Central Andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude (>2 km) Miocene-to-modern surface uplift. However, the isotopic relationships between precipitation, surface waters, and soil waters upon which these reconstructions are based remain poorly constrained for both past, and in many cases, modern conditions. We quantify the relationships between central Andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples (δ18O and δD) collected between April 2009 and October 2012. The isotopic compositions of stream waters match precipitation along the eastern flank. In contrast, Altiplano surface waters possess a lower δD-δ18O slope (4.59 vs ~8 for meteoric waters) not observed in precipitation, which signals heavy isotope evaporative enrichment in surface waters. Paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout Andean uplift, and that conditions may have been more evaporative when the Andes were lower. Thus, more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central Andean plateau proxy materials likely overstate Miocene-to-present surface uplift. We propose Altiplano paleoelevations of 1-2 km at 24.5 Ma, 1.5-2.9 km by 11.45 Ma, and modern elevations by ~6 Ma based on the lightest isotopic compositions observed in Altiplano proxy materials, which are least likely to be influenced by evaporation. These constraints limit total late-Miocene-to-modern uplift to <2.2 km, are more consistent with crustal shortening records, and suggest that plateau uplift may have been more spatially uniform than suggested by previous interpretations of stable isotope proxies.
Bibliographical noteFunding Information:
RPF received an NSF Graduate Research Fellowship Grant 2011094378 , and a Rackham International Research Grant from the Rackham Graduate School at the University of Michigan (UM). RPF and MLJ received support from Turner Graduate Student Research Grants from the UM Department of Earth and Environmental Sciences . CJP and TAE received support from NSF EAR Grants 0738822 and 0907818 ; CJP also received support through the UM Associate Professor Fund . We thank J. Tito, G. Gonzalez, S. Tawackoli, C.R. Tabor, J.B. Barnes, N. Insel, and M. Tracy for assistance in the field. The authors thank J.E. Saylor, an anonymous reviewer, and editor A. Yin for comments that improved this manuscript.
© 2015 Elsevier B.V..
- Central andes
- Pedogenic carbonate
- Stable isotope geochemistry
- Water isotopes