Estructura del cinturón de pliegues y cabalgamientos de Peralta, República Dominicana

Most of the geotectonic units involved in the evolution of the Northern part of the Caribbean Plate can be identified in a geological cross-section through the southern-central part of the Hispaniola Island (South of the Dominican Republic). The cross-section includes from N to S: remnants of the old Caribbean ocean (Loma Caribe Peridotites and Duarte Fm of Upper Jurassic-Lower Cretaceous age), rocks of the Primitive volcanic Island Arc (Lower Cretaceous), the Circum-Caribbean Island Arc (Upper Cretaceous to Eocene), the Peralta thrust and fold Belt and the Azua Neogene Basin. The structure consists of an imbricate thrust system with associated folds, vergent towards the South, that overthrusts the Azua Basin. The thrust system evolved in a forward propagating sequence. The first thrust sheets of the Circum-Caribbean Island Arc possibly formed in Upper Eocene times during sedimentation of the Ocoa Fm in the foredeep (area of the Peralta Belt). Ocoa Fm has a syntectonic character and is associated with the uplift of the Central Mountain Range. Thrusting continued through Oligocene times progressing towards the South. By Lower Miocene times, the Circum-Caribbean Island Arc overthrusts the Peralta Belt (Frontal Thrust of the Tireo Fm). Thrusting in the Peralta Belt continued until Plio-Pleistocene times, as indicated by the age of the rocks in the footwall to the Peralta Belt Frontal Thrust. From Miocene times thrusting was coeval with wrenching that progressively became the dominant tectonic style in the region. The Eocene-Oligocene sedimentary sequences of the Peralta Belt were deposited in a back-arc basin that was subsequently deformed during the change in subduction direction that took place in the northeastern part of the Caribbean Plate in Neogene times. The Neogene Peralta Thrust and Fold Belt may be caused by the indentation of the Beata Ridge into the Circum-Caribbean Island Arc. In this context, the eastern part of the Beata Ridge may have acted as a transform boundary separating the Los Muertos trench from the Peralta Belt. The Peralta Belt accumulated part or all the shortening laterally equivalent to that in Los Muertos accretionary prism

Paleoesfuerzos cenozoicos en el entorno de la falla de Ubierna (Burgos, Cordillera Cantábrica) y norte de la Cuenca del Duero

Se reconstruye la evolución de los campos de esfuerzos durante el Cenozoico en el entorno de la falla de Ubierna, desgarre dextral de dirección NOSE, a partir de 23 muestras de fallas, diaclasas y estilolitos tomadas en unidades del Mesozoico y Mioceno. Se de¿ne un campo de esfuerzos compresivo con s1 orientado N a NNE, activo hasta al menos el Mioceno inferior, en el que algunos tensores extensionales (s1 vertical) con s3 próximo a EO representan episodios de intercambio de los ejes s1 y s2. En el Mioceno superior el campo de esfuerzos cambia a una extensión con trayectorias de s3 próximas a N-S. The evolution of Cenozoic stress ¿elds in the area surrounding the dextral strike-slip, NW-SE striking Ubierna fault is reconstructed from samples of faults, joints and stylolites collected in 23 data sites in Mesozoic and Miocene units. A compressional stress ¿eld with s1 oriented N to NNE is de¿ned, which operated at least until early Miocene time. Extensional tensors (s1 vertical) with s3 oriented close to E-W represent episodes of permutation of the s1 and s2 axes within that stress ¿eld. During the late Miocene, the stress ¿eld changes towards an extensional one with s3 trajectories close to N-S

Metamorfismo y estructura de la Formación Maimón y los Complejos Duarte y Río Verde, Cordillera Central Dominicana: implicaciones en la estructura y la evolución del primitivo Arco Isla Caribeño

