The Influence of Climate and Topography on the Composition of Modern Pluton-derived Sand

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This project will attempt to quantify the influence of temperature, precipitation, slope gradient and azimuth on the nature, rate and products of weathering of granitic rocks. The dependent variables examined are the change in modal mineralogy and bulk chemistry when the parent rock disintegrates to sand- sized material, and the survivability of mineral-mineral interfaces in sand-sized rock fragments within the weathered grus. The independent variables are mean annual precipitation, mean annual temperature, temperature-weighted precipitation, and the mean gradient and azimuth of the slopes on which weathering takes place. Five lithologically identical plutons in diverse climatic settings have been chosen for study, which allow the pair-wise comparison of weathering settings in which four of the 5 independent variables can be held constant, while the fifth attains high and low values in the two members of the pair. The analysis of interface survival encompasses stereologic analytic methods that have never been applied to sedimentary petrography before and a new conceptual framework for viewing the rock fragment population of sands. Potential exists for the development of lithological indicators of past climatic change.