Apatite triple dating and white mica ⁴⁰Ar/³⁹Ar thermochronology of syntectonic detritus in the Central Andes: A multiphase tectonothermal history

Abstract

We applied apatite U-Pb, fission track, and (U-Th)/He triple dating and white mica ⁴⁰Ar/³⁹Ar thermochronology to syntectonic sedimentary rocks from the central Andean Puna plateau in order to determine the source-area geochronology and source sedimentary basin thermal histories, and ultimately the timing of multiple tectonothermal events in the Central Andes. Apatite triple dating of samples from the Eocene Geste Formation in the Salar de Pastos Grandes basin shows late Precambrian–Devonian apatite U-Pb crystallization ages, Eocene apatite fission track (AFT), and Eocene–Miocene (U-Th)/He (ca. 8–47 Ma) cooling ages. Double dating of cobbles from equivalent strata in the Arizaro basin documents early Eocene (46.2 ± 3.9 Ma) and Cretaceous (107.6 ± 7.6, 109.5 ± 7.7 Ma) AFT and Eocene–Oligocene (ca. 55–30 Ma) (U-Th)/He ages. Thermal modeling suggests relatively rapid cooling between ca. 80 and 50 Ma and reheating and subsequent diachronous basin exhumation between ca. 30 Ma and 5 Ma. The ⁴⁰Ar/³⁹Ar white mica ages from the same samples in the Salar de Pastos Grandes area are mainly 400–350 Ma, younger than apatite U-Pb ages, suggesting source-terrane cooling and exhumation during the Devonian–early Carboniferous. Together these data reveal multiple phases of mountain building in the Paleozoic and Cenozoic. Basin burial temperatures within the plateau were limited to <80 °C and incision occurred diachronously during the Cenozoic.