P-wave Velocity Structure beneath South America from Multi-frequency Tomography

Abstract:

We present a P-wave tomography model of mantle structure beneath South America, down to ~1800 km depth. DETOX-P1 is a global-scale, multi-frequency inversion of teleseismic P-waves with a particular focus on data sets from South America, where vast areas are sparsely instrumented. We measured ~717k cross-correlation traveltimes on 529 broadband stations in South America and on 6,953 receivers elsewhere, and closed coverage gaps by adding analyst-picked travel times from the International Seismological Centre. By their locations, depths, and geometries, we distinguish four high-velocity provinces under South America, interpreted as subducted lithosphere ('slabs'). The deepest (~1800-1200 km depth) and shallowest (< 600 km) slab provinces are observed under the North Andean Western Cordillera near the continent's west coast. At intermediate depths (~1200-900 km, ~900-600 km), two slab provinces are observed farther east, under Brazil, Bolivia and Venezuela, with links to the Caribbean. Above ~1000 km, slabs are paralleled and underlain on their oceanward flanks by a belt of seismically slow mantle. We interpret the slabs relative to South America's paleo-position over time, assuming that slabs sank essentially vertically (no more than a few hundred kilometers of lateral displacement). The shallowest slab province carries the geometric imprint of the continental margin and represents ocean-beneath-continent subduction during Cenozoic times. The deepest, far-westerly slab complex formed under intra-oceanic trenches during Late Jurassic and Early Cretaceous times, far west of South America's paleo-position adjoined to Africa. The two intermediate slab complexes record the gradual transition from intra-oceanic subduction to Cenozoic "Andean-style" subduction.