TY - JOUR

T1 - Deep weathering in the semi-arid Coastal Cordillera, Chile

AU - Krone, L. V.

AU - Hampl, F. J.

AU - Schwerdhelm, C.

AU - Bryce, C.

AU - Ganzert, L.

AU - Kitte, A.

AU - Übernickel, K.

AU - Dielforder, A.

AU - Aldaz, S.

AU - Oses-Pedraza, R.

AU - Perez, J. P. H.

AU - Sanchez-Alfaro, P.

AU - Wagner, D.

AU - Weckmann, U.

AU - von Blanckenburg, F.

N1 - Funding Information: This project is funded by German Science Foundation (DFG) grants within the priority program 1803 “Earth-Shape—Earth surface shaping by biota”. The authors would like to thank L. Paulino and T. Ehlers for their support in planning and performing the drilling campaign. Further, the authors are grateful to J. Kück for advice and assistance on the televiewer data, to K. Bauer for implementing the density calculation from logging data, and to J. Kallmeyer for assisting with the contamination control. The authors also thank the section Geomechanics and Scientific Drilling at the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences for using their facilities.

PY - 2021/6/22

Y1 - 2021/6/22

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85108778091&partnerID=8YFLogxK

U2 - 10.1038/s41598-021-90267-7

DO - 10.1038/s41598-021-90267-7

M3 - Article

VL - 11

JO - Scientific Reports

JF - Scientific Reports

SN - 2045-2322

IS - 1

M1 - 13057

ER -