Ophiolite-Related Ultramafic Rocks (Serpentinites) in the Caribbean Region : a Review of their Occurrence, Composition, Origin, Emplacement and Ni-Laterite Soil Formation

Ultramafic rocks, mainly serpentinized peridotites of mantle origin, are mostly associated with the ophiolites of Mesozoic age that occur in belts along three of the margins of the Caribbean plate. The most extensive exposures are in Cuba. The ultramafic-mafic association (ophiolites) were formed and emplaced in several different tectonic environments. Mineralogical studies of the ultramafic rocks and the chemistry of the associated mafic rocks indicate that most of the ultramafic-mafic associations in both the northern and southern margins of the plate were formed in arc-related environments. There is little mantle peridotite exposed in the ophiolitic associations of the west coast of Central America, in the south Caribbean in Curacao and in the Andean belts in Colombia. In these occurrences the chemistry and age of the mafic rocks indicates that this association is mainly part of the 89 Ma Caribbean plateau province. The age of the mantle peridotites and associated ophiolites is probably mainly late Jurassic or Early Cretaceous. Emplacement of the ophiolites possibly began in the Early Cretaceous in Hispaniola and Puerto Rico, but most emplacement took place in the Late Cretaceous to Eocene (e.g. Cuba). Along the northern South America plate margin, in the Caribbean mountain belt, emplacement was by major thrusting and probably was not completed until the Oligocene or even the early Miocene. Caribbean mantle peridotites, before serpentinization, were mainly harzburgites, but dunites and lherzolites are also present. In detail, the mineralogical and chemical composition varies even within one ultramafic body, reflecting melting processes and peridotite/melt interaction in the upper mantle. At least for the northern Caribbean, uplift (postemplacement tectonics) exposed the ultramafic massifs as a land surface to effective laterization in the beginning of the Miocene. Tectonic factors, determining the uplift, exposing the peridotites to weathering varied. In the northern Caribbean, in Guatemala, Jamaica, and Hispaniola, uplift occurred as a result of transpresional movement along pre-existing major faults. In Cuba, uplift occurred on a regional scale, determined by isostatic adjustment. In the south Caribbean, uplift of the Cordillera de la Costa and Serrania del Interior exposing the peridotites, also appears to be related to strike-slip movement along the El Pilar fault system. In the Caribbean, Ni-laterite deposits are currently being mined in the central Dominican Republic, eastern Cuba, northern Venezuela and northwest Colombia. Although apparently formed over ultramafic rocks of similar composition and under similar climatic conditions, the composition of the lateritic soils varies. Factors that probably determined these differences in laterite composition are geomorphology, topography, drainage and tectonics. According to the mineralogy of principal ore-bearing phases, Dominican Ni-laterite deposits are classified as the hydrous silicate-type. The main Ni-bearing minerals are hydrated Mg-Ni silicates (serpentine and "garnierite") occurring deeper in the profile (saprolite horizon). In contrast, in the deposits of eastern Cuba, the Ni and Co occurs mainly in the limonite zone composed of Fe hydroxides and oxides as the dominant mineralogy in the upper part of the profile, and are classified as the oxide-type

The metallogenic evolution of the Greater Antilles

The Greater Antilles host some of the world’s most important deposits of bauxite and lateritic nickel as well as significant resources of gold and silver, copper, zinc, manganese, cobalt and chromium. Beginning in Jurassic time, sedimentary exhalative base metal deposits accumulated in marine sedimentary rift basins as North and South America drifted apart. With the onset of intraoceanic subduction during the Early Cretaceous, a primitive (tholeiitic) island arc formed above a southwesterly-dipping subduction zone. Podiform chromite deposits formed in the mantle portion of the supra-subduction zone, directly above subducted Proto-Caribbean oceanic lithosphere. Within the nascent island arc, bimodal-mafic volcanogenic massive sulfide deposits formed in a fore-arc setting; mafic volcanogenic massive sulfide deposits formed later in mature back-arc basins. The Pueblo Viejo gold district, with five million ounces in production and twenty million ounces in mineable reserves, formed at 108-112Ma, in an apical rift or back-arc setting. By Late Cretaceous time, calc-alkaline volcanism was well established along the entire length of the Greater Antilles. Volcanogenic massive sulfide deposits including shallow submarine deposits characteristic of the primitive island arc gave way to porphyry copper and epithermal precious metal deposits typical of the mature island arc. Oblique collision of the Greater Antilles with North America began in the Late Cretaceous in Cuba and migrated eastward. Orogenic gold and tungsten deposits that formed during the collision event are preserved in ophiolites and in metamorphic core complexes. Since the Eocene, regional tectonism has been dominated by strike-slip motion as the North American continent moved westward relative to the Caribbean Plate. Large nickel-cobalt laterite deposits were formed when serpentinites were exposed to weathering and erosion during the mid-Tertiary. Bauxite deposits were derived from the weathering of volcanic ash within a carbonate platform of Eocene to Miocene ag

