Insights from the geological record of deformation along the subduction interface at depths of seismogenesis

Abstract

Subduction interfaces are loci of interdependent seismic slip behavior, fluid flow, and mineral redistribution. Mineral redistribution leads to coupling between fluid flow and slip behavior through decreases in porosity/permeability and increases in cohesion during the interseismic period. We investigate this system from the perspective of ancient accretionary complexes with regional zones of mélange that record noncoaxial strain during underthrusting adjacent to the subduction interface. Deformation of weak mudstones is accompanied by low-grade metamorphic reactions, dissolution along scaly microfaults, and the removal of fluid-mobile chemical components, whereas stronger sandstone blocks preserve veins that contain chemical components depleted in mudstones. These observations support local diffusive mass transport from scaly fabrics to veins during interseismic viscous coupling. Underthrusting sediments record a crack porosity that fluctuates due to the interplay of cracking and precipitation. Permanent interseismic deformation involves pressure solution slip, strain hardening, and the development of new shears in undeformed material. In contrast, coseismic slip may be accommodated within observed narrow zones of cataclastic deformation at the top of many mélange terranes. A kinetic model implies interseismic changes in physical properties in less than hundreds of years, and a numerical model that couples an earthquake simulator with a fluid flow system depicts a subduction zone interface governed by feedbacks between fluid production, permeability, hydrofracturing, and aging via mineral precipitation. During an earthquake, interseismic permeability reduction is followed by coseismic rupture of low permeability seals and fluid pressure drop in the seismogenic zone. Updip of the seismogenic zone, there is a post-seismic wave of higher fluid pressure that propagates trenchward.

Geological records of transient fluid drainage into the shallow mantle wedge

“…S4, A and B) ( 55 ) in the Atg-Ctl veins suggests that each vein resulted from a single fluid flow event. In addition, it indicates that an open fracture persisted until mineral precipitation filled the fractue ( 56 ). This fluid could have been at higher temperatures (Atg-Brc equilibrium) than the host rock in which Lz-Brc was stable, although the precise temperature difference is not clear.…”

Quantifying Interseismic Volume Strain from Chemical Mass‐Balance Analysis in Tectonic Mélanges

“…For the Makimine mélange, which has subducted to the base of the seismogenic zone, these fluid sources are absent. Fisher et al (2021) employed a numerical model developed by Hooker and Fisher (2021), which considered the negative feedback between the dissolution-precipitation process and permeability along plate interfaces and demonstrated a post-seismic updip migration of fluid due to the rupture of seals resulting from the diffusive mass transfer process. This allows the fluid generated by the dehydration of subducted oceanic crusts at depth to transport upward, which likely explains the large amount of external fluid required for the additional deposition of veins observed in our analysis.…”

“…Some veins consist of both quartz and calcite, with calcite grains preserved in the middle and quartz grains grown on both sides of the veins (Figure 5b). Albite and chlorite are also found in veins of several mélange units (e.g., Fisher et al., 2021; Ramirez et al., 2021).…”

“…These mélanges are interpreted as damage zones at the footwall of paleodécollements or regional out‐of‐sequence thrusts (e.g., Fisher & Byrne, 1987), given the presence of cm‐scale zones of cataclastic rocks on top of them (e.g., Hashimoto et al., 2012; Ikesawa et al., 2003; Kitamura et al., 2005; Meneghini et al., 2010). During interseismic periods, plate motion is likely accommodated by diffusive mass transfer strain across 10–100‐m‐wide mélange zones, while coseismic slip occurs within narrow cataclasites (Fisher et al., 2021). Thus, exhumed mélange rocks provide unique materials for directly observing the interseismic deformation accumulating in subduction fault zones.…”

Computing Rates and Distributions of Rock Recovery in Subduction Zones

“…Fortunately, clues about the nature and PT limits of rock recovery are provided by many extensively studied examples of exhumed subduction interfaces (e.g., Agard et al., 2018; Angiboust et al., 2011, 2015; Cloos & Shreve, 1988; Fisher et al., 2021; Ioannidi et al., 2020; Kitamura & Kimura, 2012; Kotowski & Behr, 2019; Locatelli et al., 2019; Monié & Agard, 2009; Okay, 1989; Platt, 1986; Plunder et al., 2013, 2015; Tewksbury‐Christle et al., 2021; Wakabayashi, 2015). However, these type localities represent an unknown fraction of subducted material and differ significantly in terms of their geometry (field relationships), composition (rock types), and interpreted deformation histories (both detachment and exhumation).…”