Multiple generations of pseudotachylyte in the Wenchuan fault zone and their implications for coseismic weakening

Wang, Huan; Li, Haibing; Janssen, C.; Sun, Zhilei; Si, J.

doi:10.1016/j.jsg.2015.03.007

Cited by 26 publications

(34 citation statements)

References 57 publications

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“…Melt pseudotachylite has been discovered in the YBF zone, reflecting a 1100-1700°C frictional heating temperature achieved during earthquakes (Wang et al 2015); this might be localized in the principle slip zone of the fault. We understand that the temperatures estimated by the Raman spectra reflect regional metamorphism temperatures with no or slight influences of frictional heating.…”

Section: Origin Of Cms For the Cmvsmentioning

confidence: 98%

Origin and formation of carbonaceous material veins in the 2008 Wenchuan earthquake fault zone

Jiang

Zhang

et al. 2016

Earth Planet Sp

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This paper establishes a reference data set of carbonaceous materials (CMs) from the active fault zone of the Longmen Shan fault belt that ruptured in the 2008 Mw7.9 Wenchuan earthquake and presents an application of these data for studies of both other exhumed carbonaceous-rich fault zones and deep-drilling cores. The CMs distributed in the active fault zone are found as narrow veins and located along the slip surfaces. Microstructural observation shows that the carbonaceous material veins (CMVs) are located along slip surfaces in the fault gouge zones. Some CMVs have a cataclastic fabric, and their branches intrude into voids around the slip surfaces. Raman spectra of the CMVs show a wide (full width at half maximum >200 cm −1 ) D-peak at~1345 cm −1 (defect peak), which is much lower than the O-peak at~1595 cm −1 (ordered peak), indicating a metamorphic temperature of zeolite facies or lower than 250°C. In addition, the stable carbon isotopic compositions (δ 13 C values) of the CMVs, ranging from −23.4 to −26.4‰, are very similar to that of the kerogen collected from the Late Triassic Xujiahe Formation in Sichuan Basin. Given the data at which it may be formed, the Xujiahe Formation is the most likely origin of CMs for the CMVs, and it seems that some CMVs in the fault zone were crushed and intruded into the voids during coseismic events, possibly driven by an enhanced pore fluid pressure. Since graphitization is suggested as an indicator of transient frictional heating in this area, our study providing a reference data set of CMs would help future CM-rich fault-zone research to retrieve seismic signatures presumably occurring in the Longmen Shan fault zone belt.

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Section: Origin Of Cms For the Cmvsmentioning

confidence: 98%

Origin and formation of carbonaceous material veins in the 2008 Wenchuan earthquake fault zone

Jiang

Zhang

et al. 2016

Earth Planet Sp

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“…Results from the WFSD-1 cores and surface outcrop (Li et al 2013;Wang et al 2014Wang et al , 2015 show that the Yingxiu-Beichuan fault zone is about 200 m wide (thickness of the fault rocks) with individual fault gouge thicknesses ranging from 2 mm to ~4 m. The fault that ruptured during the Wenchuan earthquake along the Yingxiu-Beichuan fault zone is a high-angle thrust fault with a dip angle of 75°-65° from the surface to 600 m depth. For that fault segment, …”

Section: Wenchuan Earthquake Fault Structuresmentioning

confidence: 99%

Lithological and structural characterization of the Longmen Shan fault belt from the 3rd hole of the Wenchuan Earthquake Fault Scientific Drilling project (WFSD-3)

Wang

Yang

et al. 2015

Int J Earth Sci (Geol Rundsch)

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present in the hanging wall. The actual total thickness of the Guanxian-Anxian fault zone is ~210 m. Based on the analyses of comprehensive logging data, characteristics of the fault gouge, and seismic fault structures, the principal slip zone for the Wenchuan earthquake is identified in the black fault gouge at 1249.95 m depth in the cores, which lies almost at the bottom of the Guanxian-Anxian fault zone, and is also confirmed by surface rupture zone observations. The slip plane of the Wenchuan earthquake is a low-angle thrust fault with a dip angle of ~38° as estimated from the results of the WFSD-3 core analyses. The results from WFSD-1 showed that the Yingxiu-Beichuan segment is a high-angle thrust fault striking NW with a dip angle of ~65°. These two fault segments have different thicknesses and fault structures, which may suggest different faulting mechanisms and evolution history.

