ABSTRACT The subduction-to-strike-slip transition (SSST) zone of the southeastern Caribbean is one of the thirty identified locations where active subduction and strike-slip tectonic styles transition along strongly curved and seismogenic plate boundaries. We use approximately 10,000 km (6000 mi) of 2-D seismic reflection, well, seismic tomographic, gravity, magnetic, earthquake focal mechanisms, and global positioning system (GPS) data to study the primary structures within the SSST zone. We analyze transitions of subducted slabs, basement areas, sedimentary basins, faults, and other structures from an area of westward-directed subduction of Atlantic oceanic crust beneath the Lesser Antilles arc, to a region of east–west-striking, right-lateral strike-slip faulting along the northern South American margin. Tectonic processes in the arcuate plate boundary zone include (1) oblique collision between the arcuate front of the Caribbean plate and the northern South American margin; (2) propagation of the Subduction-Transform Edge Propagator (STEP) fault as defined by Govers and Wortel (2005) ; and (3) north-to-northwest flexure of transitional South American lithosphere as the slab detaches from the South American continent, tears apart from the west-dipping segment of the slab to the north, and sinks into the mantle beneath the Caribbean plate. Northwest–southeast-oriented Atlantic oceanic fracture zones, and lithospheric transitional boundaries are a significant control on the evolution of the margin including the location and orientations of STEP faults, slab rollback, detachment, and tearing. Lithospheric deformation associated with STEP tearing and slab detachment influences the position, orientation, and evolution of crustal plate boundary structures and sedimentary basins discussed in more detail in Chapter 5 ( Alvarez et al., 2021 ). Sedimentary basins and structures of the southeastern Caribbean SSST zone are characterized by spatially and temporally complex uplift and subsidence patterns at the surface, which are the result of the multiphase deformational history that includes oblique collision, STEP faulting, and subducted slab dynamics, which are inherent to the bounding tectonic configuration.

Abstract On the eastern margin of the Panama Basin, the Nazca oceanic plate converges towards the continental plate of South America at approximately 53 mm a −1 . Subduction processes are accompanied by the presence of anomalous bathymetric elements including the Sandra Ridge. This east–west-orientated ridge is catalogued as an aborted rift derived from a magmatic spreading axis that was active between 12 and 9 Ma. Seismic activity within this structure is considered evidence of fault reactivation and tectonism. Once the structure reached the subduction trench several submarine landslides were triggered. Run-out lengths of these submarine landslides are perpendicular to the convergence of the structure with some units spreading and forming a wide fan that reaches tens of kilometres to the north and south of the trench. The area affected by the three main landslides varies between 130 and 300 km 2 approximately, with relatively superficial earthquakes (<33 km) and with magnitudes that reach up to M w 7.2. The morphology of the landslides suggests a retrogressive nature with younger events proximal to shore. This paper presents estimates of the age of these landslides and discusses sources of uncertainty regarding these times of occurrence.

Abstract We have estimated the Curie point depth (CPD) in the northwestern corner of South America and the southwestern Caribbean Sea from spectral analysis of magnetic anomalies extracted from the World Digital Magnetic Anomaly Map. To do this, we performed three different spectral methods and chose the model that best fits the geologic and geophysical characteristics of the study area. Then, we calculated the geothermal gradient from these CPD values to assess the likelihood of the hydrocarbon “Golden zone” being present in some of Colombia’s sedimentary basins. Similarly, we tried to establish empirical relationships between CPD, geothermal gradient, and heat flux. Our results show that the CPD lies between 12.6 km (7.8 mi) and 74 km (45.9 mi). The shallowest depths (<25 km [<15.5 mi]) are in the offshore Venezuela and Colombia basins of the Caribbean Sea, the onshore eastern Llanos and Caguan–Putumayo Basins, and southwestern Venezuela. The greatest depths (>50 km [>31 mi]) occur in parts of the western and central Cordilleras, Santander massif, and middle Magdalena, Catatumbo, Barinas-Apure, and Vaupes-Amazonas Basins. Based on the results, we found a relationship between an unexpected zone of deep CPD values (40–47 km [24.8–29.2 mi]) in the Colombia Basin and the presumable presence of an abnormal thick Caribbean Plateau with a continental inheritance. On the other hand, the contrasting deep and shallow CPD values in the Caribbean support the interpretation of flat subduction of the Caribbean plate beneath South America with a flexural topographic bulge toward the Sinu−San Jacinto and lower Magdalena Basins. Partial erosion of this bulge could have resulted in shallowing of the CPD with a consequent increase in geothermal gradient and heat flux. Also, we found a CPD shallowing beneath Caguan–Putumayo and eastern Llanos Basins. Finally, based on the calculated geothermal gradient values in Colombia, we consider that the Golden zone of hydrocarbon occurrence most likely exists in the Choco–Uraba, eastern Cordillera, Guajira−Los Cayos, eastern Llanos, and lower Magdalena Basins, while the Golden zone would be absent only in the Vaupes–Amazonas Basin.

Abstract Earthquake hypocenter relocations, earthquake focal mechanisms, P-wave velocity anomaly tomography, interpretation of deep-penetration seismic reflection lines, and gravity modeling are integrated to define an ESE, 110°-dipping zone of shallow subduction beneath northwestern Colombia. These data define a 15- to 16-km-thick (9.3–9.9 mi), late Cretaceous oceanic plateau (Caribbean plate) that is actively subducting with anomalous low Benioff zone seismicity at a dip of 3–8° over a down-dip distance of 200 km (124 mi) beneath a deformed sedimentary wedge (South Caribbean deformed belt). At a down-dip distance of 450 km (280 mi) from the frontal thrust of the accretionary wedge and at a depth of 130 km (81 mi), tomographic data show that the largely aseismic, subducting Caribbean plate bends and steepens to a dip of 28°–50°. In the depth range of 80–130 km (50–81 mi), tomographic data show that the subducted Caribbean slab exhibits a low-velocity anomaly that we interpret as evidence for slab delamination and enhanced dehydration by rising asthenosphere. Tomographic data beneath the middle Magdalena Basin of northern Colombia show a thick, cold continental lithosphere (ca 60–100 km [37–62 mi]) while gravity data beneath the lower Magdalena Basin show a thin continental crust (24–27 km [15–17 mi] thick) beneath which the Caribbean slab dips in the range of 40–50°. Minor subduction-related volcanism is present in the eastern Cordillera likely as a result of shallow subduction limiting the size of the mantle wedge that is needed for slab melting and arc-related volcanism. Understanding the subduction setting of northern Colombia is fundamental for understanding its heat flow, tectonic history, controls on subsidence, and other parameters needed for petroleum exploration both onshore and offshore.

Abstract We have analyzed a catalog compiled by the USGS for the period 1977–2014 of approximately 33.1 seismic events ( M w ≥ 3.0) and 2.3 focal mechanisms ( M w ≥ 4.9) located in the Caribbean plate, with depths ranging between 0 km and 200 km (124.2 mi). Data allowed calculation of the spatial variations of the seismic regime (the b -values based on the Gutenberg–Richter power law, and the fractal dimension or D -parameter) and the seismotectonic deformation rates. We find a strong depth dependence of the b -values and the D -parameter as well as a depth interval (40–80 m [24.8–49.7 mi]) with large mean deformation rates (2.0±0.49 cm/yr) that has been associated with the subduction process along the Caribbean plate. Finally, we suggest that the southern border of the Caribbean plate starts near the central segment of the Nazca Cocos Spreading Center (3.5°N–83°W); trends eastward along the Sandra ridge, the Caldas Tear; and then follows the eastern foothills of the northern Andes.