High- and low-stress subduction zones recognized in the rock record

Ishii, Kazuhiko; Wallis, Simon

doi:10.1016/j.epsl.2019.115935

Cited by 15 publications

(14 citation statements)

References 46 publications

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“…A comparison with the calculated thermal structure of the Sanbagawa metamorphic belt proposed in previous studies (Aoya & Endo, 2017; Aoya et al., 2009; Ishii & Wallis, 2020) suggests the temperature discontinuity at ~400°C or slightly higher coincides closely with the region where the slab is in contact with the continental Moho. The Sanbagawa metamorphic belt is an example of warm subduction and a close analogue for modern subduction in SW Japan where the temperature of the slab at the Moho depth is also estimated to be ~400°C (Peacock, 2009).…”

Section: Discussionsupporting

confidence: 61%

Thermal structure in subducted units from continental Moho depths in a palaeo subduction zone, the Asemigawa region of the Sanbagawa metamorphic belt, SW Japan

Kouketsu

Sadamoto

Umeda

et al. 2021

Journal Metamorphic Geology

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Raman CM geothermometry applied to 126 samples of pelitic schists collected over an area of 11 km × 7 km reveals the thermal structure of the Asemigawa region of the Sanbagawa metamorphic belt, southwest Japan in unprecedented detail. In general, the estimated temperatures gradually increase from south to north in the range of 288-553°C. However, a temperature gap from ~380 to ~440°C is identified near the boundary between the chlorite and garnet zones. This temperature region matches the depth of the continental Moho of the Sanbagawa subduction zone. The temperature gradient in the higher-temperature domain is higher than that in the lowertemperature domain, and large-scale tight folds that affect the thermal structure are developed in the high-grade units and in the vicinity of the temperature discontinuity.These geological structures probably reflect that the exhumed slab units was dammed at the Moho depth due to the upward movement being impeded by increase in the coupling strength of the overlying rocks associated with exhumation from beneath serpentinite rocks to a shallower domain overlain by crustal rocks. Changes in the coupling strength along the subduction boundary led the strong folding at the highertemperature domain and the pre-formed foliation developed at the Moho depth may have acted as the tectonic boundary, resulting in a temperature discontinuity. These results will contribute to elucidating various geological phenomena occurring in the forearc regions of modern subduction zones. K E Y W O R D Scontinental Moho, Raman carbonaceous material geothermometer, Sanbagawa (Sambagawa) metamorphic belt, slow earthquake, thermal structure

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Section: Discussionsupporting

confidence: 61%

Thermal structure in subducted units from continental Moho depths in a palaeo subduction zone, the Asemigawa region of the Sanbagawa metamorphic belt, SW Japan

Kouketsu

Sadamoto

Umeda

et al. 2021

Journal Metamorphic Geology

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“…The Sanbagawa belt of southwest Japan is a Cretaceous subduction‐type metamorphic belt (Wallis & Okudaira, 2016) and estimates of P–T conditions have played an important role in examining the importance of different tectonic models for the subduction history of Southwest Japan (Aoya et al, 2003; Ishii & Wallis, 2020; Iwamori, 2000; Uehara & Aoya, 2005). The metamorphic grade shows general south to north increase and the northern part of the Sanbagawa belt is bounded by a large‐scale dominantly strike‐slip fault, the median tectonic line (MTL).…”

Section: Introductionmentioning

confidence: 99%

Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources

Yamaoka

Wallis

2022

Island Arc

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Application of Raman spectroscopy of carbonaceous material thermometry to samples of metasedimentary rock from the low‐grade Sanbagawa belt in the central Kii peninsula reveals a progressive decrease in temperature from ~390 °C close to the northern boundary, a major continental shear zone—the median tectonic line (MTL)—to ~270 °C and ~7 km to the south and roughly constant temperature distribution thereafter. Within the Sanbagawa belt, the thermal structure is not significantly modified by slip‐on fault boundaries between different geological units or folding. Meso‐ and microstructural observations combined with strain analysis using detrital grains in meta‐mudstone indicate a similar deformation history throughout the area and no correlation between ductile strain and temperature gradients. These observations suggest the observed thermal structure was developed after the main stages of ductile deformation of the Sanbagawa belt were complete and are not due to localized preferential exhumation along with the MTL. The observations also require a heat source along with the MTL. Order of magnitude estimates suggest the influx of warm fluid along the MTL are viable causes of the observed thermal anomaly. Although shear heating would be another possible explanation, thermal calculations require anomalous fast slip rates along the MTL and much greater frictional strength than generally considered reasonable. For these reasons, fluid infiltration is our preferred model.

