Browsing by Author "Collo, Gilda"

The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of N-S reverse faults that disrupted a W-E Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., similar to 9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at similar to 477-470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the K-Ar dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 degrees C). K-Ar ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (similar to 360-220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of similar to 360 Ma and a last clay minerals forming event at similar to 220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (similar to 360-311 Ma for 2-1 mu m grain size fraction, similar to 326-286 Ma for 1-0.2 mu m and similar to 291-219 Ma of <0.2 mu m), we modeled discrete deformation events at similar to 417 Ma (ending of the Famatinian cycle), similar to 317-326 Ma (end of Gondwanic orogeny), and similar to 194-279 Ma (Early Permian - Jurassic deformation). According to our data, the Neogene reactivation would not have affected the K-Ar system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data. (C) 2015 Elsevier Ltd. All rights reserved.