SEISMIC STRUCTURE OF THE LEEWARD ANTILLES ARC AND GROWTH OF THE SOUTH AMERICAN CONTINENT

We invert traveltimes from sparse 3-D wide angle seismic data acquired across the Leeward Antilles arc for crustal velocities and Moho depth. We provide evidence for a possible means of continental crust growth by the accretion of the Leeward Antilles arc to South America. One of the most accepted theories for continental crustal growth is the accretion of island arcs to form continental masses in the Archean and Paleo-Proterozoic. This process led to the stabilization of the continents with thick, bouyant mantle beneath the Archean cores. One argument against modern island arc accretion as a means of continental growth is the difference in composition between continental crust and normal island arc crust. The average continental crust is known to be intermediate in composition while normal island arc crusts have been shown, from seismic data, to be mafic. The Caribbean-South American plate boundary is an oblique transpressional zone where the Leeward Antilles arc appears to be accreting onto the South American continent. Our results suggest that the arc has a bulk intermediate composition.