Fig. 4

Baseline Sr and Nd isotopes as a plateau discriminant and palaeoelevation proxy. a, b Baseline isotopic compositions within each volcanic zone vary little with differentiation from basaltic andesite to rhyolite⁴⁶; even the least silicic CVZ rocks are enriched in ⁸⁷Sr/⁸⁶Sr (>0.7050) and depleted in ¹⁴³Nd/¹⁴⁴Nd (<0.5125). c, d Baseline isotope compositions compared to smoothed elevation. Elevation smoothed to a radius of 37.5 km was calculated from the Shuttle Radar Topography Mission DEM (SRTM1, pixel resolution 90 m⁷¹). A radius of 37.5 km is selected as this is half of the maximum crustal thickness in the Andes. Smoothing to this degree filters out non-isostatic, short wave-length topography. 95% confidence intervals are represented as dashed lines (excluding samples south of 38.5°S, see text). Volcano locations are shown on Fig. 1a. Symbols are bigger than the maximum analytical error isotope on isotope data, except where shown. Typical quoted analytical precision on SiO₂ compositions are ~3% RSD. All data shown here are presented in Supplementary Data 2