The composition and weathering of the continents over geologic time

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Authors

Alex Lipp , Oliver Shorttle , Erik Sperling, Jochen J Brocks, Devon Cole, Peter Crockford , Lucas Del Mouro, Keith Dewing, Stephen Q Dornbos, Joseph F. Emmings

Abstract

The composition of continental crust records a history of construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how both igneous addition and chemical weathering have modified the continents bulk composition are essential for understanding the evolution of geodynamics and climate. We have extracted temporal trends in sediments protolith composition and weathering intensity from the largest available compilation of sedimentary major-element compositions, of ~ 15,000 samples from 4.0 Ga to the present. To do this we used a new analytical method which inverts whole sedimentary compositions for protolith composition and weathering intensity simultaneously. We find that the average Archean upper continental crust was silica rich and had a similar compositional diversity to modern continents. This is consistent with an early-Archean, or earlier, onset of plate tectonics. In the Archean, chemical weathering was ~ 25 % more efficient at sequestering CO2 than in subsequent time periods. Since 2.0 Ga, over long (> 0.5 Ga) timescales, the crustal weathering intensity has remained largely constant. On shorter timescales over the Phanerozoic, the intensity of weathering is correlated to global climate state, consistent with silicate weathering feedback acting in response to changes in CO2 outgassing.

DOI

https://doi.org/10.31223/osf.io/qhtb6

Subjects

Earth Sciences, Geochemistry, Physical Sciences and Mathematics

Keywords

archean continents, crustal evolution, phanerozoic climate, plate tectonics, provenance, sedimentary geochemistry, weathering

Dates

Published: 2020-08-21 16:35

Last Updated: 2020-08-21 18:25

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License

GNU Lesser General Public License (LGPL) 2.1

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