Serpentinites and serpentinites within a fossil subduction channel : La Corea mélange, eastern Cuba

A variety of metaultramafic (serpentinite) rocks in La Corea mélange, Sierra de Cristal, eastern Cuba, show differences in chemical, textural and mineralogical characteristics demonstrating a variety of protoliths. The mélange originated during the Cretaceous as part of the subduction channel associated with the Caribbean island arc. This mélange contains high pressure blocks in a serpentinite matrix and occurs at the base of the large tabular Mayarí-Cristal ophiolite. Two principal groups of serpentinites have been identified in the mélange: a) antigorite serpentinite, mainly composed of antigorite and b) antigorite-lizardite serpentinite, composed of mixtures of antigorite and lizardite and bearing distinctive porphyroblasts of diopsidic clinopyroxene. Antigorite serpentinites are closely related to tectonic blocks of amphibolite (representing subducted MORB) and constitute deep fragments of the serpentinitic subduction channel formed during hydration of the mantle wedge. The composition of the antigorite-lizardite serpentinites and the presence of clinopyroxene porphyroblasts in this type of rock suggest that abyssal lherzolite protoliths transformed into serpentinite before and during incorporation (as tectonic blocks) in the shallow part of the subduction channel. Although the studied rocks have different origin, mineralogical compositions and textures, they display similar PGE compositions, suggesting that these elements experienced no significant redistribution during metamorphism. Both types of serpentinites were exposed together in the La Corea mélange during the Late Cretaceous, during obduction of the overriding Mayarí-Baracoa ophiolitic belt that led to exhumation of the subduction channel (mélange)

Chromite and platinum group elements mineralization in the Santa Elena Ultramafic Nappe (Costa Rica): geodynamic implications

Chromitites associated with strongly altered peridotite from six distinct localities in the Santa Elena ultramafic nappe (Costa Rica) have been investigated for the first time. Santa Elena chromitites commonly display a compositional variation from extremely chromiferous (Cr/(Cr+Al)=0.81) to intermediate and aluminous (Cr/(Cr+Al)=0.54). This composition varies along a continuous trend, corresponding to calculated parental liquids which may have been derived from the differentiation of a single batch of boninitic magma with Cr-rich and (Al, Ti)-poor initial composition. Fractional precipitation of chromite probably occurred during differentiation of the boninitic melt and progressive metasomatic reaction with mantle peridotite. The distribution of platinum group elements (PGE) displays the high (Os+Ir+Ru)/(Rh+Pt+Pd) ratio typical of ophiolitic chromitites and, consistently, the platinum group minerals (PGM) encountered are mainly Ru-Os-Ir sulfides and arsenides. Textural relations of most of the platinum group elements suggest crystallization at magmatic temperatures, possibly under relatively high sulfur fugacity as indicated by the apparent lack of primary Os-Ir-Ru alloys. The chemical and mineralogical characteristics of chromitites from the Santa Elena ultramafic nappe have a strong affinity to podiform chromitites in the mantle section of supra-subduction-zone ophiolites. Calculated parental melts of the chromitites are consistent with the differentiation of arc-related magmas, and do not support the oceanic spreading center geodynamic setting previously proposed by some authors

Petrogenesis of fertile mantle peridotites from the Monte del Estado massif (Southwest Puerto Rico): a preserved section of Proto-Caribbean lithospheric mantle?

