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

Pure lithium hexafluorophosphate (LiPF6) was successfully prepared at room temperature (23 °C) by introducing fluorine gas into a reactor containing LiF and P at −196 °C. The mass fractions of LiPF6 and LiF in products prepared at 23 °C were 1.00 and 0.00, respectively, by means of XRD-Rietveld analysis. Namely, the prepared LiPF6 was pure enough to be used as an electrolyte salt in lithium ion batteries.

A Raman geothermometer, which utilizes the degree of graphitization of carbonaceous material, has been widely applied to estimate the recrystallization temperature of metapelite. This study evaluates the degree of graphitization of carbonaceous material, which is affected by several factors, and tests the robustness of the Raman carbonaceous material geothermometer defined by the R2 [= D1/(G + D1 + D2) area ratio] value. The main results are as follows. (1) Laser radiation over 6 mW at the sample surface caused a significant decrease in the R2 value, owing to the local increase in surface temperature of the carbonaceous material, and thus gave an overestimation of the recrystallization temperature. On the contrary, laser irradiation of 2 mW showed no distinct alteration of the spectrum during continuous analyses up to 120 s. (2) Carbonaceous materials occurring as matrix and inclusion phases in silicate minerals in a thin section showed no significant difference in R2 value. (3) The average R2 value of 10 samples collected from an outcrop at a scale of 2-3 m was 0.483 ± 0.012, corresponding to a temperature of 416 ± 5°C. This result implies that an arbitrary sample can likely represent the R2 value of the entire outcrop from which the sample was collected. (4) No distinct alteration of the R2 value around a shear zone width of 1-1.5 m was measured in the metapelites. The degree of graphitization of carbonaceous material was not noticeably altered by deformation during exhumation and local fracturing. Moreover, the Raman analysis of the carbonaceous material under the appropriate laser power condition can estimate the peak metamorphic temperature of rocks regardless of scale from thin section to outcrop.