Tectonic and climatic controls on late Cenozoic intra-arc basin development in the central Andes of southern Peru

Abstract

Intra-arc basin strata document the interplay between tectonics and climate in the central Andes. This is exemplified by a shift from fluvial to lacustrine-evaporitic depositional environments recorded in the 2.6 km-thick siliciclastic-carbonate basin fill of the Tincopalca Basin located in the Western Cordillera of southern Peru (∼16°S). Detrital zircon U-Pb geochronology yields age distributions dominated by syndepositional volcanism; maximum depositional ages bracket deposition between 28 and 21 Ma. A decrease in lacustrine carbonate δ¹⁸O values from ∼0 ‰ to -9 ‰ at 22–21 Ma, synchronous with lithologic evidence for basin closure can be explained by two nonunique interpretations: (1) prior attainment of high elevations in the Eastern Cordillera and attendant westward penetration of isotopically depleted eastern moisture, and/or (2) attainment of sufficient elevation in the Western Cordillera to exclude enriched western moisture. Results do not discriminate between rapid, large-magnitude surface uplift versus attainment of a threshold, moisture-blocking elevation in the Western Cordillera. Zircon εHf(t) in the Western Cordillera increases from -8 to 0 between 25 and 18 Ma, consistent with formation and subsequent removal of a lithospheric instability. Combining new and published data highlights the complex interactions between tectonics and climate in the following scenario. (1) Instability formation drove basin subsidence at 28–20 Ma. (2) Instability removal slowed subsidence during a transition to depleted eastern moisture, coeval with increasing zircon εHf(t) at 20–17 Ma and concomitant rapid surface uplift at 18–16 Ma. (3) Basin ponding and aridification occurred after 16 Ma in a deepening central Andean rain shadow.