Geology, age and tectonic evolution of the Sierra Maestra Mountains, southeastern Cuba

We summarize the available geological information on the Sierra Maestra Mountains in southeastern Cuba and report new zircon fission track and biotite Ar-Ar ages for this region. Two different and genetically unrelated volcanic arc sequences occur in the Sierra Maestra, one Cretaceous in age (pre-Maastrichtian) and restricted to a few outcrops on the southern coast, and the other Palaeogene in age, forming the main expression of the mountain range. These two sequences are overlain by middle to late Eocene siliciclastic, carbonatic and terrigenous rocks as well as by late Miocene to Quaternary deposits exposed on the southern flank of the mountain range. These rocks are britle deformed and contain extension gashes filled with calcite and karst material. The Palaeogene volcanic arc successions were intruded by calc-alkaline, low- to medium-K tonalites and trondhjemites during the final stages of subduction and subsequent collision of the Caribbean oceanic plate with the North American continental plate. U-Pb SHRIMP single zircon dating of five granitoid plutons yielded 206Pb/238U emplacement ages between 60.5 ± 2.2 and 48.3 ± 0.5 Ma. These granitoids were emplaced at pressures ranging from 1.8 to 3.0 kbar, corresponding to depths of ca. 4.5-8 km. 40Ar/39Ar dating of two biotite concentrates yielded ages of 50 ± 2 and 54 ± 4 Ma, indicating cooling through ca. 300 ºC. Zircon and apatite fission track ages range from 32 ± 3 to 46 ± 4 Ma and 31 ± 10 to 44 ± 13 Ma, respectively, and date cooling through 250 ± 50 ºC and 110 ± 20 ºC. The granitoids are the result of subduction-related magmatism and have geochemical characteristics similar to those of magmas from intra-oceanic island-arcs such as the Izu Bonin-Mariana arc and the New Britain island arc. Major and trace element patterns suggest evolution of these rocks from a single magmatic source. Geochemical features characterize these rocks as typical subduction-related granitoids as found worldwide in intra-oceanic arcs, and they probably formed through fractional crystallization of mantlederived low- to medium-K basalts. Several distinct phases of deformation were recognized in the Sierra Maestra, labelled D1 to D6, which define the transition from collision of the Palaeogene island arc to the formation of the Oriente Transform Wrench Corridor south of Cuba and later movement of the Caribbean plate against the North American plate. The first phase (D1) is related to the intrusion of a set of extensive subparallel, N-trending subvertical basalt-andesite dykes, probably during the early to middle Eocene. Between the late-middle Eocene and early Oligocene (D2), rocks of the Sierra Maestra were deformed by approximately east-west trending folds and north-vergent thrust faults. This deformation (D2) was linked to a shift in the stress regime of the Caribbean plate from mainly NNE-SSW to E-W. This shift in plate motion caused the abandonment of the Nipe-Guacanayabo fault system in the early Oligocene and initiation of a deformation front to the south where the Oriente Transform Wrench corridor is now located. Compressive structures were overprinted by widespread extensional structures (D3), mainly faults with southward-directed normal displacement in the Oligocene to early Miocene. During this period the plate boundary jumped to the Oriente fault. This event was followed by transpressive and transtensive structures (D4-D6) due to further development of the sinistral E-trending Oriente Transform wrench corridor. These structures are consistent with oblique convergence in a wide zone of left-lateral shear along an E-W-oriented transform fault

Experimental evidence for the preservation of U-Pb isotope ratios in mantle-recycled crustal zircon grains

Zircon of crustal origin found in mantle-derived rocks is of great interest because of the information it may provide about crust recycling and mantle dynamics. Consideration of this requires understanding of how mantle temperatures, notably higher than zircon crystallization temperatures, affected the recycled zircon grains, particularly their isotopic clocks. Since Pb2+ diffuses faster than U4+ and Th+4, it is generally believed that recycled zircon grains lose all radiogenic Pb after a few million years, thus limiting the time range over which they can be detected. Nonetheless, this might not be the case for zircon included in mantle minerals with low Pb2+ diffusivity and partitioning such as olivine and orthopyroxene because these may act as zircon sealants. Annealing experiments with natural zircon embedded in cristobalite (an effective zircon sealant) show that zircon grains do not lose Pb to their surroundings, although they may lose some Pb to molten inclusions. Diffusion tends to homogenize the Pb concentration in each grain changing the U-Pb and Th-Pb isotope ratios proportionally to the initial 206Pb, 207Pb and 208Pb concentration gradients (no gradient-no change) but in most cases the original age is still recognizable. It seems, therefore, that recycled crustal zircon grains can be detected, and even accurately dated, no matter how long they have dwelled in the mantle.This paper has been financed by the Spanish Grants CGL2013-40785-P and CGL2017-84469-P