The mainly metabasaltic pre-Aptian/Albian basement of the Median Belt of Hispaniola includes the Duarte Complex, the Río Verde Complex and the Maimón-Los Ranchos Formations. In base to mineral assemblages present in metabasic rocks and P-T conditions estimated from thermobarometry, the Río Verde Complex is divided into four metamorphic zones and Zone IV is further subdivided into two. The metamorphic grade increase upward in the structural sequence, from prehnite-pumpellyte facies (Zone I), through greens-chist facies (Zones II and III) and amphibolite facies (Zone IVa), to upper amphibolite facies (Zone IVb), only restricted to Cpx-bearing amphibolites just below the contact with the overlying Loma Caribe Peridotite. The metamorphic field gradient is inverse and of low-P type. The P-T paths documented for Zones IVa and IVb of the Río Verde Complex involve a two-stage prograde evolution: a first event of near isobaric heating in the low-pressure field, typical of sub-ophiolite metamorphic sole rocks and characterized by critical high-grade assemblages; and a second event marked by a medium-pressure overprint of the first-stage metamorphic assemblages following a high-P gradient. These P-T paths are interpreted to result from intra-oceanic thrusting during the closure of a back-arc basin related with the Primitive Caribbean Island Arc and the onset of subduction of arc units in the Aptian/Albian time, which formed the high-pressure metamorphic overprint. The heating and development of an inverted metamorphic gradient in the sub-ophiolite Río Verde Complex, can be genetically related with the hanginwall emplacement of the hot peridotitic slice and the conductive heat transfer downward. The studied sector of the Duarte Complex (metamorphosed oceanic plateau) is divided into three metamorphic zones. Their distribution suggest that there is a temperature increase westward and downward in the structural sequence, from the upper greenschist facies (zone A), through Ep-amphibolite and amphibolite facies (zone B), to upper amphibolite transitional to lower granulite facies (zone C). The metamorphic field gradient is normal and the mid-P type (25-30º C/km). The lowest structural levels of the complex are occupied by the gabro-norites of the La Jautía batholith, which formed in ductile shear zones Grt+Opx-bearing granulites metamorphic assemblages. The 89 Ma date obtained from foliated tonalites (U-Pb in zircons) established an Upper Cretaceous age for the main ductile shearing deformation. However, the deformation is very heterogeneous in the complex, existing regionally wide metamorphic sectors without related foliation development. Therefore, the prograde metamorphism of the Duarte Complex is interpreted to result from moderated thickening of a previously thick oceanic crust, due to the great accumulation of plateau-basalts (30 km). The post-thermal peak P-T paths suggest the unloading and cooling of the complex, during the continuous retrograde development of deformative and mylonitic non-coaxial Sp fabrics (84,6±0,5 Ma; 40 Ar/39 Ar cooling age in syn-Sp muscovite). In summary, the metamorphic rocks of the pre-Aptian/Albian basement units of the Median Belt record different stages in the history of the acretion-obduction of the Duarte plateau with the Caribbean Primitive Island Arc. All these tectonothermal events pre-date the final arc-continent collision between the Caribbean island arc and the Bahamas platform during the Late Cretaceous

Subdivisión geoquímica del Arco Isla Circum-Caribeño, Cordillera Central Dominicana: Implicaciones para la formación, acrecion y crecimineto cortical en un ambiente intraoceánico

The Upper Cretaceous-Eocene Circum-Caribbean island-arc system (AICC) is a complex collage of crustal units or terranes s.l. which have formed and accreted within an intra-oceanic environment since Late Jurassic-Early Cretaceous times. In the Cordillera Central of the Dominican Republic these terranes are represented by several tectonostratigraphic units, that define a pre-Aptian-Albian deformed and metamorphosed basement, over and into which the igneous rocks of the AICC were extruded or intruded. Basement sequences can be subdivided into: (1) a plume-related Duarte terrane (plateau I); (2) a primitive arc-related Maimón-Amina terrane, which includes intra- or back-arc N-MORB units (Río Verde Complex) with a subduction geochemical imprint; and (3) the Loma Caribe peridotite terrane of mantle provenance. Two successive stages of the arc growth are superposed: an Early Cretaceous arc tholeiite stage with boninitic affinities (arc I), and a Late Cretaceous-Eocene calc-alkaline stage (AICC; arc II). The arc I stage is not recorded in the Duarte terrane but is represented in the Maimón-Amina terrane by the Río Verde Complex, the Maimón Forma-tion and the Peralvillo Norte Formation. In the Duarte terrane, the arc II growth stage include the Siete Cabezas Formation (Cenomanian- Maastrichtian, plateau II) and the fill of an intra-arc basin by the Tireo Formation (Cenomanian-Maastrichtian). In the Maimón-Amina terrane, the arc II growth is represented by the Las Lagunas and Peralvillo Sur Formations. The former lies unconformably on rudist-bearing limestone of Albian age (Hatillo Limestone). The Jautía gabbro-norite batholith and the calc-alkaline foliated and non-foliated tonalitic plutons of Late-Cretaceous-Early Eocene age intrude the rocks of the Duarte terrane except the Siete Cabezas Formation. Deformation and metamorphism of the pre-Aptian-Albian basement is a consequence of the collision of the Duarte plateau terrane with the Caribbean primitive island arc (Maimón-Amina terrane), that caused the emplacement of the Duarte terrane with a fragment of oceanic lithosphere (ophiolite). The interpretation of the geological and geochemical data support a tectonomagmatic model, which relates the compositional evolution of the intruded and extruded magmas in this segment of the AICC, with a flip in the subduction polarity under the primitive arc after the Aptian/Albian collision

