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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 fore-and 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 mélange-bearing 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.

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The 16 samples of Deep Sea Drilling Project (DSDP) Leg 89 basalts that we analyzed for whole rock major and trace elements and for mineralogic compositions are identical to some of the basalts recovered during Leg 61. Leg 89 samples are mostly olivine-plagioclase-clinopyroxene sparsely phyric basalts and exhibit a wide variety of textures. These basalts have lower TiO 2 at a given Mg/(Mg + Fe 2 +) × 100 than MO RB (midocean ridge basalt). We recognize three major chemical types of basalts in the Nauru Basin. We believe that different degrees of partial melting, modified by fractional crystallization and possibly by magma mixing at shallow depths, can explain the chemical differences among the three groups. This petrogenetic model is consistent with the observed downhole chemical-chronostratigraphic relations of the samples. New 87 Sr/ 86 Sr and U3 Nd/ 144 Nd analyses of basalt samples from DSDP Site 462 indicate that the Nauru Basin igneous complex is within the Sr-Nd isotopic range of ocean island basalt. Thus the Nauru Basin igneous complex resembles MORB in many aspects of its chemistry, morphology, and secondary alteration patterns (Larson, Schlanger, et al., 1981), but not in its isotopic characteristics. If it were not for the unambiguous evidence that the Nauru Basin complex was erupted off-ridge, the complex could easily be interpreted as normal oceanic layer 2. For this reason, we speculate that the Nauru Basin igneous complex was produced in an oceanic riftlike environment when multiple, fast-propagating rifts were formed during the fast seafloor spreading episode in the Cretaceous.