Geometry and State of Stress of the Slab Beneath the North Central Andes

A. Kumar and L. S. Wagner
Geological Sciences, University of North Carolina at Chapel Hill

The central Andean plateau of southern Peru and Bolivia is one of the highest topographic features on the Earth. It has strongly influenced the local and regional climate since the early Miocene by affecting the regional atmospheric dynamics that control circulation and precipitation. Our understanding of the surface and subsurface processes responsible for the plateau formation and evolution are still unclear. There are two end member models proposed for this uplift: (1) Slow and steady rise since the late Eocene (~40 Ma) with maximum upper crustal shortening between 30 and 10 Ma or (2) rapid surface uplift of ~2.5 km in the late Miocene between 10.3 and 6.7 Ma. The rapid uplift theory argues for the wholesale removal of a thick portion of the lower eclogitic crust and upper mantle lithosphere. A slow and steady uplift of Andes suggests continuous removal of lower lithosphere, proportional to the rate of shortening. I am presenting the earthquake locations and focal mechanisms using data from the network of 90 broadband seismic stations. The new earthquake locations provide improved insight about the geometry of Nazca slab and also put an upper bound on the thickness of overriding lithosphere. These data shed new light on the geodynamic effect of the corner flow on lithospheric delamination or ablative subduction process. Focal mechanisms of crustal events provide insight into the character of the upper crust and assist in identifying the location of ongoing deformation in the central Andes. Results of the focal mechanism analyses of the slab events are helpful in improving our understanding of the stress state of the Nazca slab.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013