Arclogite nature of the Colombian Andes magmatic arc root: A receiver-function approach

Abstract

Arclogites are an important part of the continental arc root architecture. When overlooked, the crustal structure could be misinterpreted, assuming that the seismically defined Moho necessarily coincides with the crust-mantle boundary. Evaluating the possible presence of lower crustal rocks below the seismic Moho with physical properties resembling those of the underlying mantle, is therefore, of major importance. Through a multi-approach receiver function assessment, which includes shear wave velocity inversion, and determination of plausible crustal seismic velocity distributions from forward modeling, we present new constraints on the seismic structure of the arc root beneath the Colombian Andes magmatic arc. Results suggest a high-velocity arc root with a latitudinally variable thickness, from 13.5 to 20 km. The arc root is composed of a 4 to 6 km thick upper domain with seismic wave speeds 5% slower, and 8.5 to 14 km thick lower domain 5% faster, relative to the underlying uppermost mantle. This lower crustal structure, coupled with documented garnet pyroxenitic xenoliths, supports an arclogite nature for the Colombian Andes arc root.