T044-08
Cenozoic Tectonic Evolution of the Antofalla Basin in the Puna Plateau, NW Argentina

Monday, 14 December 2020: 16:53
Virtual
Mitchell McMillan, University of Toronto, Earth Sciences, Toronto, ON, Canada, Alexander Robert Robert Tye, University of Toronto at Mississauga, Chemical and Physical Sciences, Mississauga, ON, Canada, Lindsay M Schoenbohm, Univ. of Toronto Mississauga, Toronto, ON, Canada; University of Toronto, Department of Earth Sciences, Toronto, ON, Canada, Renjie Zhou, The University of Queensland, School of Earth and Environmental Sciences, St. Lucia, Australia and Malcolm F McMillan, University of Melbourne, School of Earth Sciences, Parkville, VIC, Australia
Recorded Presentation
Abstract:
The Altiplano-Puna Plateau in the Central Andes is the type-example of a hinterland plateau in a Cordilleran orogen. The spatial and temporal history of Cenozoic uplift in the southern Puna, however, is controversial, and the geodynamic drivers of plateau uplift remain elusive. Upper crustal shortening and syn-tectonic sedimentation provide constraints on the uplift of major ranges on the plateau. Here we present detailed geologic mapping and structural cross-sections of the Antofalla basin, a Paleogene to Quaternary basin in the core of the southern Puna orogenic hinterland, to refine the history of Cenozoic uplift.

The Antofalla basin is situated west of the Sierra de Calalaste, a major contractional range with dominantly east-dipping reverse faults. New detrital zircon U/Pb ages and mapping of syn-tectonic strata reveal a phase of E-W shortening on a major fault system west of the modern Sierra de Calalaste during the Late Oligocene to Early Miocene. Contractional deformation propagated ~30 km westward from the Sierra de Calalaste to the Salina del Fraile between ca. 24 and 17 Ma, likely utilizing pre-existing, east-dipping planes of weakness in the basement. After a Middle Miocene tectonic and depositional hiatus, deformation stepped back eastward to the Calalaste, where Late Miocene–Pliocene alluvial to lacustrine strata were deposited in a narrow, restricted basin on the western flank of the range. In a separate presentation [1] we argue that sedimentation was triggered by an episode of extension, also reflected by the development of a set of normal faults accommodating ~10% E-W extension. Folding and of Late Miocene strata indicates a return to a compressional regime by the Quaternary or earlier.

We suggest that the region was deformed during the Oligocene to Miocene as a west-vergent, westward-propagating wedge, and was topographically high during the Middle to Late Miocene. This topographic welt was interrupted by transient E-W extension beginning in the Late Miocene, and E-W shortening was renewed by the Quaternary. We consider the tectonic and geodynamic implications of this sequence of deformation within a region of extensive back-arc volcanism in the Andean hinterland.

[1] Tye, A., McMillan, M., & Schoenbohm, L. M., “Salar de Antofalla depression, Puna Plateau, Argentina...”.

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