Albian. The tectonic nature of the mélange-forming event is uncertain. However, the near-isothermal decompression sections of the retrograde part of the P-T paths followed by the HP block offer some insights into this problem. The decompression-dominated retrograde paths are similar to that termed Alpine type (Ernst, 1988), which is normally interpreted as the result of rapid exhumation in a relatively hot geothermal gradients imposed by tectonic unroofing after arrest of subduction. Though arrest of subduction is generally thought to be caused by collision of the subduction-forearc system with a buoyant down-going continental, oceanic, or arc lithosphere (Ernst, 1988; Ring et al., 1999; Wakabayashi, 2004), other collision tectonic processes, such as reversals of subduction polarity, have similar consequences, as discussed below. In either case, however, the retrograde paths of exotic blocks within the northern ophiolite belt in central Cuba are consistent with collision tectonics accompanying termination of subduction during the mid-Cretaceous.

Images source: García-Casco et al., 2002. Oscillatory zoning in eclogitic garnet and amphibole, Northern Serpentinite Melange, Cuba: a record of tectonic instability during subduction? Journal of Metamorphic Geology 20, 581–598.

(To the left petrologic model explaining formation of oscillatory zoning in garnet in response to subtle recurrent changes in P-T and tectonic interpretation of the P-T-t path fo sample DG6521B, from Holguín)