Paleozoic to early Cenozoic cooling and exhumation of the basement underlying the eastern Puna plateau margin prior to plateau growth

Abstract

Constraining the pre-Neogene history of the Puna plateau is crucial for establishing the initial conditions that attended the early stage evolution of the southern extent of the Andean plateau. We apply high-to low-temperature thermochronology data from plutonic rocks in northwestern Argentina to quantify the Paleozoic, Mesozoic and early Tertiary cooling history of the Andean crust. U-Pb crystallization ages of zircons indicate that pluton intrusion occurred during the early mid-Ordovician (490-470Ma) and the late Jurassic (160-150Ma). Lower-temperature cooling histories from 40 Ar/ 39 Ar analyses of K-feldspar vary substantially. Basement rocks underlying the western Puna resided at temperatures below 200C (<6km depth) since the Devonian (∼400Ma). In contrast, basement rocks underlying the southeastern Puna were hotter (∼200-300C) throughout the Paleozoic and Jurassic and cooled to temperatures of <200C by ∼120Ma. The southeastern Puna basement records a rapid cooling phase coeval with active extension of the Cretaceous Salta rift at ∼160-100Ma that we associate with tectonic faulting and lithospheric thinning. The northeastern Puna experienced protracted cooling until the late Cretaceous with temperatures <200C during the Paleocene. Higher cooling rates between 78 and 55Ma are associated with thermal subsidence during the postrift stage of the Salta rift and/or shortening-related flexural subsidence. Accelerated cooling and deformation during the Eocene was focused within a narrow zone along the eastern Puna/Eastern Cordillera transition that coincides with Paleozoic/Mesozoic structural and thermal boundaries. Our results constrain regional erosion-induced cooling throughout the Cenozoic to have been less than ∼150C, which implies total Cenozoic denudation of <6-4km. © 2012. American Geophysical Union. All Rights Reserved.