Abstract

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Title:: Carbon Cycle Restrained Quantification of Weathering Depletion in Making Continental Crust

Author(s):: YANG Rui-yu; LI Gao-jun; CHEN Jun; Key Laboratory of Surficial Geochemistry of Ministry of Eductation, Nanjing University, Nanjing 210023, Jiangsu, China

Keywords:: element geochemistry; continental crust; continental weathering; carbon cycle; elemental mass balance; soluble element; mantle melting; andesitic composition

Abstract:: The cause leading to the andesitic composition of the continental crust is enigmatic. Soluble elements are leached out by chemical weathering from continents to oceans, and return to mantle through subduction, hence, continental weathering may be one possible explanation for the formation of andesitic continental crust. However, the contribution of weathering process remains difficult to be quantitatively constrained. As continental weathering is primarily controlled by p(CO₂), the deficit of continental weathering can be indirectly calculated by carbon cycle restraint. The two-stage mantle melting model proposed by Hofmann was used to constrain the primary composition of the continental crust; specifically, based on total continental calcite in sediments, and Mn, Fe, Mg, Na, P, Li, Sr corresponding to their molar ratios with Ca in weathering process following the elemental mass balance, the weathering fluxes were calculated. The results show that the depletion of the above 7 elements is consistent with their fluxes during weathering process, suggesting chemical weathering may have major impacts on the compositional evolution of the continental crust.