Quartz deposition and its influence on the deformation process of megathrusts in subduction zones

Abstract

We present a quantitative examination of the liberation and subsequent deposition of silica at the subduction zone plate interface in the Mugi mélange, an exhumed accretionary complex in the Shimanto Belt of southwest Japan. Frequency and thickness measurements indicate that mineralized veins hosted in deformed shales make up approximately 0.4% of the volume of this exposure. In addition, whole-rock geochemical evidence suggests that the net volume of SiO 2 liberated from the mélange at temperatures of < 200°C was as much as 35%, with up to 40% of the SiO 2 loss related to the smectite-illite (S-I) conversion reaction, and the rest attributable to the pressure solution of detrital quartz and feldspar. Kinetic modeling of the S-I reaction indicates active liberation of SiO 2 at approximately 70°C to 200°C, with peak SiO 2 loss at around 100°C, although these estimates should be slightly shifted toward lower temperature conditions based on X-ray diffraction (XRD) analyses of mixed-layer S-I in the Mugi mélange. The onset of pressure solution was not fully constrained, but has been documented to occur at around 150°C in the study area. The deposition in deformed shales of quartz liberated by pressure solution and the S-I reaction is probably linked to seismogenic behavior along the plate interface by (1) progressively enhanced velocity-weakening properties, which are favorable for unstable seismogenic faulting, including very-low-frequency earthquakes and (2) increasing intrinsic frictional strength, which leads to a step-down of the plate boundary décollement into oceanic basalt.

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

“…Furthermore, the reactivated fracture zones F6 and F7 [ Carton et al , ; Singh et al , ] and serpentinized upper mantle [ Qin and Singh , ] are present in this area; they may lead to hydrothermal circulation in the crust and upper mantle providing heat for the smectite‐illite transformation at the base of sediments. This dehydration transformation can supply SiO 2 at higher temperatures (70°C–200°C) [ Kameda et al , ], requiring some silica‐rich succession near the basement [ McNeill et al , ]. Our results show a large velocity drop caused by the HANP.…”

The accretion of foreland basin sediments during early stages of continental collision in the European Alps and similarities to accretionary wedge tectonics

“…Compared to earlier deformation stages, the liberation of fluids at this stage is rather negligible as indicated by the low values of Γ bulk (Figure a). At the same depths, however, pressure solution becomes active and causes together with the illite‐muscovite transformation the liberation and redistribution of SiO 2 , which is thought to facilitate a further embrittlement of the rocks and the change from a velocity‐strengthening to velocity‐weakening behavior [e.g., Moore et al , ; van de Kamp , ; Kameda et al , ]. We propose that this development is reflected by the onset of OOS‐thrusting at temperature >160°C and the brittle deformation that is recorded by the formation of quartz‐calcite veins in the study area (Figure b).…”

Alteration and dehydration of subducting oceanic crust within subduction zones: implications for décollement step-down and plate-boundary seismogenesis

“…Concurrently, the sedimentary décollement may be progressively hardened by ongoing quartz veining and/or cementation (Kameda et al 2014), a process that can cause a strength reversal and the fracturing and breakage of the basalt. This breakage will cause the fracture zone to propagate as a major thrust fault (i.e., a "step-down" of the décollement into the oceanic crust; Kimura and Ludden 1995;Ikesawa et al 2005), leading to underplating of the upper section of the oceanic crust and the incorporation of this material into the overriding accretionary prism.…”