Peruvian Altiplano Stratigraphy Highlights Along-Strike Variability in Foreland Basin Evolution of the Cenozoic Central Andes

Retroarc foreland basins in the Andean plateau contain critical information on geodynamic processes driving plateau development by providing a record of exhumation and sediment sourcing, as well as the timing, location, and magnitude of basin subsidence. However, this record is incomplete along orogenic strike and particularly limited in southern Peru. We measured similar to 6,200m of nonmarine clastic strata in the northern Peruvian Altiplano, documented through lithofacies characterization and paleocurrent analysis, conglomerate clast counts, sandstone petrography, and detrital zircon U-Pb geochronology; for the latter we employ quantitative detrital zircon interpretation methods including multidimensional scaling, mixture modeling, and quantification of zircon roundness. Results show dominant sediment sourcing from the Western Cordillera and/or western Altiplano. Sediment accumulation rates define an upward-convex Paleogene subsidence profile consistent with deposition in a northeastward-migrating flexural foreland basin system, with lithospheric loading from an increasingly proximal Western Cordilleran hinterland. Basin deposition following a 23-9Ma angular unconformity shows a marked increase in sediment accumulation rates >800m/Myr, interpreted as a departure from flexural subsidence. Results highlight along-strike variability in Andean foreland basin evolution, as foredeep deposits are thicker, and the onset of rapid sediment accumulation occurs earlier in southern Peru compared to Bolivia and Argentina. Results tentatively support models of orogenic cyclicity and reveal that episodes of high-flux magmatism in southern Peru are slightly out of phase with those documented in northwest Argentina, which may be controlled by preexisting Paleozoic-Mesozoic structural and stratigraphic fabrics and the rate of underthrusting of melt-fertile continental lower crust and mantle lithosphere.