Major Element Composition of Sediments in Terms of Weathering and Provenance: Implications for Crustal Recycling


Type
Article
Change log
Abstract

jats:titleAbstract</jats:title>jats:pThe elemental composition of a sediment is set by the composition of its protolith and modified by weathering, sorting, and diagenesis. An important problem is deconvolving these contributions to a sediment's composition to arrive at information about processes that operate on the Earth's surface. We approach this problem by developing a predictive and invertible model of sedimentary major element composition. We compile a data set of sedimentary rock, river sediment, soil, and igneous rock compositions. Principal component analysis of the data set shows that most variation can be simplified to a small number of variables. We thus show that any sediment's composition can be described with just two vectors of igneous evolution and weathering. We hence define a model for sedimentary composition as a combination of these processes. A 1:1 correspondence is observed between predictions and independent data. The log ratios<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/ggge22195-math-0001.png" xlink:title="urn:x-wiley:ggge:media:ggge22195:ggge22195-math-0001" />and<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/ggge22195-math-0002.png" xlink:title="urn:x-wiley:ggge:media:ggge22195:ggge22195-math-0002" />are found to be simple proxies for, respectively, the model's protolith and weathering indices. Significant deviations from the model can be explained by sodium‐calcium exchange. Using this approach, we show that the major element composition of the upper continental crust has been modified by weathering, and we calculate the amount of each element that it must have lost to modify it to its present composition. By extrapolating modern weathering rates over the age of the crust, we conclude that it has not retained a significant amount of the necessarily produced weathering restite. This restite has likely been subducted into the mantle, indicating a crust‐to‐mantle recycling rate of 1.33 ± 0.89 ×10jats:sup13</jats:sup> kg·yearjats:sup−1</jats:sup>.</jats:p>

Description
Keywords
chemical weathering, composition of the continents, provenance, crustal recycling, compositional data analysis, sediment geochemistry
Journal Title
Geochemistry, Geophysics, Geosystems
Conference Name
Journal ISSN
1525-2027
1525-2027
Volume Title
21
Publisher
American Geophysical Union (AGU)
Rights
All rights reserved