La secuencia magmática Jurásico Superior-Cretácico Superior en la Cordillera Central, República Dominicana: sección cortical de un arco-isla intraoceánico.

The Late Jurassic-Late Cretaceous magmatic sequence exposed in the central-western sector of the Cordillera Central Dominican Republic, can be divided in five main lithostratigraphic units formed by plutonio, volcanic, volcanoclastic and sedimentary rocks. All rocks have suffered very heterogeneous ductile deformation and low-grade metamorphism with magmatic textures often preserved. From bottom to top, this magmatic sequence is made up of:: (1) Loma Caribe serpentinized peridotites, (2) the N-MORB volcano-plutonic assemblage of El Aguacate, of ophiolitic affinity, (3) the Duarte Complex oceanic plateau, (4) the arc-related volcanic and volcano-sedimentary sequence of the Tireo Formation, intruded by the Loma de Cabrera Batolith, and (5) the massive basaltic flows of Peña Blanca y Nalga de Maco. It is suggested that the magmatic sequence represents the crustal section of an intra-oceanic island arc, which was built onto a proto-caribbean oceanic crust and an overlying Lower Cretaceous oceanic plateau. The sequence is overlain by Upper Cretaceous basalts of the Caribbean oceanic plateau and limestones

The stratigraphy of Sierra de Neiba (Dominican Republic)

La reciente cartografía a escala 1:50.000 de los sectores centrales y meridionales, más desconocidos, de la Sierra de Neiba ha permitido establecer con mayor precisión su estratigrafía. Los materiales más antiguos corresponden a la Unidad de El Manguito, del Cretácico Superior. Son calizas y lutitas pizarrosas con intercalaciones de basaltos que afloran como un fragmento o bloque tectónico de interpretación estructural dudosa en el núcleo de un anticlinal. Por su edad, se considera que esta unidad debe constituir el sustrato de las series paleógenas de la Sierra de Neiba; la composición geoquímica de los basaltos (OIB-basaltos alcalinos intraplaca) sugiere su correlación con la meseta oceánica del Caribe. El registro estratigráfico más o menos continuo comienza en el Eoceno Inferior con el desarrollo de una extensa plataforma carbonatada, relativamente uniforme, que fue el medio de depósito de la Fm Neiba (sensu lato) y sus equivalentes, hasta el Mioceno Inferior. Durante buena parte del Eoceno, estos depósitos carbonatados coexistieron o fueron sustituidos por materiales volcánicos de signatura toleítica a alcalina (OIT a OIA) que se agrupan bajo la nueva denominación de Complejo Volcanosedimentario de El Aguacate de Neiba y se interpretan como generados en un contexto de intraplaca asociados al desarrollo de una pluma mantélica. La sedimentación de la Fm Sombrerito durante el Mioceno muestra los primeros signos de inestabilidad en la región: mientras que en los sectores septentrionales y centrales de la sierra sus facies más típicas se depositan en una cuenca turbidítica, en su extremo suroccidental afloran las calizas arrecifales de su Mb Barahona, propias de ambientes de plataforma somera, que se extienden con gran uniformidad hacia el sur hasta los dominios de la Sierra de Bahoruco. La Unidad de Cortadero, de nueva denominación y equivalente en edad a la Fm Sombrerito, con una posición intermedia entre ambos tipos de facies, puede representar el tránsito entre ellas.The recent 1:50.0000 scale mapping of the central and southern, most unknown, parts of the Sierra de Neiba, has allowed to establish its stratigraphy with higher precision. The oldest materials belong to the El Manguito Unit, of Upper Cretaceous age. They are limestones and shales with interbedded basalts that outcrop as part of a fragment or tectonic block of unknown structural origin in the core of an anticline. In view of its age, this unit may be considered to be the substratum of the Sierra de Neiba Palaeogene formations. The geochemical signature of the basalts (OIB-alkaline intraplate basalts) suggests their correlation to the Caribbean oceanic plateau. The continuous stratigraphic record starts in the Lower Eocene with the onset of an extensive relatively uniform carbonate platform that was the depositional environment for the Neiba Fm (sensu lato) and equivalent units up to the Lower Miocene. During most of the Eocene, these carbonate deposits coexisted with, or were replaced by, volcanic materials of a tholeitic to alkaline signature (OIT to OIA) grouped under the new denomination of El Aguacate de Neiba Volcanosedimentary Complex, and interpreted to originate in an intraplate context under the effect of a mantel plume. The sedimentation of the Sombrerito Fm during the Miocene reveals the first signs of regional instability: whereas in the northern and central areas of the sierra its most typical facies were deposited in a turbiditic basin, in its southwest margin the coral reef limestones of the Barahona Mb represent shallow platform environments that extended farther south to the domains of Sierra de Bahoruco. It is suggested that the Cortadero Unit, with the same age as the Sombrerito Fm and an intermediate position between these two extreme kind of facies, may represent the transition from one to the other.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUERepública Dominicana. Dirección General de MineríaUnidad Técnica de Gestión del programa SYSMINpu

Magmatic relationships and ages of Caribbean Island arc tholeiites, boninites and related felsic rocks, Dominican Republic

International audienceLocated in the Cordillera Oriental of the Dominican Republic, the Early Cretaceous Los Ranchos Fm (LRF) comprises a > 3-km thick sequence of volcanic and volcaniclastic rocks with variable geochemical characteristics, which is intruded by tonalite batholiths, minor gabbro/diorite plutons and mafic dykes. From top to bottom, three main stratigraphic units have been mapped: upper basaltic, intermediate rhyodacitic and lower basaltic. Combined detailed mapping, stratigraphy, geochemistry, Rb–Sr/Sm–Nd isotopic studies and U–Pb/Ar–Ar geochronology show that the mafic rocks of the LRF include boninites and LREE-depleted island arc tholeiites (IAT) in the lower unit, both which appear genetically related, whereas normal IAT occur in the upper unit. The source for these rocks is thought to reflect variably depleted mantle, overprinted by a subduction zone component. Contemporaneous Aptian U–Pb zircon ages were obtained for a rhyodacite from the intermediate unit (116.0 ± 0.8 Ma) and a tonalite of the Zambrana batholith (115.5 ± 0.3 Ma) that intrudes the LRF. The similarity of trace element signatures in both units argues for genetic link between the felsic volcanics of the LRF and the tonalite plutonism. Low-K rhyolites and tonalite batholiths are interpreted as products of secondary melting at the base of thickened early arc crust. 40Ar/39Ar plateau ages of hornblende in most tonalites are Albian (109–106 Ma) and interpreted as final cooling ages, prior to unroofing and growth of unconformable overlying reef limestones of the Hatillo Fm (112–100 Ma). The LREE-depleted IAT and boninites of lower basaltic unit are interpreted to have formed during subduction zone initiation in the Caribbean Island arc, and the normal IAT of the upper unit are thought to represent the subsequent establishment of the volcanic front