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“…In addition, the transition from continental subduction to collision could lead to heat overprinting and result in re‐equilibration at higher geothermal gradients (e.g., Bousquet et al., 2008; Soret et al., 2021), which may cause the calculated temperature at peak pressure higher than the true value (Faryad & Cuthbert, 2020). For the second case, analytical and numerical modeling demonstrated that change of shear heating induced by lithological strength and subduction velocity could significantly influence the value and shape of the thermal gradient for continental subduction zones, with larger shear stress along subduction interface producing higher temperature at a specific pressure and more concave upward P – T curves (e.g., Ishii & Wallis, 2020; Kohn et al., 2018; Peacock, 1995). The nature of the overriding plate may also exert some effects on the thermal structure of the continental subduction zone, as some metamorphic rocks produced by subduction of the continental lithosphere under magmatic arc recorded higher geothermal gradients (e.g., Agard & Vitale‐Brovarone, 2013).…”

Section: Discussionmentioning

confidence: 99%

Thermal Structure of the Paleo‐Continental Subduction Zone: Insights From Quantitatively Constrained Prograde P–T Paths of Exhumed LT/UHP Eclogites in the Dabie Orogen

Xia

Zhang

Gao

2023

Geochem Geophys Geosyst

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The discrepancy of geothermal gradients predicted by numerical modeling and recorded by peak metamorphic conditions of exhumed high/ultrahigh pressure (HP/UHP) metamorphic rocks triggers many uncertainties on the thermal structure of subduction zones, which is especially significant for continental subduction zones. Well‐constrained prograde P‒temperature (T) paths of HP/UHP rocks reflect the change in P–T conditions during continental subduction and are insusceptible to later processes, making them robust recorders of the thermal structure of subduction zones. To make a reliable estimation of the thermal structure of a continental subduction zone, the prograde P–T paths of three low (L)T‒UHP eclogites in the Dabie orogen were robustly constrained using a multiple thermobarometry method. The results demonstrate that these eclogites underwent three stages of metamorphic evolution during continental subduction from epidote amphibolite‐facies at ∼450°C–470°C/11–13 kbar, through amphibole eclogite‐facies at 585°C–600°C/17–19 kbar, to peak UHP eclogite‐facies at 600°C–630°C/27–29 kbar, indicating a low and continuously changing geothermal gradient from ∼12°C/km at lower crust depth (40 km) to 10°C/km at depth of 60 km and to ∼6°C/km at sub‐arc depth (100 km). The consistency of this result and the average thermal gradient recovered by peak metamorphic conditions of exhumed HP/UHP metamorphic rocks of continental origin suggests that the continental subduction zones may have a common thermal structure characterized by strongly concave upward geothermal gradient. A comparison of the results of this study and analytical models shows that shear heating may play a crucial role in the thermal evolution of continental subduction zones.

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High- and low-stress subduction zones recognized in the rock record

Cited by 15 publications

References 46 publications

Thermal structure in subducted units from continental Moho depths in a palaeo subduction zone, the Asemigawa region of the Sanbagawa metamorphic belt, SW Japan

Thermal structure in subducted units from continental Moho depths in a palaeo subduction zone, the Asemigawa region of the Sanbagawa metamorphic belt, SW Japan

Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources

Thermal Structure of the Paleo‐Continental Subduction Zone: Insights From Quantitatively Constrained Prograde P–T Paths of Exhumed LT/UHP Eclogites in the Dabie Orogen

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