Low-temperature thermochronology in the Peruvian Central Andes: implications for long-term continental denudation, timing of plateau uplift, canyon incision and lithosphere dynamics

Abstract

Abstract: In Peru, the western edge of the 4.5 km high Western Cordillera is cut by a >3 km deep canyon. To understand incision by the Cotahuasi–Ocoña River and the regional uplift history of this orogenic plateau capped by volcanic rocks, 26 crystalline rock samples were collected for low-temperature thermochronology from vertical profiles parallel and perpendicular to the canyon. Rock cooling histories confirm that most plateau denudation had occurred prior to 24 Ma but plateau incision peaked after c . 14–9 Ma in response to rapid surface uplift. The abrupt occurrence of a rock heating event is also detected during middle Miocene time. This was either a response to the emplacement of low-conductivity, regionally extensive ignimbritic caprock or a response to crustal-scale fluid circulation caused by wet melting of the overriding plate when magmatism resumed c . 24 Ma. The potential for thermochronology to provide information on past geothermal gradients is discussed, showing how it can be used as a proxy for understanding change in subducting slab dynamics, with oscillations in subduction angle having perhaps been the main on–off switch for magmatism in this Cordilleran setting. Supplementary material: Fission-track and apatite (U–Th)/He results and apatite chemistry indicators are available at http://www/geolsoc.org.uk/SUP18405 .