Generation Depth of the Pseudotachylyte from an Out-of-Sequence Thrust in Accretionary Prism &amp;ndash; Geothermobarometric Evidence

Okamoto, S.; Kimura, Gaku; Yamaguchi, Asuka; Yamaguchi, Hikoyuki; Kusuba, Yoko

doi:10.5194/sd-specialissue-47-2007

Cited by 10 publications

(3 citation statements)

References 6 publications

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“…Labels denote profiles as follow: (1) Hikurangi margin; (2) British Columbia; (3) Nankai; (4) Manila;(5) N. Honshu; (6) N. Sumatra; (7) N Kermadec; (8) which overlies (7) S. Kermadec; (9) Kamchatka; (for detailed locations seeEngland, 2018). Red circles show ambient P-T conditions for rocks from subduction settings in which pseudotachylytes have been reported(Andersen et al, 2014;Ikesawa et al, 2003;John & Schenk, 2006;Magott et al, 2016;Menant et al, 2018;Okamoto et al, 2007;Pittarello et al, 2022;Rowe et al, 2011;Vitale et al, 2019).…”

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confidence: 99%

Metamorphism and Deformation on Subduction Interfaces: 1. Physical Framework

England

Smye

2023

Geochem Geophys Geosyst

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A thermal and mechanical framework is presented for analysis of pressure‐temperature (P‐T) data and structural observations from high‐pressure‐low‐temperature (HPLT) terrains. P‐T data from 281 HPLT rocks exhibit two regimes separated at a pressure of ∼1.5 GPa, which corresponds to the modal maximum depth of thrust faulting in subduction zones. At pressures ≲1.5 GPa, interpreted as recording conditions on the plate interface, temperatures increase at about 350°C/GPa and are consistent with conditions calculated for shear stresses of ∼30–100 MPa on the interface. Such shear stresses are high enough to carry several kilometers' thickness of sediment at least to the base of the plate interface. Burial of material on plate interfaces occurs predominantly during large‐to‐great earthquakes; the exhumation phase involves contrasts in ascent rates of adjacent units, because of their differing buoyancies and strengths. In consequence, juxtaposition of unrelated rock types is expected to be ubiquitous, during both descent and ascent. The scarcity of temperatures higher than ∼650°C at pressures ≳1.5 GPa may reflect loss of material from the wedge‐slab interface by buoyant ascent. Exhumation of rocks in the subduction interface requires substantial reduction in shear stress, most plausibly by (near‐)cessation of subduction. During prograde metamorphism temperatures increase smoothly with depth in the plate interface, with almost isothermal compression in the wedge‐slab interface. Following cessation of subduction, rocks rising along the wedge‐slab interface are likely to heat slightly during decompression. Within the plate interface, temperatures drop following the cessation of shear heating, and rocks follow counter‐clockwise hairpin PT paths.

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Metamorphism and Deformation on Subduction Interfaces: 1. Physical Framework

England

Smye

2023

Geochem Geophys Geosyst

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“…The thrust is well exposed along the coast of Nobeoka city in Miyazaki Prefecture across the deeper Morotsuka and Kitagawa Groups (hanging wall) in the north and the shallower Hyuga Group (footwall) in the south (e.g. Kondo et al, 2005;Okamoto, Kimura, Takizawa, & Yamaguchi, 2006;Okamoto, Kimura, Yamaguchi, Yamaguchi, & Kusaba, 2007;Raimbourg, Shibata, Yamaguchi, Yamaguchi, & Kimura, 2009;Raimbourg et al, 2015). It is inferred to have been active from 48 Ma to 40 Ma (Hara & Kimura, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…In the vicinity of the fault core, brittle damage zones are distributed in the hanging wall and footwall with a thickness of from around 2 m to around 100 m, respectively, in the outcrop Kondo et al, 2005;Yamaguchi, Cox, Kimura, & Okamoto, 2011). Pseudotachylytes have been discovered in the brittle damage zones in the hanging wall, in which sharp faults and tension-crack veins coexist at high angles to the cleavage Kimura et al, 2013;Okamoto et al, 2006Okamoto et al, , 2007.…”

