Chemical weathering response to tectonic forcing: A soils perspective from the San

abstract Article history:Received 30 July 2011Received in revised form 3 January 2012Accepted 9 January 2012Available online xxxxEditor: R.W. CarlsonKeywords:erosionchemical weatheringsoil productionkinetic limitationtectonics What controls the chemical weathering of soils in tectonically active landscapes? Recent field and modelingstudies suggest that tectonic forcing and associated increases in erosion rates may either promote or hindersoil chemical weathering. These competing trajectories are dependent on two primary controls: the availabilityoffreshmineralsandtheirresidencetimeonthelandsurface.Here,weexploreratesandextentsofsoilweatheringintheSanGabrielMountainsofCalifornia,wherepreviousworkhasmeasuredcleartectonicfingerprintsonratesof long term exhumation, hillslope erosion and landscape morphology. We quantify chemical weathering acrossthis landscape by elemental analysis of soils, saprolites and bedrock on six sites that bracket the low-gradienthillslopes of the relict upland plateau and the high-gradient hillslopes at the margins of the tectonically-drivenincising landscape. Average chemical depletion fractions, which measure weathering losses from soil relativeto unweathered parent material, decrease with increasing elevation and decreasing temperature, reflecting acombination of climate in fluence and potential dust inputs from the Mojave Desert. Weathering uxes fromnon-dust-affectedsiteswith similarelevations,climatesandlithologycorrelatewith botherosionratesandhill-slope gradient. On low-gradient hillslopes (b25°), weathering rates increase with increasing erosion rates,reflecting the influence of mineral supply. However, on high-gradient hillslopes (>25°), weathering intensitiesand rates both decrease as erosion rates increase and soils thin. At the highest denudation rates(>300 t km