Deformation and rheology of the Central Andean lithosphere

FEDERICO IBARRA; CLAUDIA PREZZI; MARÍA LAURA GÓMEZ DACAL; MAGDALENA SCHECK-WENDEROTH; BOTT, JUDITH; MANFRED STRECKER

Congreso; 25 Latin American Colloquium of Geosciences; 2019

Deformation processes in the Central Andes are complex and heterogeneous. The location and style of deformation in the orogenic front change along strike. North of 22°S, a thin-skinned fold and thrust belt (Subandean Ranges) progressively propagates to the east through a décollement detached in Paleozoic units; whereas south of 22°S, thick-skinned systems (Santa Barbara System, Pampean Ranges) irregularly deform the foreland. Previous studies have investigated the controlling factors on such heterogeneity; however, most of them have focused either on the uppermost crust (i.e. sediments and inherited structures) or the nature of the subduction zone. In this contribution we analyze the link between the observed deformation and the physical state of the lithosphere. We have previously published a 3D data-constrained density model of the region validated through forward modeling of the Bouguer anomaly. Based on this model and published values of thermal conductivity and radiogenic heat production for different rock types, we calculated the conductive thermal field for steady-state conditions. Subsequently, using the obtained temperatures and published mechanical properties of rocks, we calculated the maximum differential stress for brittle (Byerlees law) and ductile (dislocation creep and dislocation glide) behaviors at each X-Y-Z position. Finally, we constructed yield strength envelopes (YSE) and maps of integrated strength. Interestingly, our results show a correlation between the observed deformation and the strength of the lithosphere. Most seismic events and active faults are clustered in the transition between domains of weak and strong lithosphere.