Minerales 'exóticos' en cromititas ofiolíticas. Implicaciones para la geodinámica mantélica

Los depósitos ofiolíticos de cromita constituyen un rasgo característico de la secuencia mantélica de las ofiolitas (González-Jiménez et al., 2014 y referencias en éste). Los cuerpos de cromititas se encuentran en dunitas y harzburgitas distribuyéndose a lo largo de una zona de espesor variable, entre 1 y 2 km, debajo de los niveles de gabros bandeados de la corteza inferior oceánica. El origen de cuerpos monominerálicos de cromita en el manto, especialmente el mecanismo de concentración de cromita y el ambiente tectónico de formación, continúa siendo un tema sujeto a debate (e.g., Proenza et al., 1999; González-Jiménez et al., 2014). A tal efecto, se han propuesto hipótesis basadas en: i) cristalización cotéctica de cromita+olivino y su posterior separación mecánica; ii) procesos de mezcla o contaminación de magmas; iii) asimilación de piroxenitas y gabros; iv) aumento del grado de polimerización del fundido debido a la pérdida de agua; v) cambios en la fugacidad de oxígeno. Todas estas hipótesis asumen procesos a baja presión en el manto (<20 km profundidad)

Zircon reconnaissance dating of Proterozoic gneisses along the Kunene River of northwestern Namibia

The northern margin of the Epupa Metamorphic Complex (EMC) along the Kunene River in NW Namibia is one of the geologically least known terranes in Africa because of its remoteness and difficult accessibility. We report field relationships and reconnaissance zircon ages for granitoid gneisses from a 120. km foot-traverse along the Kunene River between the Ruacana Falls in the east and Marienfluss in the west. Most rocks are late Palaeoproterozoic in age and correlate well with similar rocks of the EMC farther south in Kaokoland (1757-1835. Ma, one sample 1861. Ma) and with granitoid rocks in the Kamanjab Inlier, some 400. km SE of the Kunene River (1801-1836. Ma). All these rocks constitute a large magmatic province on the southwestern margin of the Congo Craton, whose protoliths are possibly related to arc magmatism during the Africa-wide so-called Eburnian event (ca. 2000. ±. 200. Ma). However, there are also Mesoproterozoic granitoids, 1520-1530. Ma in age, whose tectonic significance remains uncertain but which seem to document a thermal event also seen in high-grade metamorphism and isotopic resetting in this part of SW Africa

Review of Geochronologic and Geochemical Data of the Greater Antilles Volcanic Arc and Implications for the Evolution of Oceanic Arcs

Abstract The Greater Antilles islands of Cuba, Hispaniola, Puerto Rico and Jamaica plus the Virgin Islands host fragments of the fossil convergent margin that records Cretaceous subduction (operated for about 90 m.y.) of the American plates beneath the Caribbean plate and ensuing arc‐continent collision in Late Cretaceous‐Eocene time. The “soft” collision between the Greater Antilles Arc (GAA) and the Bahamas platform (and the margin of the Maya Block in western Cuba) preserved much of the convergent margin. This fossil geosystem represents an excellent natural laboratory for studying the formation and evolution of an intra‐oceanic convergent margin. We compiled geochronologic (664 ages) and geochemical data (more than 1,500 analyses) for GAA igneous and metamorphic rocks. The data was classified with a simple fourfold subdivision: fore‐arc mélange, fore‐arc ophiolite, magmatic arc, and retro‐arc to inspect the evolution of GAA through its entire lifespan. The onset of subduction recorded by fore‐arc units, together with the oldest magmatic arc sequence shows that the GAA started in Early Cretaceous time and ceased in Paleogene time. The arc was locally affected (retro‐arc region in Hispaniola) by the Caribbean Large Igneous Province (CLIP) in Early Cretaceous and strongly in Late Cretaceous time. Despite multiple biases in the database presented here, this work is intended to help overcome some of the obstacles and motivate systematic study of the GAA. Our results encourage exploration of offshore regions, especially in the east where the forearc is submerged. Offshore explorations are also encouraged in the south, to investigate relations with the CLIP

