INTEGRATED PROVENANCE ANALYSIS OF THE LATE PALEOZOIC PAGANZO BASIN, SIERRAS PAMPEANAS: IMPLICATIONS FOR PALEOGEOGRAPHIC RECONSTRUCTION OF THE WESTERN GONDWANAN MARGIN

The Sierras Pampeanas province (Argentina; 26°–33°S) is a modern (Miocene-recent) archetype for lithospheric response to flat-slab subduction, yet studies of fault reactivation and basin inversion have been hindered by sediment recycling driven by Paleozoic-Mesozoic continental growth and rifting. A near-continuous Lower Carboniferous – Upper Permian sedimentary record of the Paganzo Basin gives insight into earliest tectonism and paleogeography of western Gondwana ~300 Ma. Debate surrounds the Paganzo Basin’s tectonic origin having been interpreted as a retroarc foreland basin resulting from western-flanking volcanism, or a rapidly subsidizing pull-apart rift basin system. We present preliminary results of an integrated provenance study from four localities across the Paganzo Basin. Newly measured and correlated stratigraphic sections characterize a transition from diamictites, shales, and fine-grained sandstones of the Upper Mississippian (Lower Guandacol and Agua Colorada Formations) to Lower Pennsylvanian wavy-bedded sandstones and conglomerates (Upper Guandacol, Volcán, Panacán, and Tupe Formations). These observations support the interpretation of a transgression from glaciomarine to terrestrial environments. Detrital zircon U-Pb geochronology age spectra from these four basin localities will improve existing estimates of maximum depositional ages and capture upsection patterns in sediment source contributions during regional Early-Middle Pennsylvanian drainage integration. Three morphotectonic units comprise the Paganzo Basin’s primary sediment sources: the subduction-related Cambrian Pampean Orogen, Ordovician Famatinian magmatic belt, and Silurian-Devonian Proto-precordillera. Generally, sandstone compositions exhibit a transition from quartzolithic to quartzofeldspathic. Early basin infilling from the Proto-precordillera via glaciomarine processes resulted in recycled orogen input, followed by progressive input of Pampean-Famatinian arkosic sediment. An integrated, basin-scale provenance history is needed to provide a framework for the Paganzo Basin’s formation and evolution. This framework provides context for future work in differentiating multi- and first-cycle sediment histories via combined geo- and thermochronology techniques.