Geochemical fingerprints and tectonic setting of the Late Palaeozoic marginal basin of the Bariloche Complex (SW Gondwana), North Patagonian Andes of Argentina

Abstract

The understanding of the Late Palaeozoic evolution of the south-western Gondwana margin is limited due to a lack of outcrops and data. New insights were achieved by fieldwork, petrographic characterization and geochemical fingerprinting on metasedimentary and interlayered metabasic rocks of the Bariloche Complex exposed in the North Patagonian Andes (~41°S). The surveyed areas were the Jakob-Témpanos lakes (JKB), Cerro Catedral (CAT), and the western foothills of the Ventana Range (VR). The basin was primarily supplied with immature detritus, which formed lithic sandstones, greywackes, pelites and, to a lesser extent, quartzose arenites. The metabasites in the JKB area derived from N-MORB tholeiites produced by low-pressure melting of a depleted mantle with a subduction component. In contrast, metabasites in the VR and CAT area can be traced back to OIB alkaline and E-MORB alkaline/tholeiitic transitional deeper magma sources. A micaschist of the VR yielded a U-Pb detrital zircon maximum depositional age of 358 ± 4 Ma (2σ). Moreover, a 206Pb/238U preferred age of 330 ± 6 Ma is likely explained by a mixed isotopic signal resulting from a late metamorphic/thermal overprint, or Pb loss in the metasediment zircons. These results, compared with neighbouring Late Palaeozoic regions, constrain the lifetime of a back-arc basin until its closure at the beginning of the Gondwanide orogeny.