Beata Ridge Research Articles

Active Tectonics, Quaternary Stress Regime Evolution and Seismotectonic Faults in Southern Central Hispaniola: Implications for the Quantitative Seismic Hazard Assessment

AbstractPresent‐day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike‐slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE‐directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre‐Early Pleistocene D1 event of NE‐trending compression, which gave rise to the large‐scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan‐Azua basin. This was followed by a near pure strike‐slip D2 stress regime, partitioned into the N‐S to NE‐SW transverse Ocoa‐Bonao‐La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub‐parallel deformation corridors. Shift to D2 strike‐slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard.

Present‐Day Caribbean‐North American Oblique Convergence Through the Ocoa‐Bonao‐La Guacara Fault Zone, Southern Central Hispaniola: A Transition Zone Between Oceanic Subduction and Arc‐Oceanic Plateau Collision

AbstractAccording to GPS measurements, the Caribbean plate is moving east‐northeastward relative to the North American plate at a rate of ∼20 mm/a. This oblique motion is partly accommodated in southern Hispaniola by northward underthrusting/subduction bellow the Muertos submerged accretionary prism and the Peralta fold‐and‐thrust belt. This work investigates the active transition zone that connects Muertos and Peralta: the Ocoa‐Bonao‐La Guacara fault zone (OBFZ). Combined detailed structural analysis at macroscopic and mesoscopic scales, regional magnetic data and seismicity analysis, geomorphic observations, fault‐slip data inversion and geochronology of Quaternary deposits allow to establish the deformation pattern for the OBFZ along southern central Hispaniola. Distinct tectonic regimes have occurred successively in the Neogene, within a consistent regional NE‐trending horizontal shortening: (a) a lower Miocene to Early Pleistocene D1 regime characterized by SW‐directed thrusting that homogeneously affects the region; and (b) an Early/Middle Pleistocene to Holocene D2 regime of strike‐slip to transpressional faulting mainly located along the OBFZ. The change is coeval with the tectonic indentation of the Beata Ridge in the back‐arc region of the Hispaniola microplate. Finally, a Late Pleistocene to Holocene D3 extensional regime has a local development around the Ocoa Bay. Part of the present‐day stress‐field induced by the Beata Ridge collision is accommodated by the OBFZ within the Hispaniola microplate. This fault zone defines the onland transition between oceanic subduction and arc‐oceanic plateau collision. Due to its length and potential to generate large earthquakes, the OBFZ must be considered in the regional seismic hazard assessment.

Chronology and geochemistry of the Caribbean Large Igneous Province in Jamaica

Jamaica has a complex geological history with rocks belonging to the Cretaceous Caribbean Large Igneous Province (CLIP) in the east and Cretaceous oceanic island arc rocks in the centre and west. We present a new geochemical dataset for the CLIP and correlate this dataset and previous datasets using radiolarians and planktic foraminifers to the geological timescale. The palaeontological dating indicates that two phases of plateau activity – ‘main’ phase in the late Turonian-mid Coniacian (c. 92-87 Ma) and an ‘extended’ phase in the Coniacian to mid Campanian (c. 88-75 Ma). These phases are also seen in the Beata Ridge and on the Lower Nicaragua Rise. The geochemistry indicates that both phases are typical large igneous province plateau basalts. The ‘main’ phase has slightly more depleted light rare earth elements than the extended phase, indicating mantle source heterogeneity, and a (Sm/Yb)n >1 indicates a deeper average depth of melting for the ‘main’ phase. The association of the basalts with sediments containing specific microfossil assemblages clearly demonstrates the existence of these two magmatic phases in Jamaica.

Basin modeling of Late Cretaceous / Mio-Pliocene (.) petroleum system of the deep-water eastern Colombian Basin and South Caribbean Deformed Belt

Previous interpretation of 2D and 3D seismic reflection data have shown widespread, direct hydrocarbon indicators from deep-water successions of the eastern Colombian Basin (ECB) and adjacent South Caribbean Deformed Belt (SCDB) that suggest the presence of an extensive - but poorly defined - petroleum system. We integrate Rock-Eval analysis, seismic interpretation, and 1D/2D thermal and basin modeling to better understand the origin of gas chimneys and bright spots identified in the ECB. Our dataset consists of 36 Rock-Eval samples of Coniacian to Santonian source rocks from the DSDP well sites 153, 151, and 146 located in the Beata Ridge tied to a 270 km-long composite 2D seismic line covering the ECB. Rock-Eval analyses reveal intervals of immature source rocks containing 1) kerogen types II and III; 2) an average TOC of 3.70% with a maximum TOC of 11.4%; 3) an average HI of 241; and 4) an average OI of 124. Seismic interpretation reveals: 1) wedging of post-Coniacian, organic-rich successions from the Beata Ridge (35–73 m thick) towards the ECB (500–1700 m thick); 2) Late Cretaceous to Eocene slow sedimentation rate of 38 m/my, followed by faster Oligocene to Recent sedimentation rate of 149 m/my from the Magdalena River; and 3) Late Oligocene to Recent thrusting and propagation of the SCDB. Thermal and basin modeling show: 1) mature Cretaceous source rocks in the SCDB and ECB; 2) Miocene to Pliocene, Magdalena Fan-derived deltaic and turbiditic reservoir and seal rocks, and Plio-Pleistocene sealing mass transport deposits.; 3) Late Oligocene to present-day trap formation related to thrust front structures, compaction folds, and stratigraphic traps; 4) hydrocarbon expulsion since Pliocene times; 5) vertical and lateral up-dip seaward migration occurs in the ECB while a secondary landward migration takes place toward the SCDB; and 6) hydrocarbon accumulation and preservation may be affected by remobilization due to biodegradation in the ECB and trap breaching in the SCDB.

Architecture and development of the Magdalena Submarine Fan (southwestern Caribbean)

Submarine fans are the largest sediment accumulations on Earth and are key to study the sediment-transfer zone between terrestrial source area and deep-sea depositional sink. They provide information of past climate, tectonics, carbon global inventory, and can be prolific hosts for oil/gas resources. In this paper, we present, for the first time, an analysis of the entire Magdalena Submarine Fan (MSF), from the shelf break to the distal domain, based on ~224,000 km2 of multibeam bathymetry, as well as backscatter, subbottom profiler and regional/local seismic reflection data recently acquired in southwestern Caribbean Sea. The aim is to describe in detail the MSF morphology and depositional architecture, propose a fan segmentation landform assemblage, and determine its extent within the deep basin. Three fan segments are identified: upper, middle and lower fans. The upper fan extends from the coastline to a depth of ~3000 m. Its eastern sector is characterized by a canyon system off the present-day mouth of the Magdalena River, through which most of the sediments are transported downslope to be deposited in intra-slope basins bounded by structural highs of the South Caribbean Deformed Belt. The western upper fan is characterized by distinct channel-levee complexes that are partially removed by mass transport complexes that originated near the continental shelf edge. The upper to middle fan transition is marked by a decrease in regional gradient from 1° to about 0.3° and local relief, a change from large, irregular sediment waves to more regular waves that slowly decrease in amplitude downslope, and the appearance of erosional megascours. The middle fan bedform assemblage evidences the presence of a channel-lobe transition zone in this sector of the MSF, separating well-defined, upper fan channels from lower fan depositional lobes. The middle to lower fan transition occurs between ~3800 and ~3950 m and is defined by a further decrease in gradient and by a change from sediment waves to planar parallel-bedded reflectors on subbottom profiles. The lower fan extends to a maximum depth of ~4250 m and is characterized by an almost flat seabed (slope of 0.05°), interrupted by a few isolated bathymetric highs and low-relief channels (<5 m deep). The entire area of the lower fan is interpreted as an area of turbidity current deposition, with relatively sandy sediments in the south and west giving way to muddier sediments in the northeast, which could correspond to distal fan lobes. The identification of four regional seismic facies related to MSF sedimentation allowed us to constrain the fan extent in the southwestern sector of the Caribbean. Distally, within the Colombia Basin the fan terminates against areas of elevated seafloor (Kogi-Coyaima and Quimbaya seamounts, Aruzi and Ticuna hills, and Beata Ridge), which have acted as barriers to sedimentation. Nevertheless, it was determined that the MSF extends beyond the Colombia Basin and locally reaches the Lower Nicaraguan Rise. In this new scenario, we established that the MSF is much more extensive than previously recognized, with an area of ~237,000 km2, which puts it among the World's largest submarine fans.

Age and geochemistry of the Beata Ridge: Primary formation during the main phase (~89 Ma) of the Caribbean Large Igneous Province

The Caribbean Large Igneous Province (CLIP), a Cretaceous oceanic flood basalt province, presumably formed at the initiation of the Galápagos hotspot. During the M81 cruise of the German R/V METEOR, we sampled the Beata Ridge, a prominent submarine structure in the Caribbean Sea belonging to the CLIP. The ridge offers the opportunity to directly sample basement sequences of the central, submarine part of the CLIP, complementing numerous studies of accreted CLIP sequences exposed on land around the margins of this LIP. The majority of the recovered Beata Ridge samples are volcanic, implying that at least parts of the Beata Ridge were formed during a large extrusive event in contrast to previous assumptions that the structure is primarily composed of intrusive rocks. Several stratigraphically controlled profiles were sampled along the western slope of the Beata Ridge using the remotely operated vehicle (ROV) Kiel 6000 and revealed variously alternating sequences of magmatic rocks (lavas, pillow breccias, tuffs and gabbros) and sediment fields. We report new 40Ar/39Ar age and geochemical (major and trace element, Sr-Nd-Hf-Pb isotope) data for the recovered magmatic samples. Although the 40Ar/39Ar analyses display partially disturbed age spectra, they suggest an age range of 92.4–76.9 Ma. Thus our age data show for the first time that the Beata Ridge also formed during the main magmatic stage of the CLIP (~95–83 Ma). Previous studies suggested that the Beata Ridge was formed during a second, lower-volume magmatic phase of the CLIP (~81–71 Ma), possibly related to decompression melting during an extensional phase in the Caribbean. Most samples display relatively flat chondrite-normalized rare earth element (REE) patterns commonly observed throughout the CLIP, but light REE enriched and depleted compositions are also present. The occurrence of enriched and depleted incompatible element and radiogenic isotope signatures implies a heterogeneous mantle source region, as is observed for other LIPs worldwide. Since a high degree of geochemical variability is observed over short stratigraphic intervals within the ROV profiles, melt homogenization did not operate as effectively as commonly assumed for LIPs. Instead the plume head probably preserved some domains of enriched and depleted components. Most of the melts during the main stage have intermediate compositions (with flat REE patterns), representing mixtures of the enriched and depleted components.

Seismotectonics of south-west Dominican Republic using recent data

The Dominican Republic has a high level of seismic activity, and a new seismic network has been installed to improve the detection of earthquakes. The network has been operated by Instituto Politecnico Loyola since 2012. It uses six new stations of its own, as well as 17 other stations publically available. In this study, we investigate in particular the south-west of the country where no seismic stations have been operating before. We find an area, SE of the Enriquillo Plantain Garden fault (responsible for the 2010 Haiti M7.0 earthquake), with a high seismic activity (M = 2–4) compared to the surrounding area. This shallow seismicity (except two events around 40 km depth) is not seen in any global catalogs, and it does not seem to be associated with any known faults. However, the region has been under rapid recent uplift since margins between hills and valleys are filled with massive alluvial fans. We made 24 new fault plane solutions using P-polarities and S/P amplitude ratios. The solutions show mainly reverse mechanisms and the P-axis directions are mainly NNE oriented, which is in agreement with a published strain direction from GPS measurements. We conclude that the main cause of the seismicity in our study area is the push of the Beata Ridge against Enriquillo basin and the rest of the Gonave microplate, reflected in the mainly reverse focal mechanisms.

The basaltic volcanism of the Dumisseau Formation in the Sierra de Bahoruco, SW Dominican Republic: a record of the mantle plume magmatism of the Caribbean Large Igneous Province

The Dumisseau Formation outcropping in the Sierra de Bahoruco offers the opportunity for studying on land the mantle plume magmatism generator of the Caribbean Large Igneous Province (CLIP) during the Late Cretaceous. It consists of a sequence of about 1.0-1.5 km-thick mainly composed of mafic basaltic flows and pyroclastic deposits, with subordinated volcanogenic sedimentary deposits and syn-volcanic doleritic sills and dikes. All the volcanic rocks were erupted or re-sedimented in relatively deep-marine conditions, as evidenced by the rare interbedded chert and pelagic limestone. On the basis of the MgO, TiO2 and incompatible trace elements contents three geochemical groups have been identified in the Dumisseau Formation: low-Ti tholeiites; high-Ti or transitional basalts; and high-Ti and LREE alkaline basalts. Geochemical modelling indicates a derivation from melts generated and incorporated at different depths in the mantle, which is consistent with the processes that take place during the rise of a mantle plume beneath the oceanic crust. Two 40Ar/39Ar whole-rock ages indicate the extrusion of magmas at least in the 92-74 Ma time interval (Turonian-Coniacian boundary to Maastrichtian), resulting coeval with the formation of the CLIP. As a result, the Dumisseau Formation is an emerged fragment of the CLIP, with which it must have continuity through the Beata Ridge. These rocks are unconformably overlain by carbonate red algae facies of the middle-upper Eocene, constituting the volcanic basement of the Sierra de Bahoruco.

Crustal and upper mantle structure beneath the Gulf of Mexico and the Caribbean Sea from Rayleigh‐wave analysis

The elastic structure beneath the Gulf of Mexico and the Caribbean Sea is presented in this paper by means of S‐velocity maps, for depths ranging from 0 to 350 km, determined from Rayleigh‐wave analysis. The S‐velocity mapping, for the depth range from 0 to 5 km, shows clearly the distribution of sedimentary basins of the study area. For the depth range from 5 to 35 km, the higher S‐velocity values are associated to the areas in which the crust is thinner (oceanic crust). For the Caribbean Plate, which consists of the Venezuelan and Colombian basins separated by the Beata Ridge, a differentiation between both basins is possible in terms of S‐velocity. The thickening of the Caribbean crust (observed in the southern part of the study area), due to the Caribbean–South America plate interactions, is confirmed by the S‐velocity mapping; thickened crust is characterized by S‐velocities lower than those for the upper mantle. For depths greater than 35 km, the S‐velocity presents its higher values at the older regions of the study area, while the younger or active regions are imaged with low S‐velocity. Finally, a new and very interesting feature presented in this study is the location and thickness of the lithosphere–asthenosphere system. On the other hand, this study provides the mapping necessary to locate the deep geologic structures, present in the study area, which tectonic and geologic evolution is wished to determine, allowing also to know the nature and type of the crust and upper‐mantle structure beneath this area. Once this knowledge is reached, an evolutionary model can be developed. This study is especially interesting for areas in the Gulf of Mexico that are hidden beneath near‐opaque, complex, and extensive allochthonous salt bodies, which make it difficult to use other seismic exploration techniques such as seismic refraction or reflection techniques.

Curie point depth in the SW Caribbean using the radially averaged spectra of magnetic anomalies

We have estimated the Curie Point Depth (CPD) using the average radial power spectrum in a tectonically complex area located in the SW Caribbean basin. Data analyzed came from the World Digital Magnetic Anomaly Map, and three methods have been used to compare results and evaluate uncertainties: Centroid, Spectral Peak, and Forward Modeling. Results show a match along the three methods, suggesting that the CPD values in the area ranging between 6km and 50km. The results share the following characteristics: A) High values (>30km) are in continental regions; B) There is a trend of maximum CPD values along the SW-NE direction, starting from the Central Cordillera in Colombia to the Maracaibo Lake in Venezuela; C) There is a maximum CPD at the Sierra Nevada de Santa Marta (Colombia) as well as between Costa Rica - Nicaragua and Nicaragua - Honduras borders. The lowest CPD values (<20km) are associated with the coastal regions and offshore. We also tested results by estimating the geothermal gradient and comparing measured observations of the study area. Our results suggest at least five thermal terrains in the SW Caribbean Basin: A) The area that is comprising the Venezuela Basin, the Beata Ridge and the Colombia Basin up to longitude parallel to the Providencia Throat. B) The area that includes zones to the north of the Cocos Ridge and Panam Basin up to the trench. C) The orogenic region of the northern Andes and including areas of the Santa Marta Massif. D) The continental sector that encompasses Nicaragua, northern Costa Rica and eastern of Honduras. E) Corresponds to areas of the northern Venezuela and Colombia, NW of Colombia, the Panamanian territory and the transition zones between the Upper and Lower Nicaragua Rise.

The cladorhizid fauna (Porifera, Poecilosclerida) of the Caribbean and adjacent waters.

The carnivorous sponge family Cladorhizidae has been subject to several recent studies, yet the cladorhizid fauna of the Caribbean and adjacent areas remain comparatively poorly known. In this article we provide a description of the novel species Abyssocladia polycephalus sp. nov. from the Muir Seamount NE of Bermuda, belonging to the mainly Pacific genus Abyssocladia, and Asbestopluma (Asbestopluma) caribica sp. nov. from the Beata Ridge. Additionally, we provide a re-description of the poorly known species Chondrocladia (Chondrocladia) verticillata Topsent, 1920, and compare this species with the closely related species C. (C.) concrescens Schmidt, 1880. Finally, we provide a brief overview of the carnivorous sponges known from the Gulf of Mexico, Caribbean Sea and adjacent Atlantic Ocean.

The basaltic volcanism of the Dumisseau Formation in the Sierra de Bahoruco, SW Dominican Republic: A record of the mantle plume-related magmatism of the Caribbean Large Igneous Province

The basaltic volcanism of the Dumisseau Fm in the Sierra de Bahoruco, SW Dominican Republic, offers the opportunity to study, on land, the volcanism of the Caribbean Large Igneous Province (CLIP). It consists of an at least 1.5km-thick sequence of submarine basaltic flows and pyroclastic deposits, intruded by doleritic dykes and sills. Three geochemical groups have been identified: low-Ti tholeiites (group I); high-Ti transitional basalts (group II); and high-Ti and LREE-enriched alkaline basalts (group III). These geochemical signatures indicate a plume source for all groups of basalts, which are compositionally similar to the volcanic rocks that make up various CLIP fragments in the northern region of the Caribbean Plate. Trace element modelling indicates that group I magmas are products of 8–20% melting of spinel lherzolite, group II magmas result 4–10% melting of a mixture of spinel and garnet lherzolite, and group III basalts are derived by low degrees (0.05–4%) of melting of garnet lherzolite. Dynamic melting models suggest that basalts represent aggregate melts produced by progressive decompression melting in a mantle plume. There is no compositional evidence for the involvement of a Caribbean supra-subduction zone mantle or crust in the generation of the basalts. Two 40Ar/39Ar whole-rock ages reflect the crystallisation of group II magmas at least in the late Campanian (~74Ma) and the lower Eocene (~53Ma). All data suggest that the Dumisseau Fm is an emerged fragment of the CLIP, which continues southward through the Beata Ridge

Modeling the Crust and Upper Mantle in Northern Beata Ridge (CARIBE NORTE Project)

The complex tectonic region of NE Caribbean, where Hispaniola and Puerto Rico are located, is bordered by subduction zone with oblique convergence in the north and by incipient subduction zone associated to Muertos Trough in the south. Central Caribbean basin is characterized by the presence of a prominent topographic structure known as Beata Ridge, whose oceanic crustal thickness is unusual. The northern part of Beata Ridge is colliding with the central part of Hispaniola along a transverse NE alignment, which constitutes a morphostructural limit, thus producing the interruption of the Cibao Valley and the divergence of the rivers and basins in opposite directions. The direction of this alignment coincides with the discontinuity that could explain the extreme difference between west and east seismicity of the island. Different studies have provided information about Beata Ridge, mainly about the shallow structure from MCS data. In this work, CARIBE NORTE (2009) wide-angle seismic data are analyzed along a WNW-ESE trending line in the northern flank of Beata Ridge, providing a complete tectonic view about shallow, middle and deep structures. The results show clear tectonic differences between west and east separated by Beata Island. In the Haiti Basin area, sedimentary cover is strongly influenced by the bathymetry and its thickness decreases toward to the island. In this area, the Upper Mantle reaches 20 km deep increasing up to 24 km below the island where the sedimentary cover disappears. To the east, the three seamounts of Beata Ridge provoke the appearance of a structure completely different where sedimentary cover reaches thicknesses of 4 km between seamounts and Moho rises up to 13 km deep. This study has allowed to determine the Moho topography and to characterize seismically the first upper mantle layers along the northern Beata Ridge, which had not been possible with previous MCS data.

Morphostructure at the junction between the Beata ridge and the Greater Antilles island arc (offshore Hispaniola southern slope)

Abstract Oblique convergence between the Caribbean plate's interior and the inactive Greater Antilles island arc has resulted in the collision and impingement of the thickened crust of the Beata ridge into southern Hispaniola Island. Deformation resulting from this convergence changes from a low-angle southward-verging thrust south of eastern Hispaniola, to collision and uplift in south-central Hispaniola, and to left-lateral transpression along the Southern peninsula of Haiti in western Hispaniola. Using new swath bathymetry and a dense seismic reflection grid, we mapped the morphological, structural and sedimentological elements of offshore southern Hispaniola. We have identified four morphotectonic provinces: the Dominican sub-basin, the Muertos margin, the Beata ridge and the Haiti sub-basin. The lower slope of the Muertos margin is occupied by the active Muertos thrust belt, which includes several active out-of-sequence thrust faults that, were they to rupture along their entire length, could generate large-magnitude earthquakes. The interaction of the thrust belt with the Beata ridge yields a huge recess and the imbricate system disappears. The upper slope of the Muertos margin shows thick slope deposits where the extensional tectonics and slumping processes predominate. The northern Beata ridge consists of an asymmetrically uplifted and faulted block of oceanic crust. Our results suggest that the shallower structure and morphology of the northern Beata ridge can be mainly explained by a mechanism of extensional unloading from the Upper Cretaceous onward that is still active residually along the summit of the ridge. The tectonic models for the northern Beata ridge involving active reverse strike–slip faults and transpression caused by the oblique convergence between the Beata ridge and the island arc are not supported by the structural interpretation. The eastern Bahoruco slope an old normal fault that acts as a passive tear fault accommodating the sharp along-strike transition from low-angle thrusting to collision and uplifting.

Late Cretaceous‐Miocene diachronous onset of back thrusting along the South Caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth

The Venezuelan basin is obliquely subducted to the east‐southeast beneath the continental South American plate at the east‐west‐trending South Caribbean deformed belt (SCDB), a 50–100‐km‐wide wedge of accreted sedimentary rocks derived both from offscraping of the 0.5 to 1 km‐thick sedimentary cover of the subducting Venezuelan basin and from incorporation of clastic sediments derived from the continental margin of South America. In this paper we describe the structure and sequence stratigraphy of five Late Cretaceous to recent sedimentary sequences overlying a 230,000 km2 area of the southern Venezuelan basin and Beata Ridge. The data set includes 5900 km of 2D seismic reflection data that are tied to lithologic and age data taken from DSDP sites 146/149 and 150 in the central part of the Venezuelan basin. We use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the SCDB to determine the age of the diachronous west‐to‐east initiation of thrusting and subduction at the SCDB. The onset of subduction in the SCDB corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic Caribbean arc and the South American continent. This correlation in the age of deformation indicates that collision between the Caribbean arc and the South American continent led to subduction polarity reversal, a process that is commonly observed at various stages of tectonic evolution in other areas of active, arc‐continent collision including Japan and Sunda.

Submarine volcanic stratigraphy and the Caribbean LIP's formational environment

Abstract In 1995, R/V Maurice Ewing cruise EW9501 collected 5200 km of high-quality multichannel reflection profiles and 104 wide angle sonobuoy profiles in the Venezuelan Basin and over the Beata Ridge. These data provide images of the entire Caribbean crust, from seafloor to Moho, and verify earlier models of a two-‘layer’ crust. The EW9501 data also image the internal structure of these layers, revealing previously unseen features. The upper crustal ‘layer’ is actually a complex sequence, whose stratigraphy is analysed to show that the thickest part of the Caribbean volcanic plateau was experiencing east–west compressional deformation during the last stages of its emplacement.

The Caribbean: an oroclinal basin?

Abstract Tightly curved mountain belts are prominent features of global topography. Typically, these ‘oroclines’ occur in areas of regional compression but enclose basins where extension has been contemporaneous with outward directed thrusting in the orogens. Examples of such basin–orogen pairs include the Alboran Sea–Gibraltar Arc, Tyrrhenian Sea–Aeolian Arc, Aegean Sea–Hellenic Arc and Pannonian Basin–Carpathian Arc, all in the western Tethys but matched in the eastern Tethys by the Banda Sea and Outer Banda Arc. The development of the basins has been variously explained by gravitational collapse of rapidly elevated mountain blocks and by extrusion prompted by asthenopheric flows, but it is not even universally agreed that similar processes have operated in all cases. Critics have cited gross differences in volcanic activity (absent from the Gibraltar Arc, modest in the Carpathians but intense in other examples) and in the presence or absence of recognizable Wadati–Benioff Zones. The superficial similarities between the Caribbean Sea–Antilles Arcs and typical oroclinal basin–orocline pairs have recently been invoked in support of an in situ Caribbean evolutionary model, even though the disputed origins of oroclines limit their reliability as analogues. The Caribbean's considerably greater area further emphasizes the need for caution, while the most obvious objection to identifying it as a member of the oroclinal group is its very long history. Oroclinal basins typically pass from initiation to effective stabilization in a few tens of millions of years, whereas the original Caribbean oceanic crust, which is now bounded to the east and west by active subduction zones, was probably formed in the Jurassic. Rather than invoking an overall common origin for the Caribbean and the Tethyan basins, it is more useful to look for shared causes of specific individual similarities. The impact of a rigid block might be as effective in imposing curvature on a mountain belt as rapid expansion in an adjacent area. However, it does seem that the case for the crust of the Caribbean being typical of oceanic large igneous provinces (LIPs) may have been overstated and, in the light of oroclinal analogues, that some features of the still poorly understood Beata Ridge and Lower Nicaragua Rise may be most easily explained by east–west extension promoted by the convergence between North and South America.

Prolonged Magmatic and Tectonic Development of the Caribbean Igneous Province Revealed by a Diving Submersible Survey

Using the diving submersible survey NAUTICA we investigated the central part of the Caribbean large igneous province (CLIP) to observe and sample internal portions of this proposed oceanic plateau. Most of the samples are gabbroic and doleritic rocks; basalts are scarce. Radiometric dating by 40Ar/39Ar incremental heating experiments indicate that the intrusive rocks are Campanian in age (81–75 Ma). In some places these intrusive rocks underlie older Santonian (85–83 Ma) extrusive basaltic rocks, suggesting that the Campanian rocks represent a sill injection and an underplating episode. Results of the diving program supplemented by information from ODP and DSDP drilling sites document a 20 m.y. period (94–75 Ma) of igneous activity in the submerged portion of the Caribbean large igneous province (CLIP). In the northern part of the Beata Ridge late Campanian and/or post Campanian uplift is documented by prominent Maastrichtian (71–65 Ma) erosion and the establishment of a Paleocene-middle Eocene (65–49 Ma) carbonate platform. During and after the uplift an extensional period is indicated by seismic images and the subsidence (3 km depth) of the carbonate platform. Paleocene ages (55–56 Ma) determined on some volcanic samples are attributed to localised decompression mantle melting that accompanied the extension. We document a prolonged period of magmatic and tectonic events that do not fit with the current models of short-lived plateau formation during mantle plume initiation but shares many similarities with the constructional histories of other oceanic large igneous provinces.

A Complex History for the Caribbean Plateau: Petrology, Geochemistry, and Geochronology of the Beata Ridge, South Hispaniola

Abstract The Beata Ridge is a prominent SSW‐trending topographic structure in the central Caribbean basin. It is characterized by unusually thick oceanic crust (up to 20 km) and is believed to form part of the Caribbean oceanic plateau. Samples recovered by submersible during the Nautica‐Beata cruise show the ridge to be composed mainly of gabbros, dolerites, and rare pillow basalts. Textures, which vary significantly, reflect differences in cooling rates and suggest a subsurface, hypabyssal environment. Major‐element compositions of gabbros and dolerites plot on simple trends that correspond to fractional crystallization of olivine, clinopyroxene, and plagioclase. Trace‐element ratios are close to chondritic [(Nb/Zr)N 0.85–1.1] and rare earth element patterns (REE) are almost flat [(La/Yb)N 0.63–1.02]. The source, however, was isotopically depleted (eNd +7.4 to +9.5). To explain these geochemical features, we propose that the magmas formed through pooling of fractional melts of spinel peridotite. The rar...

Plate boundary readjustment in oblique convergence: Example of the Neogene of Hispaniola, Greater Antilles

The Haitian fold‐and‐thrust belt is the major mountain belt of Haiti (western part of Hispaniola, Greater Antilles) and resembles a compressive restraining bend between the two major faults which have driven the opening of the Cayman Basin since the Eocene. During the rifting stage, from the middle to the late Eocene, this area underwent an extensional evolution with fissural volcanic activity along NE‐SW tilted blocks. The Haitian fold‐and‐thrust belt was constructed from the Early Miocene until the Present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks, which was propagating to the southwest. During the construction of the wedge, piggyback basins were formed and progressively uplifted. During the late Neogene, convergence is localized in the Cul‐de‐Sac‐Enriquillo trough where the active front proceeds southward onto the Beata ridge. In this area, Miocene to Quaternary wrench structures of the lower plate, like the Southern Peninsula and the Enriquillo‐Plantain Garden faults, are reactivated as normal faults, owing to the loading of the fold‐and‐thrust belt.