The Structural and Tectonic Evolution of the Arizaro Basin of the Puna Plateau in NW Argentina
Abstract
The Arizaro basin is the largest basin preserved within the Puna Plateau of NW Argentina; it contains ca. 5km of Eocene-Pliocene sedimentary strata of which more than 3km are Miocene fluvial-lacustrine deposits. Previous thermochronologic and sedimentological work document that the deformation front was within the Plateau in the Eocene whereas it was within the Eastern Cordillera at the time the thickest sedimentary sequence was deposited in the Arizaro basin; therefore, the basin could be considered as intermontane. However, other processes such as the loss of mantle lithosphere and lower crust have been proposed as the cause of magmatic activity and surface uplift in the late Cenozoic, which is well documented through geophysical evidence. This opens the possibility for other basin mechanisms to contribute to basin accommodation space and deformation. Backarc extension has also been proposed. Here we present a multi-disciplinary study that addresses the contribution of two end-member mechanisms of basin formation: 1) loading and flexure within an intermontane setting; and 2) subsidence due to small scale lithospheric foundering beneath the basin. In the first case, out-of-sequence deformation and reactivation of basin bounding structures are predicted. In the latter case, radially oriented subsidence and shortening would occur during the lithospheric removal, followed by extension and basin incision. The Arizaro basin is uniquely suited to test these hypotheses because of both its location, overlying the thinnest area of the crust and lithosphere within the Plateau, and the presence of the thickest late Cenozoic section. Preliminary data was collected across the eastern side of the Salar to determine the structural style and overall pattern of deformation. Fifteen new samples were collected for low-T thermochronology and geochronology to establish the timing of tectono-thermal events in the region via apatite fission track and zircon U-Pb geochronology. Structural data from more than 300 stations within the 30km x 27km mapped area show no evidence of reactivated or young normal faulting, suggesting that the back-arc scenario is unlikely. Both thin- and thick-skinned structures were observed. The faults and folds verge mainly to the E with mean NE to SW non-linear trend, and seem to curve around the basin to the south. Preliminary exhumation ages are Eocene in the Macon Range and young eastward with some late stage contractional structures forming in the upper part of the stratigraphic section post mid-late Miocene. Future fieldwork will further test whether or not the basin conforms to the small-scale drip model predictions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T43B2081B
- Keywords:
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- 8102 TECTONOPHYSICS / Continental contractional orogenic belts and inversion tectonics