P-T conditions of cataclastic deformation associated with underplating: An example from the Cretaceous Shimanto complex, Kii Peninsula, SW Japan

Abstract

P-T conditions of cataclastic deformation associated with underplating in subduction zone are estimated from fluid inclusions within the post-mélange veins in the Cretaceous Shimanto Belt, Kii Peninsula, SW Japan. Both cataclasite and post-mélange veins cut the mélange fabric and are distributed along the thrusts in duplex structure. The homogenization temperatures range from 200 (±10)• C to 270 (±42)• C corresponding to entrapment pressures over a wide range from 145 (±5) MPa to 304 (−20) MPa. Our results have important implications in evaluating the relationship between underplating processes by duplexing and coseismic deformation in accretionary complexes.

Tectonolithification of sandstone prior to the onset of seismogenic subduction zone: Evidence from tectonic mélange of the Shimanto Belt, Japan

“…Geological studies of on-land tectonic mélange have shown that sandstones are finely broken [e.g., Cowan, 1982;Byrne, 1984;Agar, 1990]. Although the mechanical behavior of sandstone has been well studied by many experiments [e.g., Zhang et al, 1990aZhang et al, , 1990bMarone et al, 1990;Wong et al, 1997], quantitative evaluation of the deformation conditions are sparse, except for some inferences on the P-T conditions [Vrolijk, 1987;Hashimoto et al, 2002Hashimoto et al, , 2003Lewis and Byrne, 2003;Matsumura et al, 2003]. Constraining the deformation and lithification process of sandstone is therefore one of the keys to understanding the onset of the seismogenic zone.…”

Geological evidence for shallow ductile-brittle transition zones along subduction interfaces: example from the Shimanto Belt, SW Japan

“…No systematic variation in homogenization temperatures from calcite hosts has been noted suggesting that the constant density assumption for the trapped fluids is valid (e.g., Roedder, 1984). (Hashimoto et al, 2002Matsumura et al, 2003;Hashimoto et al, 2012). Although the data are limited, the pressuretemperature condition for the Mugi mélange tends to shift to a higher thermal gradient, possibly because of the relatively young and hot plate subduction (Matsumura et al, 2003).…”

“…Pressure-temperature conditions for the formations of the extension and the shear veins have been previously estimated on the basis of fluid inclusion analysis from three mélange zones in the Cretaceous Shimanto Belt: the Mugi mélange (Matsumura et al, 2003), the Miyama formation (Hashimoto et al, 2002, and the Yokonami mélange (Hashimoto et al, 2012) (see locations in Figure 1). For the Yokonami mélange, the pressure-temperature condition only for the shear veins was obtained.…”

“…Therefore, the overlapping Figure 4 Pressure-temperature conditions for extension vein and shear vein formation. (A) Pressure-temperature conditions for extension vein and shear vein formation for the Mugi mélange (Matsumura et al, 2003), Miyama mélange (Hashimoto et al, 2002, and Yokonami mélange (Hashimoto et al, 2012) (locations are shown in Figure 1 area in temperature conditions can be regarded as the shallow ductile-brittle transition zone from the ductile mélange matrix to brittle shear veins. Because the slab age is comparable in the Yokonami mélange and the Miyama formation, the temperature range of the ductile-brittle transition zone is constrained by the data from the Yokonami mélange and the Miyama formation.…”

“…The spatiotemporal relation between plastic and brittle deformations, however, has been expressed as deformations in a heterogeneous mélange rheology (e.g., Fagereng and Sibson, 2010). Extension veins related to mélange fabrics and shear veins cutting the mélange fabrics have been well documented, with detailed pressure-temperature conditions from the Mugi mélange, Miyama formation, and Yokonami mélange in the Cretaceous Shimanto Belt (e.g., Hashimoto et al, 2002Hashimoto et al, , 2003Matsumura et al, 2003;Hashimoto et al, 2012) (see locations in Figure 1); these data can be a key in understanding the relation between ductile deformation for mélange and brittle failure (shear veins) in lithified shale matrices. In this study, we summarize the differences between observed deformation features and inferred deformation mechanisms for ductile mélange and shear vein formations in detail, with reference to published pressuretemperature conditions.…”