Andean surface uplift constrained by radiogenic isotopes of arc lavas

Climate and tectonics have complex feedback systems which are difficult to resolve and remain controversial. Current paleoelevation proxies are contentious because of difficulties in correcting for past climate conditions. We propose a new climate-independent approach to constrain Andean Plateau surface uplift. 87Sr/86Sr and 143Nd/144Nd ratios of Quaternary frontal arc lavas from within the Andean Plateau have a distinct isotopic signature (>0.705 and <0.5125, respectively) which we identify as a plateau discriminant. Strong linear correlations exist between volcano base elevation and 87Sr/86Sr (R2=0.803, n=18) and 143Nd/144Nd (R2=0.754, n=17) of non-plateau arc lavas. With these relationships, we constrain 200 Myr of surface uplift history for the Western Cordillera and Andean arc using new geochemical data for Paleogene lavas and a compilation of age corrected isotope compositions. By 23 Ma the central Andean arc was in a tectonic plateau setting with elevations comparable to present day (3500-5100 m) between at least 16 and 28oS. From 23 to 10 Ma, surface uplift propagated southward by approximately 400 km. We suggest that the presence of hot, weak lower crust in orogenic plateaux is key to enhancing crustal contributions to arc magmatism in such settings. There is potential for this approach to be applied to constrain surface uplift of other active and ancient arcs.