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TitleThe composition and weathering of the continents over geologic time
 
AuthorLipp, A G; Shorttle, O; Sperling, E A; Brocks, J J; Cole, D B; Crockford, P W; Del Mouro, L; Dewing, KORCID logo; Dornbos, S Q; Emmings, J F; Farrell, U C; Jarrett, A; Johnson, B W; Kabanov, PORCID logo; Keller, C B; Kunzmann, M; Miller, A J; Mills, N T; O'Connell, B; Peters, S E; Planavsky, N J; Ritzer, S R; Schoepfer, S D; Wilby, P R; Yang, J
SourceGeochemical Perspectives Letters vol. 17, 2021 p. 21-26, https://doi.org/10.7185/geochemlet.2109 Open Access logo Open Access
Image
Year2021
Alt SeriesNatural Resources Canada, Contribution Series 20210075
PublisherEuropean Association of Geochemistry
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf; html
Subjectsgeochemistry; sedimentology; tectonics; environmental geology; Science and Technology; Nature and Environment; Archean; continental crust; tectonic history; geodynamics; volcanism; paleoclimates; bedrock geology; lithology; sedimentary rocks; weathering; weathering rates; bulk composition; major element geochemistry; silica; carbon dioxide; carbon geochemistry; Phanerozoic; Precambrian; Proterozoic
Illustrationsplots; tables; time series
ProgramGEM-GeoNorth: Geo-mapping for Energy and Minerals
Released2021 03 02
AbstractThe composition of continental crust records the balance between construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how igneous addition and chemical weathering have modified the continents' bulk composition are essential for understanding the evolution of geodynamics and climate. Using novel data analytic techniques we have extracted temporal trends in sediments' protolith composition and weathering intensity from the largest available compilation of sedimentary major element compositions: ~15,000 samples from 4.0 Ga to the present. 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 sequestered ~25 % more CO2 per mass eroded for the same weathering intensity than in subsequent time periods, consistent with carbon mass balance despite higher Archean outgassing rates and more limited continental exposure. Since 2.0 Ga, over long (>0.5 Gyr) timescales, crustal weathering intensity has remained relatively constant. On shorter timescales over the Phanerozoic, weathering intensity is correlated to global climate state, consistent with a weathering feedback acting in response to changes in CO2 sources or sinks.
Summary(Plain Language Summary, not published)
The composition of continental crust records the balance between construction by tectonics and destruction by physical and chemical erosion. Constraints on how addition from melted deep Earth and chemical weathering have modifed the continents' chemical composition are essential for understanding the evolution of geodynamics and climate. Using novel data-analytic techniques we have extracted temporal trends in the original composition of Earth's continental crust and weathering intensity from the largest available compilation of sedimentary major-element compositions: ~15,000 samples from 4.0 billion years ago (Gyr) to the present. 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 a long-term trend, the crustal weathering intensity has remained relatively constant since 2.0 Gyr. On shorter timescales over the Phanerozoic, weathering intensity is correlated to global climate state, through response of weathering to changes in CO2 sources or sinks.
GEOSCAN ID328335

 
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