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“…(c) Geological cross sections of the Bajiaomiao profile; the long oblique lines are the lithologic boundaries. Figures a and b are reproduced exactly from Wang et al [].…”

Section: Pseudotachylyte In the Lsfbmentioning

confidence: 99%

“…(a) Typical microstructures of cataclasites with random fabrics, under plane‐polarized light; (b) and (c) recrystallized bulges with serrated and sutured grain boundaries (red arrows) in the large quartz porphyroclasts from the cataclasite/ultracataclasite, under cross‐polarized light; (d) microstructure of foliated cataclasite that indicates a thrust sense based on a S‐C fabric, under plane‐polarized light; (e) flow structure, under plane‐polarized light; (f) compound microlites in the dark matrix, under plane‐polarized light; (g and h) embayed quartz clast, under cross‐polarized light; (i and j) SEM images showing a typical melting flow structure that occurs at the edge of a quartz clast with an EDS spectra for the white cross spot in Figure j; and (g and h) SEM images showing honeycomb‐like structure in quartz. Figures i and j are reproduced exactly from Wang et al []. Abbreviation: Pst–pseudotachylyte, Cc–cataclasite, Mi–microlite, Qz–quartz.…”

Section: Pseudotachylyte In the Lsfbmentioning

confidence: 99%

“…As a direct product of frictional melting during large‐magnitude earthquakes, the existence of pseudotachylyte provides a new objective allowing study timing, location, and mechanism of the ancient coseismic faulting [ Sibson , ; Magloughlin and Spray , ; Lin , ]. Although there was controversy in the past years about the origin of the pseudotachylytes as a product of melting or a local comminution [ Sibson , ; Shimamoto and Nagahama , ], here careful observations in the studied outcrops at the central part of the YBF indicate that the pseudotachylytes were the result of frictional melting [ Wang et al ., ], and therefore, they are suitable for a geochronological study. Three different dating methods, stepwise‐heating 40 Ar/ 39 Ar of matrix glass, K‐Ar dating of the illite in the alteration phases, and ZFT applied to zircon grains separated from the pseudotachylyte veins, are used in this paper so that we could constrain the true age and crustal depth distribution of the ancient earthquakes in the YBF.…”

Section: Introductionmentioning

confidence: 99%

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New geochronology constraints on timing and depth of the ancient earthquakes along the Longmen Shan fault belt, eastern Tibet

Zheng

Sun

et al. 2016

Tectonics

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Pseudotachylyte is an ideal target to directly date ancient earthquake associated with regional faulting. Here we perform step‐heating 40Ar/39Ar, clay mineral K‐Ar, and zircon fission track (ZFT) analyses on the pseudotachylyte samples collected from the Yingxiu‐Beichuan coseismic rupture of the Longmen Shan fault belt (LSFB) to provide time constraints for the tectonic evolution of the LSFB during the Indosinian orogeny. 40Ar/39Ar results from the matrix show that the frictional melting occurred 226–235 Ma ago. Combined with mylonite dating of the host rock, the age of the ancient earthquakes is constrained at 231–238 Ma, with a formation depth of 10–14 km. As a response to the earthquakes, a series of soft‐sediment deformation structures are widely preserved in the Middle and Late Triassic strata along the Yingxiu‐Beichuan fault (YBF), indicating that the LSFB was seismically active since the Late Anisian and persisted episodically until the end of the Indosinian orogeny. Both clay mineral K‐Ar and ZFT analyses record a younger deformation or alteration with an age of approximately 195 Ma, corresponding to a postcollisional orogeny. These new data represent the first direct evidence of the regional thrusting (YBF) in the central LSFB during the Indosinian orogeny, concurrent with the initial ductile deformation of the western boundary fault. Tectonic inheritance then strongly influenced the evolution of the LSFB as most of the Mesozoic faults are reactivated by major Tertiary tectonic deformations.

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Multiple generations of pseudotachylyte in the Wenchuan fault zone and their implications for coseismic weakening

Cited by 26 publications

References 57 publications

Origin and formation of carbonaceous material veins in the 2008 Wenchuan earthquake fault zone

Origin and formation of carbonaceous material veins in the 2008 Wenchuan earthquake fault zone

Lithological and structural characterization of the Longmen Shan fault belt from the 3rd hole of the Wenchuan Earthquake Fault Scientific Drilling project (WFSD-3)

New geochronology constraints on timing and depth of the ancient earthquakes along the Longmen Shan fault belt, eastern Tibet

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