Mobilization of Al and Ti during weathering — Isovolumetric geochemical evidence

Abstract

Variations in the volumetric concentrations of Al2O3 and TiO2 (in g cm−3) as a function of bulk density for 18 different saprolite suites strongly suggest that significant mobilization of Al and Ti during weathering is more common than is generally assumed. Although trends of decreasing Al2O3 (in g cm−3) with decreasing bulk density could result from dilation, textural and structural features in saprolites argue against significant volume expansion during weathering. Indeed it appears from theoretical calculations that most weathering reactions, including those in which Al is conserved, remove large quantities of various oxides and in the process should create significant amounts of void space. Accordingly, unless large quantities of smectite are produced, it seems unlikely that expansive forces should arise from such reactions. Theoretical calculations are presented that show the effect of dilation on reaction paths. Such calculations are shown to be useful in evaluating the impact of dilation (or compaction) in cases where textural and/or structural criteria are unavailable or ambiguous. © 1980, All rights reserved.