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

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 so...

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Bibliographic Details
Published in:Journal of metamorphic geology 2021-08, Vol.39 (6), p.727-749
Main Authors: Kouketsu, Yui, Sadamoto, Kazushi, Umeda, Hayato, Kawahara, Hirokazu, Nagaya, Takayoshi, Taguchi, Tomoki, Mori, Hiroshi, Wallis, Simon, Enami, Masaki
Format: Article
Language:English
Subjects:
Belts
Chlorite
continental Moho
Coupling
Depth
Discontinuity
Domains
Garnet
Geological structures
Moho
Raman carbonaceous material geothermometer
Rock
Rocks
Sanbagawa (Sambagawa) metamorphic belt
Schists
Serpentinite
slow earthquake
Subduction
Subduction (geology)
Subduction zones
Tectonics
Temperature gradients
Thermal structure
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Summary: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 lower‐temperature 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 higher‐temperature 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.
ISSN:0263-4929
1525-1314
DOI:10.1111/jmg.12584