Abstract We discuss results from a large-scale investigation of the southeastern Caribbean (CAR) plate boundary conducted in Venezuela and the Leeward Antilles by Venezuelan and U.S. scientists. The project, known as BOLIVAR in the U.S. and GEODINOS in Venezuela, included offshore reflection, onshore-offshore wide-angle reflection/refraction profiling, teleseismic body and surface wave tomography, structural geology, and geochemistry. The various types of seismic imaging of the crust and upper mantle in northern South America provide a number of important constraints on the evolution of the Caribbean-South American plate boundary, and identify substantial modifications to crust and upper mantle structure of coastal South America resulting from plate boundary tectonics. As the Atlantic subducts, the southern end of the descending slab applies a load to the adjacent South American lithosphere, depressing the South American lithosphere and providing space for the leading edge of the Caribbean to overthrust northern South America. This has a number of consequences that extend from the surface to the base of the lithosphere: (1) As suggested by others, the descending Atlantic tears from the SA continental margin, producing an isolated nest of intermediate depth earthquakes. This lithospheric tear is associated with, but offset from the eastern end of the South American-Caribbean strike-slip fault boundary. (2) Lithospheric flexure at the South American coast creates space to accommodate overthrusting of South American passive margin deposits and Caribbean island arc and prism terranes, aiding in development of the coastal mountain belts and exhuming HP-LT rocks. (3) Flexure and overthrusting deepens the South American Moho to ~50 km in northeastern Venezuela, and over thrust terranes occupy the upper 25-50% of this thickness. (4) The depressed South American Moho is substantially offset (~15-20 km deeper) from that of the adjacent Antilles arc terranes. (5) Lastly, the subducting Atlantic plate viscously removes the base of the South American passive margin continental lithospheric mantle at least 100 kilometers south of the plate boundary and destabilizes the continental lithosphere farther inland, triggering convective instabilities in the lithosphere south of the plate boundary. Once subduction has migrated eastward from a given point along the margin, the load caused initially by Atlantic subduction is removed, allowing the crust to rebound, shallowing the South American Moho, reducing the Moho offset between coastal South America and the offshore terranes, and enhancing erosion of accreted terranes. We observe that the continental lithosphere west of the subduction zone is thinner than expected between the Guayana shield and the plate boundary. We hypothesize that the subducting Atlantic has viscously removed the mantle lithosphere beneath the South American continental margin and destabilized the lithosphere farther inland, everywhere west of the current subduction zone. Although modulated by the paleogeography of South America and preexisting lithospheric structures on both the South America and Caribbean plates, this simple time transgressive model of subduction, lithospheric loading, flexure, and viscous removal of mantle lithosphere can account for much of the lithospheric structure of northern South America as far west as the Boconó Fault. Development of the Boconó and Santa Marta-Bucaramanga faults has added an additional layer of tectonic complexity in western Venezuela in the past ~10-20 m.y. that overprints, but does not completely destroy, the effects of the migrating Atlantic subduction zone.

Abstract Eastern Venezuelan basin (EVB) is located in the northern South America, in the easternmost part of Venezuela, and it has been filling from the southwest by the Orinoco River since late Miocene – early Pliocene (?), forming the 12-km- thick Orinoco Delta in the Atlantic Ocean. To improve our understanding of the paleogeography and hydrocarbon potential of the eastern Venezuelan basin and the adjacent, thickly-buried segment of the South American passive margin, we use 620 km2 of 3D seismic, 650 km of 2D seismic, and five wells with well logs from the Punta Pescador area of northeastern Venezuela near the Columbus Channel and the border with Trinidad. The following sequence of Cenozoic events affecting the passive margin are proposed: (1) during the Oligocene and early Miocene, south to north flowing fluvial systems and associated deltas progradated northward from the Guyana shield; (2) the late Miocene Messinian event lowered eustatic sea level along the passive margin and produced a major erosional event that breached a continental high which allowed the Orinoco Delta to prograde rapidly into the deeper water Atlantic area in the earliest Pliocene; and (3) early Pliocene to recent progradation of the Orinoco Delta is well documented into the deeper water areas of Trinidad and offshore Venezuela. The onset of major input of the Orinoco River in this area is thought by most workers to be late Miocene in age, which is supported by a change in the flow direction interpreted in the seismic data, from south-north in the pre-late Miocene–early Pliocene section to southwest to northeast direction in the Pliocene to Recent sequence. Through the Cenozoic time, a superposition of fluvial system over deltaic and deep water facies evidences the progradation of the facies and the filling of the basin.

