Underlying mechanism of the great thickness of granite weathering crust: Reduction of ridge erosion via coarse quartz particles

Abstract

The deep weathering crust of granite is widely distributed globally, and its elevation and thickness are directly affected by ridge erosion, the extent of which is not well understood. In this study, the behaviors, including the enrichment coefficient, content, of coarse quartz particles on the surfaces of typical granitic weathering crusts in Wuhua County and Meixian County (Guangdong Province, China) were investigated. Coarse quartz particles (>5 mm) were selected based on the enrichment factor for conducting splash erosion and weathering experiments. The rates of splash erosion and weathering for these particles were quantified under natural conditions. Moreover, a model was established to estimate splash erosion on ridge. Specifically, quartz particles with sizes of > 5 mm were found to have the smallest splash erosion amount and the largest enrichment coefficient. Thus, these particles were used for the estimation of the splash erosion of ridges. Model calculations revealed recent average annual erosion thicknesses of 1.57 mm and 1.31 mm on ridges enriched with coarse quartz particles in Wuhua and Meixian Counties, respectively, whereas a greater value of 5.56 mm was estimated on ridges without coarse quartz particles but with the plant age and root exposure height conditions. Moreover, in the Pinus massoniana forest in Wuhua County, the erosion intensity value of the ridges without the coarse quartz particles is calculated to be 7.62 times greater than that of the ridges with coarse quartz particles (0.73 mm). These results indicated that coarse quartz particles could effectively reduce the erosion of the weathering crust and form a deep granite weathering crust. These results could enhance the understanding of the stability of deep granite weathering crusts.