VARIABLE SURFACE UPLIFT ALONG AND ACROSS THE CENTRAL ANDES: A RE-EVALUATION OF EMPIRICALLY DERIVED ISOTOPIC LAPSE RATES APPLIED TO HYDRATED VOLCANIC GLASS

The Central Andes host Earth’s second largest orogenic plateau. Most believe the extreme elevation of the Central Andes was attained in the late Cenozoic; however, the timing and rate of surface uplift remains debated. Although a myriad of proxies has been used in attempt to reconstruct the surface uplift history of the Central Andes, a common challenge remains in estimating surface uplift patterns from reconstructed paleowater, which require the application of an isotopic lapse rate. We present results on modern water data from river and stream samples from the northern Central Andes and adjacent eastern lowlands, with several transects spanning ~4000 m in elevation, in attempt to quantify stable isotopic variations in δ¹⁸O and δD. We use these data to determine surface uplift patterns from paleowaters preserved in hydrated volcanic glass, with age control provided by zircon U-Pb geochronology. Watershed analysis provides critical insights into the highly variable elevations from which the water samples were sourced. Results show that empirically derived modern lapse rates are similar to lapse rates from thermodynamic and general circulation models. Volcanic rocks in the Andean plateau of Peru and Bolivia span ~25 Ma to near modern. Application of re-calibrated modern lapse rates highlights the along and across strike variability in the timing and rate of surface uplift. Spatially and temporally variable surface uplift of the Central Andes requires different geodynamic processes to explain patterns of surface uplift. The onset of hyper arid conditions along the Central Andean Pacific coast coincides with the attainment of moderate to high elevation.