@article {bezada_subduction_2010, title = {Subduction in the southern Caribbean: Images from finite-frequency P wave tomography}, journal = {Journal of Geophysical Research: Solid Earth}, volume = {115}, number = {B12}, year = {2010}, note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2010JB007682}, abstract = {The eastern boundary of the Caribbean plate is marked by subduction of the Atlantic under the Lesser Antilles. The southeastern plate boundary is characterized by a strike-slip margin, while different configurations of subduction of the southwest Caribbean under South America have been proposed. We investigate the slab geometry in the upper mantle using multiple-frequency, teleseismic P wave tomography. Waveforms from P and PKPdf phases from 285 (Mb > 5.0) events occurring at epicentral distances from 30{\textdegree} to 90{\textdegree} and greater than 150{\textdegree} were bandpass filtered and cross-correlated to obtain up to three sets of delay times for each event. The delay times were inverted using approximate first Fresnel zone sensitivity kernels. Our results show the subducting Atlantic slab, as well as a second slab in the west of the study area that we interpret as a subducting fragment of the Caribbean plate. Both slabs have steep dips where imaged and can be traced to depths greater than 600 km. These results are consistent with transition zone boundary topography as determined by receiver function analysis. The Atlantic slab extends continent-ward south of the plate bounding strike-slip margin. We interpret this extension as continental margin lithospheric mantle that is detaching from beneath South America and subducting along with the oceanic Atlantic slab. The steep subduction of the Caribbean occurs \~{}500 km landward from the trench, implying an initial stage of shallow subduction as far to the east as the Lake Maracaibo-M{\'e}rida Andes region, as has been inferred from intermediate depth seismicity.}, keywords = {P-wave tomography, southern Caribbean, subduction}, issn = {2156-2202}, doi = {10.1029/2010JB007682}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2010JB007682}, author = {Bezada, M. J. and Levander, A. and Schmandt, B.} } @article {clark_characterizing_2008, title = {Characterizing the Caribbean{\textendash}South American plate boundary at 64{\textdegree}W using wide-angle seismic data}, journal = {Journal of Geophysical Research: Solid Earth}, volume = {113}, number = {B7}, year = {2008}, note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2007JB005329}, abstract = {We present wide-angle velocity modeling results from profile 64{\textdegree}W of the Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region (BOLIVAR) project. Line 64W is a 460-km-long, approximately north-south, onshore-offshore reflection/refraction transect located approximately at 64{\textdegree}W longitude. The profile extends across the transform plate boundary between the southeastern Caribbean (CAR) and South American (SA) plates. East of the profile the plate boundary bends to the north, and SA subducts beneath CAR. We utilize first-arrival tomography to resolve a smooth velocity field for the sediments and upper/middle crust and then use a layered approach to resolve a sharp velocity contrast for the Moho, simultaneously inverting refracted Pn and reflected PmP arrivals. We image crustal and upper mantle structure across the plate boundary zone. We interpret that the strike-slip system that accommodates relative motion between CAR and SA extends near vertically through the entire crust and offsets the Moho. We see no evidence supporting a major component of convergence, and rather than a wide boundary zone of overlapping lithospheric plates, we interpret the plate boundary to be confined to the 33-km-wide, near-vertical strike-slip system. Previously interpreted thrust faults flanking the strike-slip system appear to be confined to the upper/middle crust and may be related to the detachment of subducting South American lithosphere at the southern terminus of the Lesser Antilles subduction zone east of 64{\textdegree}W.}, keywords = {El Pilar, velocity modeling, Venezuela margin}, issn = {2156-2202}, doi = {10.1029/2007JB005329}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2007JB005329}, author = {Clark, S. A. and Zelt, C. A. and Magnani, M. B. and Levander, A.} } @article {clark_identification_2008, title = {Identification and tectonic implications of a tear in the South American plate at the southern end of the Lesser Antilles}, journal = {Geochemistry, Geophysics, Geosystems}, volume = {9}, number = {11}, year = {2008}, note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2008GC002084}, abstract = {In the southeast corner of the Caribbean, westward subduction of (Atlantic) oceanic South America beneath the Lesser Antilles transitions to east-west transform motion between continental South America and the Caribbean plate. This geometry requires negatively buoyant, subducting, oceanic South American lithosphere to progressively detach from positively buoyant, continental South American lithosphere. The most widely accepted model is slab break-off, with oblique arc-continent collision and northwest dipping, continental subduction precipitating narrow rifting in the subducting slab. In contrast, the subduction-transform edge propagator (STEP) model conceptualizes progressive detachment along a vertical, dip-slip tear through the lithosphere, with stress focused at the edge of the propagating transform boundary. We present four types of seismic data to resolve the ongoing lithospheric detachment: local seismicity, receiver functions, wide-angle seismic velocity inversion, and a regional, balanced cross section constrained by petroleum industry data. These four data sets image a near-vertical tear extending through the entire lithosphere, revealing a key mechanism for the structural evolution of Venezuela.}, keywords = {jelly sandwich, lithospheric detachment, mantle dynamics, slab break-off, STEP, tear}, issn = {1525-2027}, doi = {10.1029/2008GC002084}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2008GC002084}, author = {Clark, S. A. and Sobiesiak, M. and Zelt, C. A. and Magnani, M. B. and Miller, M. S. and Bezada, M. J. and Levander, A.} } @article {clark_negligible_2008, title = {Negligible convergence and lithospheric tearing along the Caribbean{\textendash}South American plate boundary at 64{\textdegree}W}, journal = {Tectonics}, volume = {27}, number = {6}, year = {2008}, note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2008TC002328}, abstract = {Prior studies of the Caribbean{\textendash}South American plate boundary have suffered from poor constraint on the structure of the crust and uppermost mantle. We use a recent wide-angle velocity model from the Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region project to constrain new seismic reflection data and previously published line drawing interpretations of the Caribbean{\textendash}South American plate boundary at 64{\textdegree}W. Though commonly characterized as obliquely convergent, we determine that convergence is negligible in our study area. Previous estimates of Miocene to present north-south shortening onshore eastern Venezuela have commonly been 115 km or higher, but we constrain shortening to \~{}35 km onshore, with an additional \~{}30 km offshore. With such minor convergence, we conclude that uplift and basin subsidence in eastern Venezuela does not derive from typical collisional orogeny. Instead, the largely vertical tectonics likely result from mantle dynamics associated with an eastward propagating, near-vertical tear in the lithosphere along the former passive margin.}, keywords = {El Pilar fault, Serrania del Interior, STEP fault}, issn = {1944-9194}, doi = {10.1029/2008TC002328}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2008TC002328}, author = {Clark, S. A. and Levander, A. and Magnani, M. B. and Zelt, C. A.} }