PRECIPITATION HYDROGEN ISOTOPE RECORDS TRACK TOPOGRAPHY OF THE EVOLVING ANDEAN PLATEAU MARGIN

The long-term surface elevation of orogens affects local (e.g. distribution of rainfall, biodiversity and climate) but also global environmental conditions e.g. through atmospheric teleconnections. Similarly important, the surface elevation history of a region reflects the competing roles of geodynamic processes in crust and mantle and erosion at the Earth’s surface and, therefore, links interactions between lithospheric and climatic processes. Stable isotope paleoaltimetry relies on the systematic decrease in the heavy isotope (¹⁸O or D) of precipitation due to cooling of air parcels and associated condensation of water vapor during uplift. Given the right boundary conditions, the resulting oxygen (δ¹⁸O) or hydrogen (δD) isotope-elevation relationships are robust and permit to relate δ¹⁸O or δD of past rainfall to changes in surface elevation. Single-site records of δ¹⁸O or δD in precipitation, however, can be affected by climatic and topographic parameters some of which may have magnitudes much larger than can be accounted for by changes in regional surface uplift alone and isotope-elevation relationships may change over geologic time. Here we present δD (soil-derived n-alkanes, hydrated volcanic glass), δ¹⁸O (soil carbonates) and mean annual air temperature (branched GDGT) data that collectively permit paleoelevation reconstructions in the central Andes. In particular we track present-day isotope-elevation relationships along the windward side of the Eastern Cordillera from rainfall to soil proxies and evaluate past patterns of δD and δ¹⁸O in the geologic record of high-elevation basins along the Eastern Puna-Altiplano margin. Comparison of present-day rainfall and soil-derived n-alkane δD data documents the robustness of proxy data that average over extended time. Our data also document the impact of late Miocene surface uplift and changing paleoenvironmental parameters on δD values in precipitation. They also highlight the need for robust low-elevation δD and δ¹⁸O reference data that permit to evaluate differences in δD and δ¹⁸O between low and high elevation sites, in particular for settings where changes in topography are associated with changes in regional rainfall and atmospheric circulation patterns: a phenomenon common for most continental plateau margins.