The Monte del Estado massif is the largest and northernmost serpentinized peridotite belt in southwest Puerto Rico. It is mainly composed of spinel lherzolite and minor harzburgite with variable clinopyroxene modal abundances. Mineral and whole rock major and trace element compositions of peridotites coincide with those of fertile abyssal mantle rocks from mid ocean ridges. Peridotites lost 2-14 wt% of relative MgO and variable amounts of CaO by serpentinization and seafloor weathering. HREE contents in whole rock indicate that the Monte del Estado peridotites are residues after low to moderate degrees (2-15%) of fractional partial melting in the spinel stability field. However, very low LREE/HREE and MREE/HREE in clinopyroxene cannot be explained by melting models of a spinel lherzolite source and support that the Monte del Estado peridotites experienced initial low fractional melting degrees (~ 4%) in the garnet stability field. The relative enrichment of LREE in whole rock is not due to alteration processes but probably reflects the capture of percolating fluid/melt fractions or the crystallization of sub-percent amounts of hydrous minerals (e.g., amphibole, phlogopite) along grain boundaries or as microinclusions in minerals. We propose that the Monte del Estado peridotite belt represents a section of ancient Proto-Caribbean (Atlantic) lithospheric mantle originated by seafloor spreading between North and South America in the Late Jurassic- Early Cretaceous. This portion of oceanic lithospheric mantle was subsequently trapped in the forearc region of the Greater Antilles paleo-island arc generated by the northward subduction of the Caribbean plate beneath the Proto-Caribbean ocean. Finally, the Monte del Estado peridotites belt was emplaced in the Early Cretaceous probably as result of the change in subduction polarity of the Greater Antilles paleo-island arc without having been significantly modified by subduction processe

Cadomian metabasites of the Eastern Pyrenees revisited

This study presents a new geochemical, petrological, and geochronological U–Pb dataset from Ediacaran metabasites of the Canigó and Cap de Creus massifs, Eastern Pyrenees. The rocks are composed of calcic amphibole + plagioclase + chlorite + epidote ± quartz plus titanite + apatite + ilmenite ± biotite ± rutile as accessory phases and show relict igneous textures. Peak pressure-temperature determinations share common conditions, ranging 452–482ºC and 5.2–7.7kbar. These intermediate P-T conditions suggest Barrovian-type metamorphism, most likely related to a collisional setting. The metabasites correspond to evolved basaltic rocks (Mg#<0.55) with moderate TiO2 content (up to 2.08wt.%) and relatively low Cr (43–416ppm). The rocks are moderately enriched in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) (average (La/Lu)n of 2.7) and the N-MORB normalized multi-element patterns show negative slopes, with prominent negative Nb anomalies ((Nb/La)NMORB=0.33–0.78). These variations are akin to island arc tholeiites generated in back-arc basins and to other metabasites described in the Eastern Pyrenees with a putative Ediacaran age, and they differ from the Ordovician tholeiitic metabasites from the Canigó massif, which derived from a contaminated E-MORB source. The positive ƐNd(T) values (0.82–3.05) of the studied metabasites preclude a notable contribution from an older continental crust. U-Pb dating (LA-ICP-MS) of one chlorite-rich schist sample in contact with the metabasites from the Canigó massif yielded a main peak at ca. 632Ma. We argue that the Cadomian metabasites from the Pyrenees formed during back-arc extension in the continental margin of Gondwana and were later affected by (probably early Variscan) medium-P metamorphism before the HT-LP metamorphism classically described in the Pyrenees

L\u27evolution historique de la privilege au premier saisissant et la conception francais de la egalite des creanciers

The Mayari-Baracoa Ophiolitic Belt (MBOB, eastern Cuba) is composed of two large, chromite-rich massifs: Mayari-Cristal and Moa-Baracoa. The chromitites and hosting dunites were firstly affected by a regional serpentinization event, a subsequent episode of hydrothermal alteration (chloritization mainly) and, finally, these already altered bodies were crosscut by thin calcite-dominated veins. Analysed serpentines from serpentinized chromitites and dunites present very similar isotopic compositions (delta(18)O= + 4.7 parts per thousand to + 6.3 parts per thousand and deltaD = - 67 parts per thousand to - 60 parts per thousand), suggesting that the serpentinization process took place at moderate temperatures, in an oceanic environment. Serpentine formation by interaction with ocean water is also supported by the isotopic composition of chlorite and calcite. These results suggest that the serpentinization, chloritization and fracture filling processes of the Mayari-Baracoa Ophiolite Belt took place in a subocean floor scenario and, thus, that the Mayari-Baracoa serpentines represent a good example of serpentine formed during interaction with seawater. The oceanic origin of the serpentines from serpentinized chromitites and dunites from the MBOB indicate that the serpentinization of the mantle sequence occurred pre-thrusting (pre-emplacement in age). (C) 2003 Elsevier Science B.V. All rights reserved

