Y. Rojas-Agramonte

Metamorphic evolution of subducted hot oceanic crust (La Corea Mélange, Cuba)

Thermobarometric estimates and predictions of theoretical and experimental isochemical P-T phase diagrams for epidote±garnet amphibolite blocks from the serpentinite mélange of La Corea (eastern Cuba) indicate partial melting of subducted oceanic lithosphere occurred at peak metamorphic conditions of ca. 700 °C and 14 to 15 kbar. These anomalously high geothermal conditions suggest onset of subduction of young oceanic lithosphere of the Proto-Caribbean. The amphibolites have basaltic composition and MORB affinity. Partial melting produced tonalitic-trondhjemitic-granitic melts that crystallized at depth associated with the amphibolites. Calculated retrograde conditions for the amphibolites (450 °C and 8-10 kbar) indicate counterclockwise P-T paths during exhumation in the subduction channel, in agreement with published predictions on thermo-mechanical modeling of onset of subduction of young lithosphere. These findings have important consequences for the plate tectonic configuration of the Caribbean realm since they corroborate the existence of fragments of early subducted young oceanic lithosphere in the eastern Cuba mélanges that indicate subduction of an oceanic ridge during mid-Cretaceous times.

Timing and Evolution of Cretaceous Island Arc Magmatism in Central Cuba: Implications for the History of Arc Systems in the Northwestern Caribbean

SHRIMP and conventional zircon dating place temporal constraints on the evolution of the Cretaceous Volcanic Arc system in central Cuba. The arc has a consistent stratigraphy across strike, with the oldest and deepest rocks in the south (in tectonic contact with the ∼5–10-km-wide Mabujina Amphibolite Complex [MAC]) and younger rocks in the north. The MAC is thought to represent the deepest exposed section of the Cretaceous Volcanic Arc and its oceanic basement in Cuba. We undertook a single zircon geochronological study of five gneisses and two amphibolites from the MAC and seven rocks from the Manicaragua Batholith, which intrudes both the MAC and the Cretaceous Volcanic Arc. A SHRIMP zircon age of Ma for a trondhjemitic orthogneiss (MAC) from the Jicaya River dates the oldest phase of granitoid magmatism in this area and the entire Caribbean (Antillean) region. A tonalitic gneiss collected near the previous sample yielded an age of Ma, and a further tonalitic gneiss had an age of Ma, with one inherited zircon at Ma. Two trondhjemitic orthogneisses from the central part of the MAC yielded ages of and Ma, whereas two amphibolites from the eastern part of the complex provided similar ages of ca. 93 Ma and zircon inheritance at 315, 471, 903, and 1059 Ma. Two weakly foliated Manicaragua granitoids from the eastern part of the massif provided ages of and Ma, whereas five unfoliated granitoid samples from the central and eastern part of the massif yielded ages of , , , , and Ma. Our age data support the view that the Mabujina Protholiths are exotic and formed somewhere NNW along strike of the nonmetamorphosed Cuban arc since pre–Middle Hauterivian time (before ∼133 Ma). The MAC became part of the Cuban Volcanic Arc during the Turonian (ca. 90–93 Ma), when it was intruded by plutonic rocks of the Manicaragua Batholith (Turonian-Campanian; ca. 89–83 Ma). The geology and geochronology of central Cuba do not support the idea of a polarity reversal event at any stage of the Cretaceous Arc–building process. Because most of our dated samples come from the narrow Mabujina Belt, the polarity reversal model would imply that the axis of a newly developing arc (with opposite polarity) would spatially coincide with the older arc, which appears unlikely. Inherited Precambrian and Palaeozoic zircons in the MAC granitic rocks (similar to inherited zircon populations in the Guerrero terrane from central-western Mexico) suggest a Neocomian proximal setting close to a cratonic area (probably SW Mexico/Maya Block) for the protolith of the MAC relative to the synchronous Primitive Island Arc of central Cuba.

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.

Detrital zircon geochronology of Jurassic sandstones of western Cuba (San Cayetano Formation): Implications for the Jurassic paleogeography of the NW Proto-Caribbean

Clastic sediments of the early (?) to late Jurassic (Oxfordian) San Cayetano Formation of western Cuba are interpreted to reflect syn-rift sedimentation coeval with the breakup of Pangaea. This sedimentary unit is the oldest known in the Guaniguanico Mountains and Cuba. U-Pb SHRIMP dating of 19 detrital zircon grains from two samples of San Cayetano micaceous sandstone provided concordant ages ranging from ∼398 to 2479 Ma. The oldest zircon population is of Paleoproterozoic age (∼2479 − 1735 Ma), but most zircons have early Mesoproterozoic and Grenvillian ages (∼1556 − 985 Ma), whereas still younger ages are Pan-African (561 Ma), Ordovician (451 Ma) and early Devonian (∼398 Ma). We discuss the possible origin of these zircons and conclude that the most likely source terrain(s) are Precambrian and early Paleozoic massifs in northern South America (Colombia and/or Venezuela) and the Yucatán Peninsula in Mexico. This is compatible with paleogeographic reconstructions of the Caribbean that imply that sediments of the San Cayetano Formation were still part of the disintegrating supercontinent Pangea in pre mid-Oxfordian time.

