Soil profiles as indicators of mineral weathering rates and organic interactions for a Pennsylvania diabase

Abstract

Basaltic bedrock dissolves quickly, and its weathering rate is therefore important towards controlling the composition of natural waters, soil formation, and CO2 concentrations in the atmosphere. Despite its importance, however, few reports of basalt or diabase and gabbro weathering rates exist in the literature, and most have been measured in laboratory dissolution experiments or based on watershed studies. Here, using elemental profiles measured through regolith on a Jurassic diabase dike in south-central Pennsylvania, we calculate time-integrated log dissolution rates (molm−2s−1) of the primary minerals plagioclase (−14.9s−1) and augite (−14.8), and of smectite (−17.6), a secondary clay mineral formed in the soil. Characteristic patterns in elemental profiles are consistent with preserved signatures of corestone formation. Elemental and mineral signatures of the soils relative to the parent rock are compared to predictions from citrate-containing basalt column dissolution experiments. Depletion of apatite and of Al, Fe, Mn, Ti, P, Y, Ni, Cr, Sc, V, Ga, Cu, Zn, and La are observed in the upper meter of the profile relative to the parent rock.