Deep weathering in the semi-arid Coastal Cordillera, Chile

authored by

L. V. Krone, F. J. Hampl, C. Schwerdhelm, C. Bryce, L. Ganzert, A. Kitte, K. Übernickel, A. Dielforder, S. Aldaz, R. Oses-Pedraza, J. P. H. Perez, P. Sanchez-Alfaro, D. Wagner, U. Weckmann, F. von Blanckenburg

Abstract

The weathering front is the boundary beneath Earth’s surface where pristine rock is converted into weathered rock. It is the base of the “critical zone”, in which the lithosphere, biosphere, and atmosphere interact. Typically, this front is located no more than 20 m deep in granitoid rock in humid climate zones. Its depth and the degree of rock weathering are commonly linked to oxygen transport and fluid flow. By drilling into fractured igneous rock in the semi-arid climate zone of the Coastal Cordillera in Chile we found multiple weathering fronts of which the deepest is 76 m beneath the surface. Rock is weathered to varying degrees, contains core stones, and strongly altered zones featuring intensive iron oxidation and high porosity. Geophysical borehole measurements and chemical weathering indicators reveal more intense weathering where fracturing is extensive, and porosity is higher than in bedrock. Only the top 10 m feature a continuous weathering gradient towards the surface. We suggest that tectonic preconditioning by fracturing provided transport pathways for oxygen to greater depths, inducing porosity by oxidation. Porosity was preserved throughout the weathering process, as secondary minerals were barely formed due to the low fluid flow.

Organisation(s)

Institute of Geology

External Organisation(s)

Helmholtz Centre Potsdam - German Research Centre for Geosciences (GFZ)
Technische Universität Berlin
University of Tübingen
University of Atacama (UAD)
Universidad Austral de Chile
University of Potsdam
Freie Universität Berlin (FU Berlin)

Type

Article

Journal

Scientific Reports

Volume

11

ISSN

2045-2322

Publication date

22.06.2021

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

General

Sustainable Development Goals

SDG 13 - Climate Action

Electronic version(s)

https://doi.org/10.1038/s41598-021-90267-7 (Access: Open)