Climate and tectonic evolution of the Descanso-Yauri basin in the northernmost Altiplano: Archetype example of a ‘lithospheric drip’ basin

Abstract:

We present a new multiproxy Miocene–Pliocene paleoelevation record of the northernmost Altiplano plateau reconstructed from pollen, clumped isotope (TΔ₄₇) and δ¹⁸O_c of sedimentary carbonates and leaf wax n-alkane δD signatures. The ~18Ma to ~9Ma deposits of our study area, Descanso–Yauri basin in southern Peru show 11 to 16ºC warmer than modern mean annual air temperature, low elevation vegetation pollen assemblage (dominated by Podocarpus), and an average precipitation δ¹⁸O_mw (VSMOW) value of -8.3±2.0‰ (2σ). The ~5 to 4 Ma deposits in the Descanso-Yauri basin are characterized by herb and shrub vegetation and an average δ¹⁸O mw (VSMOW) value of -14.6±3.0‰ (2σ), indicative of an elevation and/or climate similar to modern conditions. Based on the multiproxy paleoclimate record, we interpret that there was a 2±1 km surface uplift between 9 and 5 Ma in the northernmost Altiplano plateau. Deformation history analysis through map scale structural investigation combined with provenance analysis from conglomerate clast composition and paleocurrents show that the thrusts bounding the NE side of the Descanso-Yauri basin were active until ∼9Ma. Deformation waned afterwards, and switched to an extensional deformation regime, coincident with decrease in subsidence rate from ∼0.2mm/year to ∼0.03mm/year. Depositional history reconstructed by facies analysis and stratigraphic correlation reveal that deposition in the basin began with transverse braided river systems that formed along the thrust front and gave way to a larger fluvial-lacustrine system until ∼4 Ma. The basin deposits show an overall fining upward trend from coarse clastic dominated, in the lower most parts of the basin fill to fluvial overbank and lacustrine mudstone and diatomite deposits in the middle-upper parts. The thickest deposits formed in the central part of the basin. Based on these depositional and deformational patterns, we infer that the Descanso-Yauri basin formed in response to a growing eclogite and mantle root in the lower lithosphere. Removal of this root, possibly combined with lower crustal flow, led to the rapid 9-5 Ma surface uplift of the northernmost part of the Central Andean Plateau.