High-pressure greenschist to blueschist facies transition in the Maimón Formation (Dominican Republic) suggests mid-Cretaceous subduction of the Early Cretaceous Caribbean Arc

The Maimón Formation (Cordillera Central, Dominican Republic) is formed of metamorphosed bi-modal mafic-felsic volcanic rocks and sedimentary horizons of Early Cretaceous age deposited in the forearc of the nascent Caribbean island arc. Two structural-metamorphic zones depict an inverted metamorphic gradient: the Ozama shear zone, which records intense mylonitic and phyllonitic deformation and ubiquitous metamorphic recrystallization, tectonically overlies the much less deformed and variably recrystallized rocks of the El Altar zone. The presence of ferri-winchite and high-Si phengite, first reported in this paper, in the peak metamorphic assemblage of rocks of the Ozama shear zone (actinolite + phengite + chlorite + epidote + quartz + albite ± ferri-winchite ± stilpnomelane) point to subduction-related metamorphism. Pseudosection calculations and intersection of isopleths indicate peak metamorphic conditions of ~ 8.2 kbar at 380 °C. These figures are consistent with metamorphism in the greenschist/blueschist facies transition, burial depths of ~ 25-29 km and a thermal gradient of ~ 13-16 °C/km. Our new data dispute previous models pointing to metamorphism of Maimón rocks under a steep thermal gradient related to burial under a hot peridotite slice. Instead, we contextualize the metamorphism of the Maimón Formation in a subduction scenario in which a coherent slice of the (warm) Early Cretaceous forearc was engulfed due to intra-arc complexities and regional-scale-driven tectonic processes operating in the late Early Cretaceous. Integration of our findings with previous studies on metamorphic complexes in Hispaniola suggests that a major tectonic event affecting the whole arc system took place at c. 120-110 Ma

Cadomian metabasites of the Eastern Pyrenees revisited

This study presents a new geochemical, petrological, and geochronological U-Pb dataset from Ediacaran metabasites and associated rocks of the Canigó and Cap de Creus massifs, Eastern Pyrenees. Metabasites are composed of calcic amphibole + plagioclase + chlorite + epidote ± quartz plus titanite + apatite + ilmenite ± biotite ± rutile as accessory phases and show relict igneous textures. Peak pressure-temperature determinations share common conditions, ranging 452-482ºC and 5.2-7.7kbar, which suggest Barrovian-type metamorphism, most likely related to a collisional setting. The metabasites correspond to evolved basaltic rocks (Mg#<0.55) with moderate TiO2 content (up to 2.08wt.%) and relatively low Cr (43-416ppm). The rocks are moderately enriched in Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE) (average (La/Lu)n of 2.7) and the N-MORB normalized multi-element patterns show negative slopes, with prominent negative Nb anomalies ((Nb/La)NMORB=0.33–0.78). These variations are akin to island arc tholeiites generated in back-arc basins and to other metabasites described in the Eastern Pyrenees with a putative Ediacaran age, and they differ from the Ordovician tholeiitic metabasites from the Canigó massif, which derived from a contaminated E-MORB source. The positive ƐNd(T) values (0.82-3.05) of the studied metabasites preclude a notable contribution from an older continental crust. Detrital zircon U-Pb dating Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) of one chlorite-rich schist sample in contact with the metabasites from the Canigó massif yielded a main peak at ca. 632Ma and apparent maximum age of deposition at ca. 550Ma. We argue that the Cadomian metabasites from the Pyrenees formed during back-arc extension in the continental margin of Gondwana and were later affected by (probably early Variscan) medium-P metamorphism before the Low-Pressure High-Temperature (LP-HT) metamorphism classically described in the Pyrenees