Early Palaeozoic Deep Subduction of Continental Crust in the Kyrgyz North Tianshan: Evidence from Field Relationships and Geochronology

International audienc

From intra-oceanic subduction to arc accretion and arc-continent collision: Insights from the structural evolution of the Río San Juan metamorphic complex, northern Hispaniola

The Río San Juan metamorphic complex exposes a segment of a high-pressure subduction-accretionary complex built during Caribbean island arc-North America continental margin convergence. It is composed of accreted arc- and oceanic-derived metaigneous rocks, serpentinized peridotites and minor metasediments forming a structural pile. Combined detailed mapping, structural and metamorphic analysis, and geochronology show that the deformation can be divided into five main events (D1-D5). An early subduction-related D1 deformation and M1 metamorphism produced greenschist (mafic rocks of the Gaspar Hernández peridotite-tectonite), blueschist and eclogite (metamafic blocks in the Jagua Clara mélange), high-P epidote-amphibolite and eclogite (Cuaba unit), and lower blueschist and greenschist-facies conditions (Morrito unit). This was followed by M2 decompression and cooling in the blueschist, greenschist and low-P amphibolite-facies conditions. The shape of the retrograde P-T path, the age of the exhumation-related D2 structures, and the tectonic significance of D2 deformation are different in each structural unit. Published U-Pb and 40Ar/39Ar plateau ages and T-t/P-t estimations reveal diachronic Turonian-Coniacian to Maastrichtian retrograde M2 metamorphism in the different structural units of the complex, during a consistent D2 top-to-the-NE/ENE tectonic transport. Regionally, a similar top-to-the-ENE tectonic transport also took place in the metasedimentary nappes of the Samaná complex during the Eocene to earliest Miocene. This kinematic compatibility indicates a general northeastward progradation of deformation in the northern Caribbean convergent margin, as the successive tectonic incorporation of arc, oceanic and continental-derived terrains to the developing Caribbean subduction-accretionary complex took place. D3-D5 deformations are discontinuous and much less penetrative, recording the evolution from ductile to brittle conditions of deformation in the complex. The D3 event substantially modified the nappe-stack and produced open folds with amplitudes up to kilometer-scale. The Late Paleocene-Eocene D4 structures are ductile to ductile-brittle thrusts and inverse shear bands. D5 is a Tertiary, entirely brittle deformation that had considerable influence in the geometry of the whole complex. From the Miocene to the Present, it has been cut and laterally displaced by a D5 sinistral strike-slip fault system associated with the Septentrional fault zone. © 2012 Elsevier Ltd.Funding by the Spanish Ministerio Ciencia e Innovación projects CGL2009-08674/BTE and CGL2012-33669/BTE is gratefully acknowledged. The research is a contribution to IGCP-546 “Subduction zones of the Caribbean”.Peer Reviewe

From intra-oceanic subduction to arc accretion and arc-continent collision: Insights from the structural evolution of the Río San Juan metamorphic complex, northern Hispaniola

The Río San Juan metamorphic complex exposes a segment of a high-pressure subduction-accretionary complex built during Caribbean island arc-North America continental margin convergence. It is composed of accreted arc- and oceanic-derived metaigneous rocks, serpentinized peridotites and minor metasediments forming a structural pile. Combined detailed mapping, structural and metamorphic analysis, and geochronology show that the deformation can be divided into five main events (D1-D5). An early subduction-related D1 deformation and M1 metamorphism produced greenschist (mafic rocks of the Gaspar Hernández peridotite-tectonite), blueschist and eclogite (metamafic blocks in the Jagua Clara mélange), high-P epidote-amphibolite and eclogite (Cuaba unit), and lower blueschist and greenschist-facies conditions (Morrito unit). This was followed by M2 decompression and cooling in the blueschist, greenschist and low-P amphibolite-facies conditions. The shape of the retrograde P-T path, the age of the exhumation-related D2 structures, and the tectonic significance of D2 deformation are different in each structural unit. Published U-Pb and 40Ar/39Ar plateau ages and T-t/P-t estimations reveal diachronic Turonian-Coniacian to Maastrichtian retrograde M2 metamorphism in the different structural units of the complex, during a consistent D2 top-to-the-NE/ENE tectonic transport. Regionally, a similar top-to-the-ENE tectonic transport also took place in the metasedimentary nappes of the Samaná complex during the Eocene to earliest Miocene. This kinematic compatibility indicates a general northeastward progradation of deformation in the northern Caribbean convergent margin, as the successive tectonic incorporation of arc, oceanic and continental-derived terrains to the developing Caribbean subduction-accretionary complex took place. D3-D5 deformations are discontinuous and much less penetrative, recording the evolution from ductile to brittle conditions of deformation in the complex. The D3 event substantially modified the nappe-stack and produced open folds with amplitudes up to kilometer-scale. The Late Paleocene-Eocene D4 structures are ductile to ductile-brittle thrusts and inverse shear bands. D5 is a Tertiary, entirely brittle deformation that had considerable influence in the geometry of the whole complex. From the Miocene to the Present, it has been cut and laterally displaced by a D5 sinistral strike-slip fault system associated with the Septentrional fault zone. © 2012 Elsevier Ltd.Funding by the Spanish Ministerio Ciencia e Innovación projects CGL2009-08674/BTE and CGL2012-33669/BTE is gratefully acknowledged. The research is a contribution to IGCP-546 “Subduction zones of the Caribbean”.Peer Reviewe

