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Comparisons of short-term and long-term chemical weathering rates in granitoid regoliths

Arthur F. White and David A. Stonestrom

U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA, 94025-3591, USA


Chemical weathering rates in three deeply weathered granitoid profiles are evaluated based on SiO2 fluxes. Aqueous fluxes below the zone of seasonal variations are estimated from mean-annual pore-water SiO2 concentrations of 0.1 to 1.5 mM and average hydraulic-flux densities of 6 x 10 -9 to 14 x 10 -9 m s - 1 for quasi-steady state portions of the profiles. Corresponding fluid-residence times in the profiles ranged from 10 to 44 years. Total solid state SiO2 losses, based on chemical and volumetric changes, ranged from 19 to 110 kmoles SiO2 m- 2 as a result of 200 to 375 ka of chemical weathering. Extrapolation of contemporary solute fluxes to comparable time periods reproduced SiO2 losses to about an order of magnitude. A strong positive correlation exists between moisture content and rates of chemical weathering.

A.F.White & D.A.Stonestrom, 1998, Comparisons of short-term and long-term chemical weathering rates in granitoid regoliths, in Arehart, G.B., and Hulston, J.R., eds., Proceedings of the 9th International Symposium on Water-Rock Interaction, WRI-9, Taupo, New Zealand, March 30-April 3, 1998, p. 399-402.

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