T21B-2817
Regional Deformation of the Southern Puna Plateau, Central Andes, Recorded by Basin Evolution and Bedrock Exhumation History

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Renjie Zhou1, Lindsay M Schoenbohm1, Edward R Sobel2, Barbara Carrapa3, Donald W Davis1, Johannes Glodny4 and Daniel F Stockli5, (1)University of Toronto, Department of Earth Sciences, Toronto, ON, Canada, (2)University of Potsdam, Institute of Earth and Environmental Sciences, Potsdam, Germany, (3)University of Arizona, Geosciences, Tucson, AZ, United States, (4)Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Section 4.2, Potsdam, Germany, (5)Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States
Abstract:
The regional deformation history of the southern Puna Plateau remains poorly constrained but is key to understanding the growth and dynamics of the central Andes, an important example of orogeny along a non-collisional plate boundary.

Several lines of evidence lead us to propose that the southern Puna Plateau was occupied by an uninterrupted sedimentary basin during the late Eocene to early Oligocene (~38-28 Ma). First, oldest strata in the Antofagasta de la Sierra region (SW Puna) and the Pasto Ventura region (SE Puna) both contain little volcanic material, suggesting they predate the most recent arc activity at ~28 Ma. Second, detrital zircons from the Antofagasta de la Sierra region yield youngest U-Pb ages of ~39 Ma and detrital apatites from the Pasto Ventura region yield youngest fission-track ages of ~38 Ma, giving a maximum depositional age. Third, provenance analysis reveals a single, western source for the Antofagasta de la Sierra region (SW Puna) and dual, eastern and western sources for the Pasto Ventura region (SE Puna), supporting the presence of a regional basin.

This regional basin was disrupted and compartmentalized by uplift of ~N-S trending bedrock ranges starting as early as in late Oligocene time. Bedrock samples from the eastern foot of the Sierra de Calalaste (SW Puna) yield an apatite (U-Th-Sm)/He age of 19.9±2.0 Ma, consistent with modeled apatite fission-track data that show onset of exhumation at ~25-20 Ma. Modeling of apatite fission-track and (U-Th-Sm)/He data shows that the Sierra Laguna Blanca (SE Puna) experienced exhumation at ~15-10 Ma, the youngest bedrock exhumation documented in the plateau region, implying that deformation and erosion of basement-bounding structures continued into the middle Miocene.

We suggest that the post-late Eocene regional deformation history of the southern Puna Plateau documents an important dynamic shift from flexure-controlled foreland dynamics to flexure-limited broken foreland dynamics during the Oligocene.

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