Did the Turonian–Coniacian plume pulse trigger subduction initiation in the Northern Caribbean? Constraints from 40Ar/39Ar dating of the Moa-Baracoa metamorphic sole (eastern Cuba),

International audienceThe Güira de Jauco metamorphic sole, below the Moa-Baracoa ophiolite (eastern Cuba), contains strongly deformed amphibolites formed at peak metamorphic conditions of 650–660°C, approximately 8.6 kbar (~30 km depth). The geochemistry, based on immobile elements of the amphibolites, suggests oceanic lithosphere protholiths with a variable subduction component in a supra-subduction zone environment. The geochemical similarity and tectonic relations among the amphibolites and the basic rocks from the overlying ophiolite suggest a similar origin and protholith. New hornblende 40Ar/39Ar cooling ages of 77–81 Ma obtained for the amphibolites agree with this hypothesis, and indicate formation and cooling/exhumation of the sole in Late Cretaceous times. The cooling ages, geochemical evidence for a back-arc setting of formation of the mafic protoliths, and regional geology of the region allow proposal of the inception of a new SW-dipping subduction zone in the back-arc region of the northern Caribbean arc during the Late Cretaceous (ca. 90–85 Ma). Subduction inception was almost synchronous with the main plume pulse of the Caribbean–Colombian Oceanic Plateau (92–88 Ma) and occurred around 15 million years before arc-continent collision (75 Ma–Eocene) at the northern leading edge of the Caribbean plate. This chronological framework suggests a plate reorganization process in the region triggered by the Caribbean–Colombian mantle plume

The imprint of subduction fluids on subducted MORB-derived melts (Sierra del Convento Melange, Cuba)

International audienceMajor and trace element signatures and Sr-Nd-Pb isotope data for muscovite (Ms)-bearing amphibolite blocks and associated muscovite-bearing trondhjemite and quartz-muscovite rocks from the Sierra del Convento melange (eastern Cuba) indicate that Proto-Caribbean oceanic crust underwent wet partial melting processes during Mesozoic subduction and after accretion to the upper plate. Trace element normalized patterns of Ms-bearing amphibolites are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE) and evidence variable trace element transfer from the Proto-Caribbean subducting slab to the mantle wedge. Ms-bearing trondhjemites show LREE enrichment and HREE depletion and have geochemical features similar to adakites, including SiO2>56 wt.%, high Na2O contents (5.5-9.0 wt.%) and high Sr/Y (16-644). We consider that the trondhjemites represent primary and natural melts formed by deep partial melting of the subducting slab which did not significantly react with the mantle wedge before intrusion in the subduction channel. The Ms-bearing trondhjemites show different geochemical and petrological signatures compared with the Ms-free tonalites-trondhjemites from Sierra del Convent, that are interpreted as primary slab melts. These differences support the idea that partial melting processes in the Sierra del Convento subduction channel were triggered by the infiltration of fluids derived from three distinct subducted sources: sediments, altered mid-ocean ridge basalts (MORB), and serpentinites. In this scenario, the pegmatitic quartz-muscovite rocks, which are highly enriched in LILE, probably represent the crystallization products of fluids derived by differentiation of the trondhjemitic melts