Deciphering the Spatial and Temporal Nature of the Surface Uplift in the Altiplano Plateau

Abstract:

The surface uplift history of the Altiplano plateau is widely debated. Two end-member models favor: a slow and gradual surface uplift from ~45Ma by distributed shortening; and pulsed rapid surface uplift between 16–9 Ma and 10–6 Ma in the southern and central plateau respectively by lower lithospheric removal. To better elucidate the along strike nature of the surface uplift, we extended the elevation and deformation history to the early to late Cenozoic basins in the northernmost part of the Central Andean plateau, inferred to have formed in the foreland, wedgetop, and hinterland settings of the Andean fold-thrust belt in southern Peru.

Increasing deformation related to propagation of the foreland basin system is shown by early Paleocene backbulge Quilque to the late Eocene wedgetop Soncco formations. The lowest elevation (sea level) is recorded by marginal marine deposits of Quilque. The ð¹⁸O of meteoric water (ð¹⁸O_mw) reconstructed from sedimentary carbonates show similar average values with -6.7 ±1.9‰ in late Paleocene Chilca to -8.1 ±2.6‰ in middle Miocene Paruro formations, suggesting a middle Miocene paleoelevation of 1.1 ±1.0 km (2σ) in first order approximation.

In members A, B and C of Miocene–Pliocene Descanso Yauri basin, A and B are deformed and C is relatively undeformed and flat lying. A, B and the lower C deposits are fluvial and middle–upper C deposits are lacustrine. The ð¹⁸O_mw from B and C carbonates show averages of -8.4 ±1.1‰ and -9.7 ±3.1‰; the large range in C (-5.5‰ to -14.7‰) is tentatively interpreted as a result of high altitude precipitation, modified by evaporative enrichment within the lake system. Reconstructed MAAT from Δ₄₇ of carbonates and ðD of plant waxes show similar results in B (29.1±5.0°C, -146.6±10.9‰) and ~9Ma lower C (23.1 ±1.9°C, -149.6±9.7‰), and a large shift in ðD to -206.7±13.0‰ in upper diatomaceous non-calcareous C (minimum U-Pb zircon age constraint of 4.3 ±0.3 Ma, 2σ). Therefore, we infer that the northernmost part of the plateau experienced a pulse of rapid surface uplift between ~9–4 Ma, possibly as a result of the lower lithosphere removal and south to north lower crustal flow. The timing is consistent with the north-central Altiplano, although possibly slightly later, and suggests that a regional-scale phenomenon resulted in surface uplift.