Section: Introductionmentioning

confidence: 99%

Physical property anisotropy of foliated fault rocks: Study from the Nobeoka Thrust, Shimanto Belt, southwest Japan

et al. 2018

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To investigate the physical property anisotropies of foliated fault rocks in subduction zones, the hanging wall phyllites and footwall cataclasites exhumed along the Nobeoka Thrust, a fossilized out‐of‐sequence‐thrust in the Shimanto Belt, Japan, was focused. Discrete physical property (electric resistivity, P‐ and S‐wave velocities, and porosity) measurements were conducted employing geologic coordinates (depth‐parallel direction, strike direction, and maximum dip direction of foliation), using the core samples obtained from the Nobeoka Thrust Drilling Project and compared the data to borehole geophysical logs. A higher sample P‐wave velocity (Vp), lower S‐wave velocity (Vs), higher Vp/Vs, and lower sample porosity and resistivity compared to the logs, are inferred to have been caused by the larger sampling scale of the logs and lower fluid saturation of the borehole. The phyllites and cataclasites exhibited substantial vertical and horizontal anisotropy of Vp (0.4–17.3 % and 2.7–13.8 %, respectively), Vs (0.5–56 % and 7.7–43 %, respectively), and resistivity (0.9–119 % and 2.0–65.9 %, respectively). The physical property anisotropies are primarily affected by the dip angles of foliation. The fault rocks that have gentler dip angles exhibit a higher Vp in the strike and maximum dip direction and a lower Vp in the depth‐parallel direction. In contrast, the fault rocks that have steeply dipping structures show a higher Vp in the strike and depth‐parallel directions with a lower velocity in the maximum dip direction. Resistivity anisotropy show a trend opposite to that of the Vp in relation to the dip angles. Our results show lower Vp anisotropy than those obtained in previous studies, which measured wave speeds perpendicular or parallel to foliation under confining pressure. This study highlights the significance of dip angles on vertical properties in geophysical surveys across foliated fault rocks.

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Contrasts in physical properties between the hanging wall and footwall of an exhumed seismogenic megasplay fault in a subduction zone—An example from the Nobeoka Thrust Drilling Project

Hamahashi

Saito

Kimura

et al. 2013

Geochem Geophys Geosyst

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[1] We examined the physical properties of an exhumed and fossilized subduction zone megasplay fault by analyzing geophysical logging data obtained by the Nobeoka Thrust Drilling Project, which provide a high-resolution transect of properties across the main fault zone. The footwall cataclasite exhibits higher averages of neutron porosity (7.6%) and lower values of electric resistivity (232 Xm) compared to the hanging wall phyllite (4.8%, 453 Xm). This clear contrast between the hanging wall and footwall may account for the difference in maximum burial and structural variation. Despite the contrast observed between the hanging wall and footwall in macroscopic scale, the resistivity and porosity data from both the hanging wall and footwall can be fit with a single curve using Archie's law, suggesting the similarities in microstructures and mineralogy in this low porosity range. Above the main fault core of the Nobeoka Thrust a brittle damage zone in the hanging wall contains pseudotachylyte as evidence of the seismogenic slip and does not follow Archie's law. Damage zones in the hanging wall are also observed in the modern splay fault at shallow depth in the Nankai Trough but with much thicker width, whereas the footwall damage zone is more extensive in the Nobeoka Thrust. Splay faults may exhibit strong deformation in the hanging wall in the early stage, and as fault rocks get buried deeper and as displacement and physical property contrast increase across the fault, the damage effect may eventually be enlarged in the footwall.

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Generation Depth of the Pseudotachylyte from an Out-of-Sequence Thrust in Accretionary Prism – Geothermobarometric Evidence

Abstract: No abstract available. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.s01.41.2007" target="_blank">10.2204/iodp.sd.s01.41.2007</a>

Cited by 10 publications

References 6 publications

Metamorphism and Deformation on Subduction Interfaces: 1. Physical Framework

Metamorphism and Deformation on Subduction Interfaces: 1. Physical Framework

Physical property anisotropy of foliated fault rocks: Study from the Nobeoka Thrust, Shimanto Belt, southwest Japan

Contrasts in physical properties between the hanging wall and footwall of an exhumed seismogenic megasplay fault in a subduction zone—An example from the Nobeoka Thrust Drilling Project

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