GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 218-6
Presentation Time: 2:50 PM


SUNDELL, Kurt E.1, SAYLOR, Joel E.2, LAPEN, Thomas J.2 and HORTON, Brian K.3, (1)Department of Geosciences, University of Arizona, Tucson, AZ 85721, (2)Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, (3)Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712 – 1722

Estimates of temporal and spatial changes in Earth’s surface elevation are critical for understanding the lithospheric-scale geodynamic processes that drive surface uplift and in turn modulate regional climate patterns. We compare hydrogen isotopic compositions of hydrated volcanic glasses and modern stream waters to document late Cenozoic surface uplift across the central Andes of southern Peru. Elevations calculated from modern stream water isotopic compositions reproduce mean catchment elevations to a precision better than ± 500 m at 1σ. Glass isotope data show a spatiotemporally variable transition from isotopically heavy to isotopically light compositions that are consistent with modern water at high elevations. Volcanic glass stable isotopic compositions, interpreted in the context of published paleoelevation estimates and ancillary geological information, indicate that elevation rapidly increased by 2–2.5 km from 22–17 Ma in the central Western Cordillera (15–15.5°S), and from 15–10 Ma in the southern Western Cordillera (15.5–17°S) and Altiplano. Early Miocene Western Cordilleran uplift patterns are consistent with foundering of mantle lithosphere via Rayleigh-Taylor instability, whereas middle–late Miocene Altiplano and Western Cordillera uplift may be attributable to either lithospheric foundering or northward lower crustal flow from the overthickened Bolivian orocline. The Eastern Cordillera was slowly elevated by 1.5–2 km between 25 and 10 Ma, a rate consistent with crustal shortening as the dominant driver of surface uplift. West of the Abancay deflection, the Ayacucho region attained modern elevation by at least 22 Ma. The timing of orographic development across southern Peru is consistent with the early Miocene onset and middle Miocene intensification of hyperarid conditions along the central Andean Pacific coast.