Thermal structure of the Kebara Formation and its proximal areas in the western Kii Peninsula, SW Japan: Application of the carbonaceous material Raman geothermometry

Peak metamorphic temperature of the Nishisonogi unit of the Nagasaki Metamorphic Rocks, western Kyushu, Japan

“…However, the thermal structure of the Nishisonogi unit remains poorly understood because the mineral assemblages are typically unsuitable for thermodynamic geothermobarometry and do not show systematic regional variation. A Raman carbonaceous material (CM) geothermometer has been recently calibrated for low-to medium-T metape-lites (150-650°C) (Beyssac et al, 2002;Rahl et al, 2005;Lahfid et al, 2010;Aoya et al, 2010;Kouketsu et al, 2014) and provides a powerful tool for studying the thermal structure of low-T metamorphic belts Bollinger et al, 2004;Negro et al, 2006Negro et al, , 2013Robert et al, 2010;Wiederkehr et al, 2011;Mathew et al, 2013;Yoshida et al, 2016). In this study, we determine the thermal structure of the Nishisonogi unit using Raman CM geothermometry.…”

Combined tracers in hot spring waters across the Kii Peninsula, Japan: Implications for the origins of metamorphic fluids of the SW Japan forearc

“…In this case, dehydrated water having the same isotopic composition as the mantle slab (8‰ and -35‰ of δ 18 O and δD, respectively) could be produced from marine clay, at temperatures of 36-260°C. The higher end of the metamorphic temperature did not conflict with a published estimate from a pelitic schist in the Sambagawa MZ (a mean value of 285°C; Yoshida et al, 2016). This meant that the δD-δ 18 O diagram could not be used to distinguish the origins of slab-derived fluid from clay dehydration.…”

Petrology and possible significance of barroisite–bearing metabasite from the Kebara Formation in NW Kii Peninsula

“…One possible scenario is that all constituents of the Kebara Formation once suffered EA facies metamorphism, and then most of them recrystallized under the lower temperature conditions of the PA or PBS facies. However, this scenario is rejected, because the irreversible nature of Raman spectra of CM geothermometry suggests that the matrix forming major lithotype, i.e., pelitic schist, of the Kebara Formation never experienced temperatures higher than~400°C (Yoshida et al, 2016).…”

“…The reported metamorphic conditions of the Kebara Formation belong to the PA or PBS facies (Kurimoto, 1986a;Tomiyoshi and Takasu, 2009;Yoshida et al, 2016), which means that the metamorphic temperature of the Kebara Formation is lower than 340°C (Fig. 4).…”

“…For this assemblage, P-T conditions of <340°C and 0.8 GPa are proposed based on thermodynamic calculations (Ueno, 1999(Ueno, , 2001. In pelitic rocks, geothermometry using the analysis of carbonaceous material (CM) by Raman spectroscopy yielded metamorphic temperatures of 302-340°C (Yoshida et al, 2016). Temperature estimates based on different methods all indicate that the Kebara Formation was metamorphosed at low temperature conditions.…”