Upper Cretaceous stratigraphy of the forearc deposits outcropping in the Oriental Cordillera (Dominican Republic)

La sucesión del Cretácico Superior de la Cordillera Oriental de la República Dominicana contiene cerca de 6 km de rocas volcanogénicas sedimentarias y volcánicas depositadas en un sistema de talud sobre el extinto arco volcánico del Cretácico Inferior. Está limitada por dos discordancias que permiten caracterizarla como una secuencia deposicional. La inferior es consecuencia de los procesos de disgregación gravitacional que acompañan la formación del talud submarino; la superior se debe a la truncación subaérea de estructuras contractivas. Las formaciones estratigráficas se agrupan en tres episodios deposicionales: (1) Cenomaniense-Santoniense (Fm Las Guayabas y miembros relacionados) formado por una asociación de grauwacas volcanogénicas, rocas piroclásticas, lavas, lutitas silíceas y calizas pelágicas, que indican la proximidad del arco volcánico, (2) Santoniense formado exclusivamente por silexitas de radiolarios (Fm Arroyo La Yabana), indicando el cese de los aportes clásticos, (3) Santoniense-Maastrichtiense formado por calcilutitas y turbiditas con granos y clastos de carbonatos de plataforma somera y líticos-volcánicos (Fm Río Chavón y Mb Las Auyamas) y, únicamente en el Maastrichtiense, calcarenitas costeras y parches de rudistas sobre montículos de serpentinita (Fm Loma de Anglada). La curva de subsidencia para el Cretácico Superior se inicia con una aceleración alrededor del Cenomaniense que culmina en el Santoniense, se ralentiza en el Campaniense Maastrichtiense y termina con una importante elevación en la base del Paleoceno. La posición de la secuencia deposicional de la Cordillera Oriental respecto al resto de unidades geotectónicas del margen norte de la Placa del Caribe sugiere su deposición en una cuenca de ante-arco.The Upper Cretaceous succession in the Oriental Cordillera of Dominican Republic contains near 6 km of secondary and primary volcaniclastics, deposited in a slope-apron system developed on the extinct lower Cretaceous volcanic-arc. It conforms a depositional sequence, bounded by two angular unconformities: the base unconformity is submarine and results from mass-wasting processes operating in the nascent, oversteeped slope; the top unconformity results from the subaerial truncation of contractive structures. The stratigraphical succession is comprised of three depositional episodes: (1) Cenomanian-Santonian (Las Guayabas Fm and related members) composed of an association of volcanogenic greywackes, pyroclastic rocks, lava flows, silicified lime and pelagic limestones, indicating the proximity of the arc, (2) Santonian episode, made of thin beds of radiolarian chert (Arroyo La Yabana Fm) pointing to the cease of the clastic input from the slope, and (3) Santonian-Maastrichtian composed of calcilutites and coarse-redeposited limestones (Río Chavón Fm and Las Auyamas Mb) and, only in the Maastrichtian, coastal calcarenites and rudist patch reefs lying on serpentinite seamounts (Loma de Anglada Fm). The subsidence curve for the Late Cretaceous starts with an acceleration around the Cenomanian, peaks in the Santonian, decelerates in the Campanian-Maastrichtian, and ends with an important uplift at the base of the Paleocene. The location of the Oriental Cordillera deposits in respect to the other geotectonic units of the northern Caribbean Plate boundary suggest deposition in a fore-arc basin.Unión Europea. Programa SYSMIN (2002-2004)Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu