Caribbean-South America Plate Boundary Research Articles

U–Pb detrital zircon age patterns of Cenozoic clastic sedimentary rocks in Trinidad and its implications

The Cenozoic evolution of northern South America can be simplified as a diachronous, west-to-east change from north-facing passive margin, to active convergence and transcurrent plate margin. As the current eastern end of the Caribbean-South America plate boundary, the Trinidad area records the most recent tectonic regime transition. Documenting the provenance of Cenozoic clastic rocks in Trinidad provides insights into the spatial and temporal relationships between mountain range uplifting, sediment dispersal, and drainage system development along the eastern end of the Caribbean-South American plate boundary. Four Eocene to Pliocene age outcropping sandstone samples were collected from Trinidad and 545 detrital zircon grains were analyzed using the U–Pb LA-ICP-MS method. A total of 404 analyses with less than 10% discordance were used for the final interpretation. Results show that the age distribution of the Eocene to the Early Oligocene samples is very restricted and dominated by Precambrian age grains with age peaks at ~1400Ma, ~1800Ma, and ~2000Ma, typically derived from the Guyana Shield. In contrast, the Late Oligocene and younger samples show much broader and mixed age distribution that includes Mesozoic, Paleozoic, and Precambrian peaks. This age shift was interpreted as arriving of the Great Caribbean Arc and oblique collision between the South America and Caribbean plates. Continuing collision uplifted the Andes belts to the west. The Eastern Cordillera of Colombia, the Merida Andes, and the northern Venezuela coastal ranges then became the second primary sources. Offshore sedimentation switched from the passive margin with multiple small drainage systems to the active convergent and transcurrent plate margin with a single large river-dominated delivery system.

From arc-continent collision to continuous convergence, clues from Paleogene conglomerates along the southern Caribbean–South America plate boundary

A Paleogene conglomeratic-sandy succession preserves the complex record of arc-continent collision, orogen collapse and basin opening, followed by inversion related to renewed oblique convergence. This record is unique because both arc and continental margin are now severely fragmented and only partially exposed along the southern Caribbean–South American boundary in northern Colombia. We studied these clastic sequences in the San Jacinto deformed belt using an integrated provenance study that includes conglomerate clast counting, geochemistry and U–Pb and Hf isotopic analysis in magmatic clasts, together with sandstone petrography, heavy mineral analysis and detrital zircon U–Pb geochronology. The record of events extracted from these coarse clastic rocks includes the formation and approach of an allochthonous Upper Cretaceous intra-oceanic arc active from 88Ma until 73Ma. This arc collides against the upper Paleozoic to Triassic continental margin after 73Ma, but before late Paleocene times. Poorly exposed remnants of serpentinized peridotites and middle pressure metamorphic detritus are related to closure of an intervening oceanic basin between the continent and the colliding arc. This orogen was emerged in late Maastrichtian–early Paleocene, and then collapsed as recorded by the thick upper Paleocene and younger succession of the San Jacinto deformed belt where the coarse clastics, subject of this study, are exposed.Orogenic collapse may have been the result of subduction zone flip, with incipient subduction of the buoyant Caribbean Plate under South America.

Late Cretaceous–Paleocene metamorphic evolution of the Sierra Nevada de Santa Marta: Implications for Caribbean geodynamic evolution

Abstract A Late Cretaceous–Paleocene metamorphic event in the Santa Marta massif (northern Colombia) is characterized by a P – T path with a pressure increase after an initial temperature increase or temperature increasing simultaneously with pressure. In either case, this path indicates loading of pre-heated crust in agreement with the proposed models for the origin of the Caribbean plate and with the current configuration of the Caribbean–South America plate boundary. The P – T path constructed in a pelitic schist from the inner Santa Marta metamorphic belt indicates that garnet grew during a loading event that caused a pressure increase of up to 1.5 kbar in a subduction setting. Sample P – T path and Santa Marta massif tectonic features are compatible with metamorphism on an accretionary wedge with heating prior to loading or synchronous loading and thermal relaxation during thickening of the wedge, this could result from a sedimentary pile accumulated in an anomalously hot oceanic crust. P – T path is also compatible with low angle subduction similar to the current configuration of the subduction of the Caribbean plate below the South America plate and to extensive retrograde metamorphism most likely related to exhumation.

Gravity inversion using seismically derived crustal density models and genetic algorithms: an application to the Caribbean-South American Plate boundary

SUMMARY Crustal density models derived from seismic velocity models by means of velocity–density conversions typically reproduce the main features of the observed gravity anomaly over the area but often show significant misfits. Given the uncertainty in the relationship between velocity and density, seismically derived density models should be regarded as an initial estimate of the true subsurface density structure. In this paper, we present a method for estimating the adjustments necessary to a seismically derived density model to improve the fit to gravity data. The method combines the Genetic Algorithm paradigm with linear inversion as a way to approach the non-linear and linear aspects of the problem. The models are divided into three layers representing the sedimentary column, the crystalline crust and the lithospheric mantle; the depths of these layers are determined from the seismic velocity model. Each of the layers is divided into a number of provinces and a density adjustment (Δρ) value is found for each province so that the residual gravity (difference between the observed gravity anomaly and the anomaly calculated for the seismically derived model) is minimized while keeping Δρ between predefined bounds. The preferred position of the province boundaries is found through the artificial evolution of a population of solutions. Given the stochastic nature of the algorithm and the non-uniqueness of the problem, different realizations can yield different solutions. By performing multiple realizations we can analyse a set of solutions by taking their mean and standard deviation, providing not only an estimate of the Δρ distribution in the subsurface but also an estimate of the associated uncertainty. Synthetic tests prove the ability of the algorithm to accurately recover the location of province boundaries and the Δρ values for a known model when using noise-free synthetic data. When noise is added to the data, the algorithm broadly recovers the features that define the known model despite greater standard deviations of the solutions and the occurrence of artefacts in the mean solutions. The algorithm was applied to four profiles across the Caribbean–South America Plate boundary. Some general patterns in the distribution of Δρ were observed consistently in the profiles and are correlated with the interpretations of the velocity models. Positive Δρ values in the sedimentary layer, negative Δρ values for island arc and extended island arc crust with an abrupt change to positive values in South American crust, and positive values in the mantle under the continent and island arc with a transition to negative values under the Caribbean oceanic crust.

Neogene–Quaternary tectonic evolution of the Leeward Antilles islands (Aruba, Bonaire, Curaçao) from fault kinematic analysis

Aruba, Bonaire, and Curaçao are islands aligned along the crest of a 200-km-long segment of the east–west-trending Leeward Antilles ridge within the broad Caribbean–South America plate boundary zone presently characterized by east–west, right-lateral strike-slip motion. The crust of the Leeward Antilles ridge represents the western segment of the Cretaceous–early Cenozoic Great Arc of the Caribbean, which obliquely collided, with the continental margin of northern South America in early Cenozoic time. Following the collision, the ridge was affected by folding and was segmented by oblique, northwest-striking normal faults that have produced steep-sided, northwest-trending, elongate islands and narrow shelves separated by deepwater, sediment-filled and fault-controlled basins. In this paper, we present the first fault slip observations on the Neogene carbonate rocks that cover large areas of all three islands. Our main objective is to quantify the timing and nature of Neogene to Quaternary phases of faulting and folding that have affected the structure and topography of this area including offshore sedimentary basins that are being explored for their petroleum potential. These data constrain three fault phases that have affected Aruba, Bonaire, and Curaçao and likely the adjacent offshore areas: 1) NW–SE-directed late Paleogene compression; 2) middle Miocene syndepositional NNW–SSE to NNE–SSW extension that produced deep rift basins transverse to the east–west-trending Leeward Antilles ridge; and 3) Pliocene–Quaternary NNE-trending compression that produced NW–SE-trending anticlines present on Aruba, Curaçao and Bonaire islands. Our new observations – that include detailed relationships between striated fault planes, paleostress tensors, and bedding planes – show that prominent bedding dips of Neogene limestone on Aruba, Bonaire and Curaçao were produced by regional tectonic shortening across the entire Leeward Antilles ridge rather than by localized, syndepositional effects as proposed by previous workers. We interpret Pliocene–Quaternary NNE-directed shortening effects on the Leeward Antilles ridge as the result of northeastward extrusion or “tectonic escape” of continental areas of western Venezuela combined with southeastward shallow subduction of the Caribbean plate beneath the ridge.

Crustal thickness variations in Venezuela from deep seismic observations

The Caribbean–South America plate boundary zone is a complex zone of plate interactions, forming thrust belts and foreland basins in northern Venezuela. Within the framework of the BOLIVAR and GEODINOS projects, the geodynamics of plate interactions is being investigated using interdisciplinary geological and geophysical methods. Here, we focus on the results of the land based active seismic observations done in 2004 along four deep seismic wide angle profiles, acquired perpendicular to the Caribbean–South America plate boundary in northern Venezuela between longitudes 63° W and 70° W, and ranging from about latitudes 12 °N to about 9 °N. The mostly unreversed profiles provide information on the crustal structure from the oceanic-transitional crust on the southern border of the Caribbean plate to the continental crust of the Caribbean Mountain System and their associated foreland basins, which are bordered to the south by the Guayana Shield, which corresponds to stable South America plate. The derived crustal thickness oscillates around 35 km along the coastline, corresponding to the Caribbean Mountain System, and decreases only slightly towards the Leeward Antilles. To the south, in the area of the Eastern Venezuela Basin, crustal thickness reaches 40 km, increasing towards the Guayana Shield to 45 km. Nevertheless, there are two regions of anomalous crustal thickness, proven by arrivals from the lower crust and the Moho discontinuity. In the eastern part of the Eastern Venezuela Basin, crustal thickness reaches up to 50 km, with high velocity anomalies within the lower crust, which are interpreted as reworked lower crustal and upper mantle material, associated to the plate interactions of the South American and the Caribbean plates. The second anomalous zone is a remarkable crustal thinning from 35 km to 27 km in the Falcón Basin in western Venezuela, which extends eastwards into the Bonaire Basin, as documented by PmP reflections derived from land shots, and observations of the air gun blasts on the stations of the Venezuelan seismological network.

Surface rupture of the Cariaco July 09, 1997 earthquake on the El Pilar fault, northeastern Venezuela

This paper discusses the surface rupture of the Cariaco July 09, 1997 Ms 6.8 earthquake in northeastern Venezuela – located at 10.545°N and 63.515°W and about 10 km deep. The field reconnaissance of the ground breaks confirms that this event took place on the ENE–WSW trending onshore portion of the dextral El Pilar fault (between the Gulfs of Cariaco and Paria), which is part of the major wrenching system within the Caribbean–South America plate boundary zone. Dextral slip along this fault was further supported by the structural style of this rupture (en echelon right-lateral R shears connected by mole tracks at restraining stepovers) and by larger geometric complexities (pop-ups at Las Manoas and Guarapiche), as well as by the focal mechanism solutions determined for the event by several authors. This 1997 surface ruptre comprised two distinct sections, from west to east: (a) a main very conspicuous, continuous, 30-km-long, rather straight, 075°N-trending alignment of en echelon surface breaks, with a rather constant, purely dextral coseismic slip of about 25 cm, but reaching a maximum value of 40 cm slightly northwest of Pantoño; and (b) a secondary discontinuous, 10-km-long, boomerang-shaped rupture, with a maximum coseismic slip of 20 cm at Guarapiche. The onshore extent of the surface rupture totalled 36 km, but may continue westward underwater, as suggested by the very shallow aftershock seismicity. This aftershock activity also clearly defined the steep north dip of the fault plane along the western rupture, suggesting tectonic inheritance on this major fault. From many locals' accounts, the rupture seems to have propagated from Pantoño to the west (highly asymmetric bidirectionality). This suggests that earthquake nucleation happened at or near the Casanay–Guarapiche restraining bend and rupture quickly propagated westward, allowing only a small fraction to progress eastwards beyond the bend. Additionally, the large fraction of after-slip (or creep) released is to be related to such restraining bend, which seems to have partly locked slip during rupture.

Quaternary tectonics and present stress tensor of the inverted northern Falcón Basin, northwestern Venezuela

The Tertiary Falcón Basin in northwestern Venezuela has a privileged position in the geodynamic puzzle of northwestern South America, occurring in a region where several major plates (Caribbean, South America and Nazca) and minor lithospheric blocks (Maracaibo, Bonaire and Western Colombia) are interacting. A combination of good exposures due to aridity and a near-continuous sedimentary record in a now inverted basin helps to unravel the Neogene and Quaternary geodynamic evolution of this region. A neotectonic and microtectonic investigation of the Plio-Quaternary sedimentary rocks of the northern Falcón Basin reveals that this region is subject to a compressive to transpressive regime at present. This regime is characterized by a NNW–SSE oriented maximum horizontal stress, and a ENE–WSW trending intermediate (or minimum) horizontal stress, as is confirmed by focal mechanism solutions. This stress field is in agreement both with the NNE-directed extrusion of the Maracaibo and Bonaire blocks in Western Venezuela, where the Falcón Basin is located, and present-day transpression along the Caribbean-South America plate boundary zone.

Historical seismicity of the southeastern Caribbean and tectonic implications

We have relocated the twenty-eight largest magnitude (4.3≤M s ≤7.3) historical (1922–1963) earthquakes of the southeastern Caribbean. We also present new focal mechanisms for seven of these events. The relocations are based on reported ISSP andS arrival times that we analyzed using generalized linear inversion techniques. The new focal mechanisms were constrained by first motionP polarities as reported by the ISS and as picked by us where records were available, and by the polarities and ratios ofSH andsSH, andSV andsSV arrivals that we determined from seismograms. The results of the relocations are commensurate with the distribution of seismicity observed in the recent era: hypocenters are shallow and intermediate in depth (0–200 km), and the events occur almost exclusively in areas known to be currently seismic. The frequent seismic activity in the vicinity of the Paria Peninsula, Venezuela, is clearly a persistent feature of the regional earthquake pattern; intermediate depth earthquakes indicative of subduction beneath the Caribbean plate occur here and along the Lesser Antilles arc. The Grenadines seismic gap is confirmed as an area of low seismic moment release throughout the historical era. Trinidad and the eastern Gulf of Paria were also largely quiescent. The new focal mechanisms, despite being a sparse data set, give significant insight into both subduction processes along the Lesser Antilles arc and into the shallow deformation of the Caribbean-South America plate boundary zone. The largest earthquake to have occurred in this region, the 19 March 1953 event (M m =7.01), is a Lesser Antilles slab deformation event, and another earthquake in this region of the Lesser Antilles is probably a rarely-observed interplate thrust event. Shallow deformation in the plate boundary zone is complex and, near the Paria Penninsula, involves mixed southeastward thrusting and dextral strike-slip on east-striking faults, and secondarily, normal faulting. Bending of the subducting Atlantic-South American plate also seems to generate seisms. The rather high ratio of intraplate deformation to interplate deformation observed along the Lesser Antilles subduction zone in the more recent era seems to have been operative in the historical era as well.

Caribbean Basin Framework, 4: Maracaibo Basin, Northwestern Venezuela

The Maracaibo basin is presently located in a topographic depression on the Maracaibo block, a triangular, fault-bounded block within the Caribbean-South America plate boundary of northwestern Venezuela. Intense oil exploration over the last 50 years has produced a large amount of seismic and well data that can be used to constrain four Jurassic to Recent tectonic and depositional events that affected the region: (1). Late Jurassic rift phase and subsidence along normal faults striking north-northeast across the floor of the basin; (2) Cretaceous to early Eocene subsidence recorded by shallow to deep marine carbonate and clastic rocks that thicken from south to north and completely cover Permian rocks of the Merida arch; (3) Eocene folding, thrusting, and initial reactivation of Jurassic normal faults as convergent strike-slip and reverse faults. Eocene clastic sediments are thickest in a narrow northwest-trending foredeep on the northeastern margin of the basin; (4) Late Miocene to Recent northwest-southeast convergence is marked by continued reactivation of Jurassic normal faults as reverse and left-lateral strike-slip faults, uplift of mountain ranges bordering the basin, and deposition of up to 10 km of clastic sediment.

Origin of Cariaco Basin, southern Caribbean Sea

The Cariaco basin, an anoxic basin in the central-eastern Venezuelan continental borderland, is located in the area of overlap of two en echelon right-lateral strike-slip fault zones, the Morón and El Pilar fault zones. On the basis of 28 acoustic reflection profiles across it, the basin is interpreted as a pull-apart basin due to east—west tension in the area of the right-step between the two fault zones (125 km of overlap and 35 km separation). The offset along the fault zones is less than 100 km, and at least 25 km. Its age is most probably Quaternary, as suggested by the thickness of the sedimentary fill and the estimated rate of deposition, and because strike-slip displacement along the master faults probably began no earlier than the Late Tertiary. The Cariaco basin is the largest pull-apart basin along the Boconó—Morón—El Pilar fault system which is a part of the Caribbean—South America plate boundary.