Synorogenic Record of Basin Reorganization in the Sierras Pampeanas, La Rioja, Argentina

Tuesday, 16 December 2014
Andrea Stevens and Barbara Carrapa, University of Arizona, Tucson, AZ, United States
The Sierras Pampeanas of Argentina are characterized by surface exposures of Precambrian basement blocks. These uplifts segment the modern Andean foreland basin. This study uses the synorogenic sedimentary record to determine the timing of basin reorganization in the northwest Sierras Pampeanas tectonic province. Results shown here will test if basin reorganization coincides with the hypothesized onset of flat slab subduction determined using independent data sets. Specifically, this study focuses on the Los Colorados Range near Vinchina, La Rioja, Argentina (~ 28 ̊S). Here, we apply new geochronological constraints using U-Pb geochronology on zircons in intercalated ash layers to provide age control on a >10 km synorogenic section. We couple this age control with changes in paleoflow direction determined from provenance analysis on detrital cobbles and paleocurrent indicators. An abrupt change from thick channelized fluvial deposits to thin paleosol horizons requires a major change in the regional environment. We hypothesize that this basin reorganization is the result of basement block uplifts driven by the onset of flat slab subduction in the Miocene. The Sierras Pampeanas are an important natural laboratory for studying the interaction between slab orientation and surface geology. Here, the onset of modern flat slab subduction occurs shortly before a change in basin organization which is preserved in the sedimentary record. This link is important in interpreting the geological history of areas where the slab orientation is no longer preserved.