The prime cause of the relocation of one of the first villages founded in Venezuela by Spaniards in the early seventeenth century was likely motivated by earthquakes. San Antonio de Mucuñó, located in the Merida Andes ~200 km south-southeast of Maracaibo, was subjected to the effects of landslides triggered by a series of seismic events that took place in and around the year 1674. Historical documents, the geological and seismo-tectonic setting, and paleoseismic data support the conclusion that the earthquakes of 1674 occurred on the nearby, seismically active Bocono fault.

This work sheds light on one of the most important earthquakes in Venezuelan history. At 16:07 on Holy Thursday, 26 March 1812, Caracas and the surrounding province of Venezuela suffered a very destructive earthquake. The earthquake occurred at a time of great political, economic, and social upheaval, with the beginning of the republican revolution and the Spanish royalist military response. Within this historical context of conflict, documentary information may be biased and subjective. This chapter is a methodological and epistemological analysis of the 1812 earthquake damage from letters and manuscripts and an interpretation of the social impact of the earthquake within ideological, subjective, and political context. The widespread destruction of the city of Caracas was heterogeneous in its distribution. Damage was determined largely by the differences in the construction style and quality and by the maintenance status of the building. Based on analyses of three funeral books from the era, the number of earthquake victims in Caracas in 1812 may have been close to 2000. This value is lower than regional estimates of the death toll.

The Paria Península in eastern Venezuela exposes an E-W–oriented mountain belt composed of deformed and metamorphosed sediments that were deposited on the northern South American passive margin in early Mesozoic time. The metamorphic grade, mostly greenschist facies, decreases from north to south in a direction perpendicular to the trend of the metamorphic belt. Foliation (S 1 ) dips steeply to the south along the southern coast and progressively gentler to the north to 25–30°. S 1 strikes ∼ 060–075° subparallel to oblique to the general trend of the metamorphic belts. Stretching lineation (L 1 ) plunges variably to the SW. The pattern of crystallographic preferred orientation (CPO) of quartz c -axes indicates a transition from symmetric coaxial strain to weak top-to-SW or oblique-normal sense of shear. The fabric patterns suggest activation of the basal <a>, prism <a>, and rhomb <a> slip systems under relative low-temperature (300–400 °C). Apatite fission-track ages range from 29 Ma in the south to 5 Ma in the north. Similarly, samples in the northern and central zone yielded the youngest zircon fission track (FT) ages, ranging from 5 Ma to 9 Ma, and the southern zone yielded slightly older ages ca. 13 Ma. From the FT ages we estimate a diachronous cooling from south to north and a cooling rate in the range of 16–56 °C/m.y. (∼1–2 mm/yr of exhumation). That many of the cooling ages postdate pre–10 Ma transpression suggests that tectonically driven vertical extrusion alone cannot account for the observed exhumation. The topography of the Paria Península and its current precipitation pattern are both asymmetric. Exhumation, deformation, topography, erosion, and precipitation patterns from the transpressional orogen of the Paria Península are comparable to those described in the Southern Alps of New Zealand. A general model for these two-sided transpressional wedges is proposed based on geologic observations. Obliquity of the compression and erosion seems to play an important role in the evolution, exhumation, and deformation of these two naturally deformed orogens.