Project Summary

The interiors of the continents are constructed of island arcs and microcontinental fragments. Theories of continental formation rely on island arc accretion to continental margins as a primary element in post Archean continental development. The Caribbean South American plate boundary zone is the result of Caribbean American plate interactions starting in the Mesozoic which are now accreting the Leeward Antilles arc to the South American craton. This plate boundary and the processes associated with it have been active in near present form since the Eocene (~5OMa). The boundary now consists of trenches of opposite polarity at either end of a right lateral transpressional zone: The transpressional zone extends from the Gulf of Paria between Trinidad and Venezuela, to Colombia, connecting the NW dipping Lesser Antilles subduction zone in the east to the SE dipping Southern Caribbean Deformation Belt subduction zone in the west. Teleseismic tomography and seismicity patterns show the Caribbean plate overriding the Atlantic seafloor of the South American plate east of the Gulf of Paria. In the west the Caribbean plate is subducting beneath continental South America. The subduction polarity reversal and right lateral strike slip zone connecting the trenches developed following initial collision of the Great Caribbean arc with South America in mid- to Late Cretaceous time (~120Ma). The plate boundary now consists of a series of EW trending allochthonous belts which include the Leeward Antilles arc, the metamorphic belts of the Caribbean Mountain system, and the para autochthonous Serrania del Interior foreland fold and thrust belt. The Leeward Antilles arc has been diachronously colliding obliquely along this boundary since the Eocene, starting in western Venezuela and migrating eastward with the Caribbean plate relative to South America.

In addition to the eastward migrating Lesser Antilles trench and accreting Leeward Antilles island arc, the exhumation of the high pressure low temperature (HP/LT) metamorphic belts of the Caribbean Mountain system, the formation of the Serrania fold and thrust belt and associated foreland basins are all diachronous. All of these tectonic processes began occurring in the Eocene in the west and have continued moving eastward along the margin until the present.

The HP/LT rocks (up to 75km depth) formed in a subduction zone far to the west and are now at the surface in belts showing progressively younger HP/LT metamorphism from west to east. The ascent and exhumation of the metamorphic belts is the result of extension and compression which operate in concert with poorly understood mantle processes: arc parallel extension tectonically unroofs deeply buried rocks which are then obducted southward over the margin and eroded. The entire orogenic belt has developed above a crustal scale basal decollement into which both the thrust faults and the strike slip faults merge, making the entire plate boundary a zone of orogenic float that extends into the mantle beneath the plate boundary. This geometry provides a pathway for HP rocks subducted in the mantle to mechanically re enter the crust. The subduction polarity reversal permits the exhumation process, with the strike slip system and eastern subduction zone providing both the paths of uplift and the exhumation itself.

We proposed a geology and geophysics investigation to test hypotheses related to arc continent collision and accretion, HP/LT rock exhumation, and development of folded belts. Geophysical investigations of crust mantle structure will be combined with geologic studies of timing, deformation, and uplift. We propose to time the cessation of arc magmatism associated with arc accretion, and time and measure peak conditions of HP/LT metamorphism and exhumation across the length of the boundary. The geometries of arc accretion, exhumation, and the hinterland of the folded belt will be investigated with active and passive seismic methods. This plate boundary is ideal for cost effective land marine seismic investigations. The proposed research, undertaken by 9 PI's at 4 U.S. universities (see BOLIVAR people), will provide an understanding of the time transgressive history and crust mantle mechanical processes by which island arcs accrete to continents along oblique collision zones, deeply buried HP/LT rocks are exhumed, and fold and thrust belts form in transpressive environments. In the mantle we will examine how the subcrustal lithosphere drives the accretion of the arc and the exhumation of the metamorphic belts, how subduction polarity reverses, and we will determine the flow patterns of the sub lithospheric mantle beneath the plate boundary and around northern South America.

We have completed a very successful data acquisition effort, having conducted both active and passive land-marine seismic experiments, and numerous geologic/geochemical studies on the Venezuelan mainland and in the Leeward Antilles archipelago (Figures 1&2). We are now at an intermediate stage of primary data analysis, and in the very preliminary stages of data integration and synthesis. The reader should understand that our study area is approximately the size of California and its offshore continental margin, an area of more than 600,000 km2, and has an equally complicated Cenozoic tectonic history.

We have established a long-term research relationship with FUNVISIS2, the Venezuelan government seismological agency, and two leading Venezuelan universities3. Our most recent project workshop in Colonia Tovar, Ve., in October 2005, hosted more than 60 U.S. and Venezuelan scientists and students. In Venezuela BOLIVAR has a formal multi-year counterpart named GEODINOS4, fundedby FONACIT5, the Venezuelan science foundation, with additional funding from PDVSA6 and INTEVEP7. The GEODINOS principal investigators are Michael Schmitz, Herbert Rendón, Franck Audemard (FUNVISIS and Adjunct Professors, UCV), Franco Urbani (FUNVISIS and Professor, UCV), Inírida Rodríguez (Professor and Head of Department of Geophysics (UCV), MIguel Bosch, Ricardo Alezones and Laura Piñero (Professors,UCV), Wuilian Torres (Researcher, Centre of Digital Imaging Processing (CPDI/FII) and Maria Jácome and Carlos Izárra (Professors at Simon Bolivar University).

We also have developed a working relationship with the Netherland Antilles Meteorological Service (NAMS) in the ABC’s (Aruba, Bonaire, and Curaçao) who are operating two broadband seismograph stations owned by Rice. One of these has a direct internet connection provided by NAMS; the other will shortly. Recently we have also reached an agreement for data exchange with the Seismic Research Unit at the University of the West Indies in Trinidad-Tobago and recovered all of the broadband seismic data relevant to our project from their network (see http://www.uwiseismic.com/Earthquakes/eq_monitoring.html).

Supported by the NSF Continental Dynamics Program