Cenozoic Exhumation and Deformation of the Intermontane Pastos Chicos Basin in the Southern Central Andes: Implications for the Tectonic Evolution of the Andean Plateau (Puna) and the Eastern Cordillera Between 23° and 24°S, NW Argentina

The Andean Plateau of north-western Argentina (Puna) at a mean elevation of ca. 4.2 km constitutes the southern continuation of the Altiplano; it is a compressional basin-and-range province comprising fault-bounded, high-elevation mountain ranges and largely internally drained basins with often thick sedimentary and volcaniclastic fill. Growing sedimentological and structural evidence supports the notion that the north-western Argentine Andes between 22 degrees and 26 degrees S developed from an initial extensive broken-foreland system that extended across the present-day eastern Andean flank during the early to middle Eocene. However, compelling evidence of the tectonic history of this region is still missing. Here, we present new apatite fission track and zircon (U-Th)/He thermochronological data and U-Pb zircon ages from intercalated volcanic ash deposits from the Pastos Chicos Basin (23.5 degrees S, 66.5 degrees W) to constrain basin formation and the timing of major crustal deformation in the northern Puna. Inverse thermal modeling of the thermochronological data provides further temporal constraints on the late Cenozoic cooling history of the crust in this region and, by inference, on the timing of upper-crustal shortening, range uplift, and basin formation in the northern sector of the present-day Puna Plateau. Specifically, we argue for plateau-wide distributed deformation in the Eocene between 23 degrees and 24 degrees S, followed by spatially disparate and diachronous deformation (Oligocene to Pliocene).