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.
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We are thankful for the contribution of volunteers, other field personnel from various US and Venezuelan universities and institutions (FUNVISIS, USB, UCV, PDVSA, DHN, Rice University), as well staff of IRIS-PASSCAL Instrument Centre (M. Fort, B. Greschke, E. Gutierrez, P. Miller, W. Zamora), and the crews from the research vessels R/V Maurice Ewing and R/V Seward Johnson II, for the realization of the seismic measurements. We thank the local communities and land owners for the support and permit for installation of recording equipment and drilling and blasting of land shots. We acknowledge the contributions of G. Housepian (Geointer) and L. Pregitzer (CAVIM) and their respective crews for drilling and blasting, respectively. Recording instruments at land were provided by IRIS Instrument Centre, New Mexico, which is gratefully acknowledged. We thank J.E. Soares and E. Flüh for detailed reviews, which helped to improve considerably the quality of the paper. Further members of the BOLIVAR active seismic working group are: D. Sawyer, (Rice); V. Rocabado, J. Sánchez (FUNVISIS); G. Christeson, P. Mann, A. Escalona (UTIG); N. Nevado (PDVSA-INTEVEP). Contribution to projects FONACIT G-2002000478, PDVSA-INTEVEP — FUNVISIS — 04–141, and NSF — Continental Dynamics Program grant EAR-003572.
- Crustal thickness
- Deep seismic observations
- South America