Joint 118th Annual Cordilleran/72nd Annual Rocky Mountain Section Meeting - 2022

Paper No. 12-5
Presentation Time: 3:25 PM


EDEN, Ryan, Department of Earth Science, University of California, Santa Barbara, 1006 Webb Hall, University of California, Santa Barbara, CA 93106, SUNDELL, Kurt E., Department of Geosciences, Idaho State University, 921 S. 8th Ave. Stop 8072, Pocatello, ID 83209, GEHRELS, George E., Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721 and SAYLOR, Joel E., Department of Earth, Ocean and Atmospheric Sciences, University of British Colombia, Vancouver, BC V6T 1Z4, Canada

The relationship between surface uplift and crustal thickening in the building of extreme (>3 km) elevation in the central Andes is debated. End member hypotheses include (1) coupled pure shear crustal thickening and concomitant slow (i.e., km/10’s Myr) surface uplift; and (2) decoupled crustal thickening and rapid (i.e., km/Myr) surface uplift driven by foundering of mantle lithosphere. We tested these with new laser ablation ICP-MS Lu-Hf isotopic analysis of zircons sampled from ignimbrite deposits in Oligocene – Miocene hinterland basins in the Western Cordillera of southern Peru, interpreted in the context of igneous whole rock geochemical data. Pulsed juvenile magmatism is roughly coeval with a transition in hinterland basin deposition, from fluvial to evaporitic-lacustrine, and with recently reported rapid surface uplift between 22 and 10 Ma. Results support a decoupling between crustal thickening and surface uplift in the northern CAP during the late Cenozoic due to the formation and subsequent foundering of dense lower lithosphere via Rayleigh-Taylor instability, after protracted crustal thickening and shortening.