Aseismic continuation of the Lesser Antilles slab beneath continental South America

Abstract

We present results of travel time inversions of teleseismic P and S waves recorded at the SECaSA92 (Southeast Caribbean South America 1992) temporary broadband array in northeastern Venezuela and Trinidad. The inversions reveal the unusual structure of the southern termination of the Lesser Antilles subduction zone: A minimum 2% relatively high‐velocity anomaly trends WSW from the seismically defined Lesser Antilles slab beneath and NW of the Paria Peninsula to a point below the Venezuelan Serranía del Interior, well south of the Caribbean coast. Resolution tests utilizing actual ray geometries and densities of the source data indicate that the regional‐scale structure beneath the study area is reasonably well resolved. Thus a detached and detaching subducted South American slab appears to lie beneath continental South America. We infer that oceanic South American lithosphere has been overridden to a significant degree by continental South America. The detached slab now lying beneath continental South America was driven into its current position after detaching from the former eastward striking Mesozoic ocean‐continent passive margin as this margin entered the subduction zone. Because oceanic and continental South America are still attached without apparent relative motion between them along the Atlantic passive margin southeast of our study region, the slab must be the actively moving element during continental overriding. Thus the slab and its surrounding mantle (both Caribbean and South America) beneath northeastern South America are mobile and have moved ESE relative to the stable Guyana Shield craton.

Constraints on mantle flow at the Caribbean–South American plate boundary inferred from shear wave splitting

“…[6] The Maracaibo and western Venezuela regions are most likely influenced by the paleo-Ca and Nazca plates' subductions dipping east beneath the Maracaibo block and northwest SA, respectively [Van der Hilst and Mann, 1994;Taboada et al, 2000;Bosch, 1997;Bezada et al, 2008]. The geometry of subduction in this tectonic corner is far from clear.…”

“…The BOLIVAR project deployed stations in the same region studied by Russo et al [1996] but extending over a much larger portion of the plate boundary ( Figure 1). We combine the BOLIVAR data with measurements from Russo et al [1996] to test several working hypotheses that have been posed to explain Caribbean tectonics: (1) Caribbean underthrusting of SA [Pindell et al, 1988], (2) independent motion of the Maracaibo block [Audemard and Audemard, 2002], and (3) Lesser Antilles Arc subduction as either a hinge geometry [Govers and Wortel, 2005;Molnar and Sykes, 1969] or tensile tear geometry [Clark et al, 2008;VanDecar et al, 2003]. In addition, these data provide some of the first measurements that can be used to investigate whether mantle flow changes as the setting changes from a subduction and transpressional zone [Weber et al, 2001] into a stable craton with a possible continental keel mantle geometry.…”

Crustal structure of the South American–Caribbean plate boundary at 67°W from controlled source seismic data

“…While the plate-scale architecture of the boundary has been defined by regional tomography studies (>100 km in depth) [Van der Hilst, 1990;VanDecar et al, 2003], the connection between the mantle features and the uppermost crust has been hampered by the lack of lithospheric-scale data.…”

New Bouguer Gravity Maps of Venezuela: Representation and Analysis of Free-Air and Bouguer Anomalies with Emphasis on Spectral Analyses and Elastic Thickness

“…This pronounced negative Bouguer gravity anomaly has been studied by several authors [3,[51][52][53][54]. The negative gravity anomaly is roughly parallel to the arc platform extension, but it does not extend west of Gulf of Paria.…”