Transient glacial incision in the Patagonian Andes from ~6 Ma to present

C D Willett; K F Ma; M T Brandon; J K Hourigan; E C Christeleit; D L Shuster

doi:10.1126/sciadv.aay1641

Transient glacial incision in the Patagonian Andes from ~6 Ma to present

Sci Adv. 2020 Feb 12;6(7):eaay1641. doi: 10.1126/sciadv.aay1641. eCollection 2020 Feb.

Authors

C D Willett^{1

2}, K F Ma³, M T Brandon³, J K Hourigan⁴, E C Christeleit³, D L Shuster^{1

2}

Affiliations

¹ Department of Earth and Planetary Science, 307 McCone Hall, UC Berkeley, Berkeley, CA 94720, USA.
² Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
³ Department of Geology and Geophysics, Yale University, 210 Whitney Ave., New Haven, CT 06511, USA.
⁴ Earth and Planetary Sciences Department, UC Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA.

Abstract

We report a mountain-scale record of erosion rates in the central Patagonian Andes from >10 million years (Ma) ago to present, which covers the transition from a fluvial to alpine glaciated landscape. Apatite (U-Th)/He ages of 72 granitic cobbles from alpine glacial deposits show slow erosion before ~6 Ma ago, followed by a two- to threefold increase in the spatially averaged erosion rate of the source region after the onset of alpine glaciations and a 15-fold increase in the top 25% of the distribution. This transition is followed by a pronounced decrease in erosion rates over the past ~3 Ma. We ascribe the pulse of fast erosion to local deepening and widening of valleys, which are characteristic features of alpine glaciated landscapes. The subsequent decline in local erosion rates may represent a return toward a balance between rock uplift and erosion.

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