Seismological and petrological crustal structure in the southwest of the Sierra de Pie de Palo, San Juan (Argentina)

PERARNAU, MARCELO; CASTRO DE MACHUCA, BRIGIDA; ALVARADO, PATRICIA; LOPEZ, MARIA GIMENA; SAEZ, MAURO; GILBERT, HERSCH; LINKIMER, LEOPOLD

Foz de Iguazu

Encuentro; The Meeting of the Americas Supplement (Meet. Am. Suppl.); 2010

American Geophysical Union (AGU)

The Sierra the Pie de Palo is located near 31.5°S in the Andean backarck region where the Nazca plate is subducting beneath South America nearly horizontal to the northeast. This geometry of the subducted plate is potentially linked to the subduction of the Juan Fernandez Ridge about 100-km depth and plays an important role in absence of active volcanism, hydration of the upper mantle, and styles of deformation in the Andean backarc region. Previous studies have revealed unexpected variations in the seismic wave velocities of the upper mantle, possible overthickened continental crust with a complex structure that may include fault detachments and dense lower crust. In this presentation we show receiver function analyses in the southwest of the Sierra Pie de Palo which is the westernmost basement cored uplift of the active western Sierras Pampeanas. Our data consisted of good-quality P-wave teleseismic receiver functions recorded at the broadband station Coronel Fontana (CFAA) which is part of the CTBTO global network. We constrain depth, P-wave velocity and average P- to S-wave velocity ratio for the Moho, mid-crustal discontinuities and the slab. In addition, we have collected samples from the rocks in the nearby area. We combined this information to test petrological and seismic models. Our main results indicate a thick crust of 47-km depth including a potential decollement level at 16-km depth and a lower crust layer of higher seismic velocity and higher density compatible with granulite/ecoglite lithologies.