Provenance of the Miocene Alto Tunuyan Basin (33 degrees 40 ' S, Argentina) and its implications for the evolution of the Andean Range: Insights from petrography and U-Pb LA-ICPMS zircon ages

Abstract

The Alto Tunuyan Foreland Basin in western Argentina is located immediately south of the flat-slab segment of the Central Andes and its evolution is directly related to the propagation of structures to the east. Petrographic and geochronologic studies have been performed to determine the provenance of syntectonic sediments in the basin in order to establish their relationship to the Andean orogenic activity. The analysed detrital and igneous zircons in contrast with previous data, allow us to restrict the basin age between ca. 15 and 6 Ma. Sandstones record two main contributions, one from andesitic volcanic rocks and the other from an acidic igneous source, the first probably corresponding to Miocene volcanic rocks from the Principal Cordillera (Farellones Formation) and the second to Permo-Triassic, acidic, igneous rocks from the Frontal Cordillera (Choiyoi Magmatic Province, CMP). Two secondary sources have been recorded, sedimentary and metamorphic; the first one is represented by Mesozoic rocks in the Principal Cordillera and the second by the Proterozoic/early Carboniferous Guarguaraz Complex (GC) in the Frontal Cordillera, respectively. Sandstones from the lower basin deposits (15-11 Ma) register supply pulses from the Farellones Formation reflecting the unroofing of the Principal Cordillera by uplift pulses during the middle Miocene. Sandstones from the upper basin deposits (ca. 11-9 Ma) record an increase in material derived from the CMP, reflecting important uplift of the Frontal Cordillera. A thick, ca. 9 Ma old ignimbrite within the basin indicates an eruption in the Frontal Cordillera. Detrital zircons from the CMP have been detected also in the lower basin deposits, suggesting either recycling of Mesozoic deposits containing CMP zircons or an early paleorelief of the Frontal Cordillera. The good correlation between the age of the detrital zircons of the CMP and the GC in the lower basin deposits supports recycling of Mesozoic sedimentary deposits.