CENOZOIC EVOLUTION OF THE NORTHERN CENTRAL ANDEAN PLATEAU OF PERU (Invited Presentation)

We reconstruct the Cenozoic paleoelevation history of the northern central Andean plateau to decipher the tectonic mechanisms of plateau growth. Paleocene to Miocene records come from early foreland basin deposits to intermontane deposits as this region was incorporated into the Andean fold-thrust belt at ~36.5 Ma. We analyzed the δ¹⁸O values of authigenic carbonates from six formations deposited in the evolving foreland basin. A multiproxy analysis consisting of δ¹⁸O and Δ₄₇ values from authigenic carbonates, δ²H values from leaf wax n-alkanes, and pollen distribution from the intermontane Descanso-Yauri basin provides the Miocene-Pliocene record. The stable isotopic composition of meteoric water was reconstructed from the δ¹⁸O values of carbonate and leaf wax using paleotemperature from Δ₄₇ values. We used a range of meteoric water and temperature lapse rates to identify how elevation changed throughout the Cenozoic. The pollen assemblage provided an independent proxy for the elevation change during the Neogene. The reconstructed meteoric water δ¹⁸O from the foreland basin shows that surface elevation increased from sea level in the Paleocene to ~1.8–2.4 km in the late Miocene. The recorded paleoclimate changes from the hinterland basin point to a surface uplift of ∼2.5 ±1 km between ~10 and 6 Ma. Both of these records suggest that the northern central Andean plateau did not reach its modern elevation of ~4km until after contractional deformation had ceased in this region by ~9Ma. We postulate that upper crustal shortening was responsible for building the initial ~1.8–2.4 km elevation. Following that, piecemeal removal of the lower lithosphere, possibly in conjunction with lower/middle crustal flow from south to north in the central Andean plateau, raised this region to its modern elevation.