December 16

Benjamin A. Brooks Hawaii Institute of Geophysics and Planetology, University of Hawaii

Crustal Motion in the Southern Andes (26-36°S): Evidence for an Andean Microplate?

A new Global Positioning System (GPS)-derived velocity field for the Andes mountains (26°-36°S) allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen's opposing sides. Adding an 'Andes' microplate to the traditional description of Nazca-South America plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field. The results suggest the oceanic Nazca boundary is fully locked while the continental backarc boundary creeps continuously at ~4.5 mm/yr. The excellent fit of model to data (1.7mm/yr RMS velocity misfit), and the relative aseismicity of the upper crust in the interior Andean region in comparison with its boundaries, supports the notion that the mountains are currently not accruing significant permanent strains. Additionally, our analysis implies that permanent deformation is not accumulating throughout the backarc contractional wedge; instead, deformation is accommodated only within a narrow zone at the frontal portion of the wedge.