Tracking Basin Inversion in the RetroArc Foreland Basin: Integrated Provenance Studies in the Cachueta Basin, South-Central Andes
Mahoney, J. Brian
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The Cachueta basin, east of Mendoza, Argentina, records a detailed history of rapid exhumation of the Andean orogenic system at 33°S. The integration of sedimentologic, stratigraphic, geochronologic, and thermochronologic studies constrains the pattern of orogenic exhumation. The Cacheuta basin can be subdivided into five distinct lithofacies [Mariño, La Pilona, Tobas Angostura, Río de los Pozos, and Magotes] that reflect episodic sediment flux produced during orogenic exhumation. Provenance analysis identifies clastic detritus derived from the Cordillera Costal (Jura-Cretaceous zircon), Cordillera Principal (distinctive Jurassic conglomerate, Cretaceous fossiliferous limestone, and Tertiary hornblende andesite clasts), Cordillera Frontal (PermoTriassic clasts and detrital zircon) and the Precordillera (Devonian to late Paleozoic meta-sedimentary detritus). The dramatic influx of coarse clastic debris at the Mariño/Pilona contact reflect major changes in provenance related to eastward propagation of the fold and thrust belt beginning at ~16 Ma. Detrital U/Pb and (U-Th)/He analyses constrains the pattern of basin subsidence and exhumation. Initial basin subsidence is constrained by a ca. 19.2 Ma U/Pb age from a volcanic tuff near the base of the succession. Coeval U/Pb zircon and (U-Th)/He apatite ages in strata younger than 9.9 Ma constrain the timing of basal sedimentation and associated volcanism. Conversely, strata older 9.9 Ma contain maximum depositional U/Pb zircon ages of 19.2 to 9.9 Ma, and (U-Th)/He apatite ages of 5-8 Ma, which are interpreted to reflect basin inversion.
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