Distribution and Rates of Quaternary Deformation within the Pampean Flat Slab Segment of the Central Andes of Argentina from 30-32°S

The Pampean Flat Slab is characterized by a wide zone of active upper-plate deformation that involves both thin- and thick-skinned deformation. It provides a rare opportunity to explore the possible control of slab geometry, deformation style, and tectonic evolution of structures on upper-plate strain distribution; observe the distribution and relative proportions of shortening accommodated by Quaternary plate-boundary related and intraplate contractional deformation; compare the potential of these faults for generating devastating (≥ Mw 7) earthquakes; and apply geomorphic indices to analyze regional strain distribution patterns. This thesis provides valuable constraints on regional strain distribution for the Pampean Flat Slab since at least the Pleistocene, from both absolute and relative geomorphic slip rates. A shortening rate of ~0.4 mm/yr since Mid-Pleistocene was measured on the La Rinconada Fault Zone (LRFZ), which together with similarly low published slip rates on other regional faults is explained through nearly uniformly distributed strain in the predominantly thin-skinned Precordillera region. The LRFZ’s slip rate is associated with earthquake magnitudes of MW 6.6–7.2. In contrast, the much lower average shortening rate of ~0.2 mm/yr since the Mid-Pleistocene on the thick-skinned Las Chacras Fault Zone (LCFZ), located to the east of the LRFZ, suggests a possible W-E trend of decreasing shortening rates in the Pampean flat slab. Earthquake magnitudes of MW 6.7–7.1 estimated on the LCFZ shows that intraplate faults are equally capable of causing potentially devastating earthquakes. Relative slip rates from geomorphic indices exhibit a trend of W-E decreasing slip rates similar to that observed both in geodetic and neotectonic studies, indicating a possibly constant stress-field since at least the Pleistocene. This spatial correspondence in lowering of slip rates with the resumption of a more steeply subducting Nazca plate points to the first documented change in slip rates as a function of slab dip in the Pampean Flat Slab. Relative slip rates also pointed to sites requiring further detailed studies. Knowledge of the controls on active upper plate deformation in the Pampean Flat Slab segment therefore provides additional information for better understanding of the behavior and evolution of present-day and ancient flat slab settings worldwide.Ph.D