ZIRCON AGES, Sr-Nd-Hf ISOTOPIC COMPOSITIONS, AND GEOCHEMISTRY OF GRANITOIDS ASSOCIATED WITH THE NORTHERN OPHIOLITE MELANGE OF CENTRAL CUBA: TECTONIC IMPLICATION FOR LATE CRETACEOUS MAGMATISM IN THE NORTHWESTERN CARIBBEAN

The geology of Cuba is representative of the orogenic belt fringing the northwesternmost margin of the Caribbean plate. It is characterized by a tectonic collage made up of a continental margin, volcanic arc, and ophiolitic and subduction complexes formed as a result of collision between the leading edge of the Caribbean plate and the Caribeana terrane in the latest Cretaceous to early Tertiary and by oblique convergence with the continental margin of the North American plate during Tertiary times. The northern ophiolite belt of central Cuba consists of a mélange containing blocks of eclogite, garnet-amphibolite, amphibolite, blueschist, greenschist, quartzite, metapelite, antigoritite and various types of intrusive rocks that occur as blocks or intrusive gabbro and diabase of the ophiolitic sequence. We present the first combined SHRIMP zircon U-Pb ages, Sr-Nd-Hf isotopic compositions as well as major and trace element data for nine arc-related granitoid rocks from the northern ophiolite mélange of central Cuba. A trondhjemite from the Cerro el Chivo area south of Santa Clara, provided a concordant zircon age of ∼86 Ma, whereas a granite and a tonalite from the Las Bocas body, north of Placetas, yielded ages of ∼75 Ma. Two peraluminous trondhjemitic samples taken from the Tres Guanos area S of Perea yielded zircon crystallization ages of ∼72 and ∼74 Ma, rare Cambrian (∼536 Ma) and Permian (∼268 Ma) inherited zircons were found in these samples. Hf isotope ratios were measured in five of the dated zircon grains from the Tres Guanos samples. The three youngest zircons, with ages of ∼72 and ∼74 Ma, show derivation from a depleted source region, as can be expected for arc granitoids, as well as the oldest xenocryst (∼536 Ma) which is less depleted but still from a juvenile Pan-African source. A Permian xenocryst (∼268 Ma) has a negative εHf(T) value (−2.35), implying that the zircon is derived from a continental source. The initial Nd isotopic composition εNd(t) of four of the dated granitoids is almost identical at 7.3 to 7.7 and implies a depleted source, whereas one of the Tres Guanos trondhjemite samples containing an inherited Cambrian zircon has a lower εNd(t) of 4.9, possibly reflecting input from an older crustal component. The initial Sr isotopic compositions of all five analyzed samples vary between 0.7031 and 0.7039 which are typical for I-type granitoids. The chemistry of these rocks is compatible with arc-related granitoids typical of a subduction setting. The zircon ages of this study constrain currently discussed geotectonic models and indicate that emplacement of the ophiolite mélange must be younger than 71 Ma. Based on current geodynamic models for the Caribbean, our data suggest that the oceanic crust in the northern ophiolite belt is of supra-subduction origin (probably fore-arc) related to a volcanic arc domain that formed during Late Cretaceous time. Apart from the granitoid sample from the Cerro el Chivo that was probably tectonically incorporated into the mélange, the remaining samples can be related to a pre-collision/collision calc-alkaline subduction-related environment.

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)

The 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.

Petrogenesis and 40Ar/39Ar dating of proto-forearc crust in the Early Cretaceous Caribbean arc: The La Tinta mélange (eastern Cuba) and its easterly correlation in Hispaniola

