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Regulating continent growth and composition by chemical weathering

Proceedings of the National Academy of Sciences of the United States of America

By:
, , , , , ,
DOI: 10.1073/pnas.0711143105

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Abstract

Continents ride high above the ocean floor because they are underlain by thick, low-density, Si-rich, and Mg-poor crust. However, the parental magmas of continents were basaltic, which means they must have lost Mg relative to Si during their maturation into continents. Igneous differentiation followed by lower crustal delamination and chemical weathering followed by subduction recycling are possible solutions, but the relative magnitudes of each process have never been quantitatively constrained because of the lack of appropriate data. Here, we show that the relative contributions of these processes can be obtained by simultaneous examination of Mg and Li (an analog for Mg) on the regional and global scales in arcs, delaminated lower crust, and river waters. At least 20% of Mg is lost from continents by weathering, which translates into >20% of continental mass lost by weathering (40% by delamination). Chemical weathering leaves behind a more Si-rich and Mg-poor crust, which is less dense and hence decreases the probability of crustal recycling by subduction. Net continental growth is thus modulated by chemical weathering and likely influenced by secular changes in weathering mechanisms. ?? 2008 by The National Academy of Sciences of the USA.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Regulating continent growth and composition by chemical weathering
Series title:
Proceedings of the National Academy of Sciences of the United States of America
DOI:
10.1073/pnas.0711143105
Volume
105
Issue:
13
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
4981
Last page:
4986
Number of Pages:
6