Isovolumetric geochemical investigation of a buried granite saprolite near Columbia,SC, U.S.A. |
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| Authors: | LR Gardner I Kheoruenromne HS Chen |
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| Institution: | Department of Geology, University of South Carolina, Columbia, SC 29208, U.S.A. |
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| Abstract: | Saprolites are residual soils which preserve the textures of their parent rocks and thus have evolved by an isovolumetric process of weathering (MILLOT, 1970, The Geology of Clays, Springer). Using bulk density, saprolite elemental analyses can be converted to units of g cm?3. Furthermore, an empirical reaction progress diagram can be constructed for a suite of saprolite samples by plotting element concentrations (in g cm?3) against bulk density (B.D.). Our data for a granite saprolite show that Al2O3 and SiO2 decrease in a linear fashion from B.D. 2.1g cm?3 to 1.5g cm?3 but that K2O follows a curvilinear trend such that it decreases from 75% of its fresh rock value at B.D. 1.6 g cm?3 to nearly zero at B.D. 1.5 g cm?3. The only hypothetical reaction paths that are compatible with these B.D. vs A12O3, SiO2 and K2O constraints are those in which orthoclase alters to kaolinite through an intermediate potassium phase similar to KAl3Si3O10(OH)2 or KAl2Si2O6(OH)3 (hypothetical K-kaolinite). Normative mineral calculations, X-ray diffraction data and structural H2O data are employed to test this conclusion. |
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