ABSTRACT The La Tinta mélange is a small but singular ultramafic mélange sheet that crops out in eastern Cuba. It is composed of dolerite-derived amphibolite blocks embedded in a serpentinite matrix. The amphibolite blocks have mid-ocean ridge basalt (MORB)-like composition showing little if any imprint of subduction zone component, similar to most forearc and MOR basalts worldwide. Relict Cr-spinel and olivine mineral chemistry of the serpentinized ultramafic matrix suggest a forearc position for these rocks. These characteristics, together with a hornblende 40Ar/39Ar age of 123.2 ± 2.2 Ma from one of the amphibolite blocks, suggest that the protoliths of the amphibolite blocks correspond to forearc basalt (FAB)-related rocks that formed during the earlier stage of subduction initiation of the Early Cretaceous Caribbean arc. We propose that the La Tinta amphibolites correspond to fragments of sills and dikes of hypoabyssal rocks formed in the earlier stages of a subduction initiation scenario in the Pacific realm (ca. 136 Ma). The forearc dolerite-derived amphibolites formed by partial melting of upwelling fertile asthenosphere at the beginning of subduction of the Proto-Caribbean (Atlantic) slab, with no interaction with slab-derived fluids/melts. This magmatic episode probably correlates with Early Cretaceous basic rocks described in Hispaniola (Gaspar Hernandez serpentinized peridotite-tectonite). The dikes and sills cooled and metamorphosed due to hydration at low pressure (ca. 3.8 kbar) and medium to high temperature (up to 720ºC) and reached ca. 500ºC at ca. 123 Ma. At this cooling stage, serpentinite formed after hydration of the ultramafic upper mantle. This process might have been favoured by faulting during extension of the forearc, indicating an early stage of dike and sill fragmentation and serpentinite mélanges formation; however, full development of the mélange likely took place during tectonic emplacement (obduction) onto the thrust belt of eastern Cuba during the latest Cretaceous.

The geology of Cuba: A brief overview and synthesis

Cuba is the largest island in the Greater Antilles, and its geology records three important episodes: (1) the Jurassic breakup of North and South America (Pangea) and associated passive margin and oceanic sedimentary and magmatic evolution; (2) the sedimentary, magmatic, and metamorphic evolution of an intra-oceanic Cretaceous-Paleogene ophiolite-arc complex; and (3) the Paleogene “soft collision” and transfer of the NW Caribbean plate (and Cuba) to the North American plate. Thick sequences of JurassicCretaceous strata (conglomerates, sandstones, limestones, dolostones, shales) and interlayered basaltic rocks characterize passive margin sequences preserved in the Guaniguanico terrane (western Cuba, related to the Mayan passive margin and the Gulf of Mexico) and the Bahamas Platform borderlands (north of Cuba). Passive margin deposition ceased in latest Cretaceous time, when increasing relief of accreted (overriding) oceanic arc and ophiolite complexes shed coarse sediments (olistostrome and flysch), followed by carbonate deposition. Fragments of the intervening oceanic lithosphere (Proto-Caribbean, connected to the Central Atlantic) and foreand back-arc oceanic lithosphere (Caribbean, of Pacific origin) occur as tectonic fragments detached from the ophiolitic units, including serpentinized harzburgites and dunites, banded and isotropic gabbros, basalts (tholeiitic and fore-arc basalts, locally with boninites) and Late Jurassic (Tithonian) through Late Cretaceous (Coniacian and younger) oceanic sediments. Arc activity in the Cuban segment of the Greater Antilles produced sedimentary, volcanic, and plutonic rocks during Cretaceous times (ca. 135–70 Ma). A new arc developed in eastern Cuba during Paleocene–middle Eocene times. Cuban arc sequences include island-arc tholeiitic, calcalkaline, and alkaline bimodal suites of volcanic and plutonic rocks. Remnants of ProtoCaribbean oceanic lithosphere occur as exhumed mélangebearing eclogite-, blueschist-, and garnet-amphibolite-facies tectonic blocks (oldest age ca. 120 Ma) within a serpentinite matrix intercalated with, or at the base of, the overthrusted ophiolitic bodies. Cuban Cretaceous arc magmatic activity ended due The geology of Cuba: A brief overview and synthesis to the subduction of Proto-Caribbean passive margin sequences of the Caribeana terrane, an offshore protuberance of Yucatan. This event formed strongly deformed high-pressure metasedimentary and metaigneous rocks at ca. 70 Ma, when the Caribbean plate began to collide with North America. The collision, which included overriding of the ophiolitic and arc units over both subducted and unsubducted passive margin sequences, also produced synorogenic basins and filled them, a process that continued until ca. 40 Ma. This foldbelt was succeeded by local uplift and subsidence to form late Eocene–Recent unconformable post-orogenic continental basins. INTRODUCTION AND GEOLOGIC SETTING Cuba has had a very interesting geologic evolution. The island is geographically very near the United States, but for political reasons, U.S. geoscientists have not been able to study it much. In this overview, we highlight the geology of Cuba. Useful publications on Cuban geology produced during the past quarter century can be found in Ceballos Izquierdo and Iturralde-Vinent (2016). We hope that the improving political situation will increase mutually beneficial interactions in the future. A few relevant geographic and demographic facts about Cuba are listed in Table 1. Cuba is the largest island in the Greater Antilles and has been part of the North American plate (NOAM) since late Eocene time. It is separated from other Greater Antilles islands by the North