Kinetic Models for Healing of the Subduction Interface Based on Observations of Ancient Accretionary Complexes

Abstract

Sand‐shale mélanges from the Kodiak accretionary complex and Shimanto belt of Japan record deformation during underthrusting along a paleosubduction interface in the range 150 to 350 °C. We use observations from these mélanges to construct a simple kinetic model that estimates the maximum time required to seal a single fracture as a measure of the rate of fault zone healing. Crack sealing involves diffusive redistribution of Si from mudstones with scaly fabric to undersaturated fluid‐filled cracks in sandstone blocks. Two driving forces are considered for the chemical potential gradient that drives crack sealing: (1) a transient drop in fluid pressure ∆Pf, and (2) a difference in mean stress between scaly slip surfaces in mudstones and cracks in stronger sandstone blocks. Sealing times are more sensitive to mean stress than ∆Pf, with up to four orders of magnitude faster sealing. Sealing durations are dependent on crack spacing, silica diffusion kinetics, and magnitude of the strength contrast between block and matrix, each of which is loosely constrained for conditions relevant to the seismogenic zone. We apply the model to three active subduction zones and find that sealing rates are fastest along Cascadia and several orders of magnitude slower for a given depth along Nicaragua and Tohoku slab‐top geotherms. The model provides (1) a framework for geochemical processes that influence subduction mechanics via crack sealing and shear fabric development and (2) demonstration that kinetically driven mass redistribution during the interseismic period is a plausible mechanism for creating asperities along smooth, sediment‐dominated convergent margins.

What’s down there? The structures, materials and environment of deep-seated slow slip and tremor

“…Recent kinetic models inspired by natural melange shear zones by Fisher et al . [ 237 ] examined the rates of diffusive redistribution of Si from melange matrix to blocks for two potential driving forces: (1) a transient drop in fluid pressure, and (2) a difference in mean stress between matrix and clasts. Their application of the model to geothermal gradients typical of subduction zones suggests minimum healing times of 10–100 years over the depth range corresponding to SST (approx.…”

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

“…The matrix consists of anastomosing slip surfaces that are frequently polished in hand‐samples and striated with slickenlines plunging down‐dip. These slip surfaces define a scaly fabric (Byrne, 1984; Cowan, 1982, 1985; Fisher, 1996; Fisher & Byrne, 1987; Fisher et al., 2019; Moore & Byrne, 1987; Moore et al., 1986; Vannucchi, 2019; Vannucchi et al., 2003) (Figures 3a–3c). Scaly fabric is concentrated in phyllosilicate‐rich lithologies that accommodate the majority of the shearing around the blocks.…”

Transient Slow Slip Characteristics of Frictional‐Viscous Subduction Megathrust Shear Zones

“…A more detailed analysis or comparison of recurrence intervals among model types is not appropriate here because the model setup tracks only the maximum velocity within the 2D model domain, whereas as noted in Section 3, near‐threshold and below‐threshold models commonly exhibit multiple events occurring simultaneously or in close succession. Additionally, in nature, event recurrence intervals are not only sensitive to plate boundary loading rates, but also to rates of fault healing (e.g., Fisher et al., 2019; Marone et al., 1995; McLaskey et al., 2012; Sibson, 1992), a poorly understood process that in our model framework would affect the time evolution of the state variable, but varying this parameter was beyond the scope of this study.…”