Rock-based measurement of temperature-dependent plagioclase weathering

Long-term ( > 10⁵ years) weathering can be quantified by measuring microsopic dissolution of minerals in exposed rock surfaces. Digital backscattered (BSE) electron microscope images of plagioclase porosity in field exposures of known age resolves weathering at finer scales and over longer time spans than conventional solute budget and laboratory studies. Rock-based BSE imaging is therefore a potentially useful tool for quantifying steady-state weathering fluxes occurring over geologic time. Here, we compare results of the rock-based method against solute-budget and experimental data, using plagioclase weathering rates from ¹⁴C-dated basalt flows on Hualalai Volcano in Hawaii, USA. A rock-based field activation energy of 26.2 kcal mol^-1 is somewhat higher than solute-budget and laboratory measurements of plagioclase weathering.