EXHUMATION AND FOREARC DRAINAGE REORGANIZATION IN RESPONSE TO FLAT SLAB SUBDUCTION, PERUVIAN FLAT SLAB
Geochronologic results suggests that arc shutoff initiated at ~10 Ma in the north, and propagated southward through time. Thermochronometric results record cooling related to flat slab subduction, with Miocene and younger apatite (U-Th)/He cooling ages above the flat slab, and older ages to the south. The young cooling ages could be the product of increased exhumation and/or a lower geothermal gradient during flat slab subduction. However, geomorphic indices including hypsometric profiles and catchment-averaged channel steepness on forearc drainages suggest steeper, more youthful drainage networks above the flat slab, and generally higher erosion rates. The geomorphic indices are consistent with renewed exhumation and surface uplift driven by slab flattening. Moreover, many of the young cooling ages are in regions that lack recently active (Miocene and younger) upper crustal faults. We use these findings to evaluate potential processes that may enhance exhumation during flat slab subduction, including upper crustal shortening, dynamic topography, ridge buoyancy, and displacement of mid-to-lower crust via basal shear.