The time dependency of silicate mineral weathering has been explored in the literature in terms of processes and features that are intrinsic and extrinsic to the mineral [1]. However, although the advent of sophisticated reactive transport models has allowed for coupling increasingly complex reaction and transport processes [2,3], a simple and fundamental understanding of the temporal evolution of weathering is lacking. Here, we propose that a purely deterministic approach may not be sufficient given the inherent differences in reactivity over space and time. Therefore, we explore how a combined reaction-diffusion and random rate model – informed by a stochastic distribution of weathering rates K (T^-1) – might be able to explain not only the temporal evolution but also the hydrodynamics of weathering during earthquakes; the latter being purportedly described by time-dependent property permeability (L²). Preliminary model results show that (1) an increase in dimensionless quantity βr_p, where β is the diffusion length (L^-1) and r_p is the distance between pores (L), leads to a decrease in minimum reaction rate with time from the relation K_min ∝ e^-βrp/r_p ; (2) at a given porosity, a time-dependent decrease in reactivity arises as permeability decreases due to decreasing pore size (and therefore increasing r_p), which in turn may be related to the time-dependent feedback between dissolution and precipitation; (3) while permeability is lower in older soils, transient stresses as during earthquakes [4], may induce more efficient "declogging" of pores in these soils than in younger soils due to higher hydrodynamic viscous shear stress, thereby, resulting in a coseismic change in stream discharge Q; and (4) subsequent weathering beyond t~K_min^-1 exhibits a fall in rates, marking the cessation of logarithmic decay possibly due to dissolution-precipitation feedback.

[1] White and Brantley (2003), Chem. Geol. 202, 479.

[2] Lichtner P.C. (1996), Mineralogical Society of America, 1-81.

[3] Maher K., Steefel C.I., White A.F. and Stonestrom D.A. (2009), Geochim. Cosmochim. Acta 73, 2804-2831.

[4] Manga M., Beresnev I., Brodsky E. E., Elkhoury J. E., Elsworth D., Ingebritsen S. E., Mays D.C., and Wang C.Y. (2012), Rev. Geophys., 50, RG2004.