10:15 〜 10:30
[T2-O-2] ヒマラヤ変成帯においてバロビアン分帯を構成する泥質岩石類の炭質物のラマン分光分析と地質温度について
キーワード：ラマン、炭質物、ヒマラヤ、カガン バレー、変成作用
Himalayan metamorphic belt resulted due to the India-Asia collision, Indian plate subduction, and exhumation back to the earth's surface. Previous studies (Rehman et al. 2007, JAES 29, 390-406), reported detailed thermobarometric structure of the Barrovian-type progressive metamorphic zonation (chlorite, biotite and garnet zones in the Lesser Himalayan Sequence:LHS), garnet-staurolite zones within the fault region, namely the Main Central Thrust (MCT), and garnet-staurolite to kyanite-sillimanite zones in the Higher Himalayan Crystalline (HHC) in the Himalayan metamoprhic belt, Kaghan Valley, Pakistan.
Conventional thermobarometery data yielded P–T estimates of 534 ± 17 °C and 7.6 ± 1.2 kbar for garnet zone, 526 ± 17 °C and 9.4 ± 1.2 kbar for staurolite zone, and 657 ± 54 °C at 10 ± 1.6 kbar for kyanite zone, respectively. P–T estimates from mafic rocks (amphibolites and eclogites) from HHC were 645 ± 54 °C at 10.3 ± 2.0 kbar and 746 ±- 59 °C at 15.5 ± 2.1 kbar.
In this study, we conducted Raman sectroscopic analyses on 21 thinsections mainly from pelitic and graphitic schists, and gneisses that contained graphite. Almost in all the studied samples, except a few, first order peaks of graphite (e.g. D1: ~1350 cm-1, G: ~1580 cm-1, D2: ~1620 cm-1, D3: ~1500 cm-1, and D4: 1245 cm-1) were observed. Peak-fitting on raw data of Raman spectroscopy was done and FWHM (Full Width at Half Maximum) were calculated for all the analyzed samples and temperature estimates were obtained using the RAMAN thermometry approach reporetd in Kouketsu et al., 2014, Island Arc, 23, 33-50; Aoya et al. 2010, J. Metamorphic Geol., 28, 895-914: and Kaneki & Kouketsu, 2022, Island Arc 2022;31:e12467). Raman data from graphite in samples of chlorite and biotite zones produced temeprature estimates from 350 ℃ to 440 ℃, of garnet and staurolite zone within the MCT zone from 460 ℃ to 540 ℃ (consistent with conventional thermobarometry), and of kyanite-sillimnite zones showed values of minimum T of 302 ℃ and maximum up to 664 ℃. The > 600 ℃ values are consistent with the previously reported data mentioned above, however the relatively lower T values in HHC samples may indicate surface damage possibly due to polishing. The slight jump in temperature values near the MCT zone (ca. 480 ℃ ~ 540 ℃) indicate shear-heat related thermal event due to the fault activation in that area.
Conventional thermobarometery data yielded P–T estimates of 534 ± 17 °C and 7.6 ± 1.2 kbar for garnet zone, 526 ± 17 °C and 9.4 ± 1.2 kbar for staurolite zone, and 657 ± 54 °C at 10 ± 1.6 kbar for kyanite zone, respectively. P–T estimates from mafic rocks (amphibolites and eclogites) from HHC were 645 ± 54 °C at 10.3 ± 2.0 kbar and 746 ±- 59 °C at 15.5 ± 2.1 kbar.
In this study, we conducted Raman sectroscopic analyses on 21 thinsections mainly from pelitic and graphitic schists, and gneisses that contained graphite. Almost in all the studied samples, except a few, first order peaks of graphite (e.g. D1: ~1350 cm-1, G: ~1580 cm-1, D2: ~1620 cm-1, D3: ~1500 cm-1, and D4: 1245 cm-1) were observed. Peak-fitting on raw data of Raman spectroscopy was done and FWHM (Full Width at Half Maximum) were calculated for all the analyzed samples and temperature estimates were obtained using the RAMAN thermometry approach reporetd in Kouketsu et al., 2014, Island Arc, 23, 33-50; Aoya et al. 2010, J. Metamorphic Geol., 28, 895-914: and Kaneki & Kouketsu, 2022, Island Arc 2022;31:e12467). Raman data from graphite in samples of chlorite and biotite zones produced temeprature estimates from 350 ℃ to 440 ℃, of garnet and staurolite zone within the MCT zone from 460 ℃ to 540 ℃ (consistent with conventional thermobarometry), and of kyanite-sillimnite zones showed values of minimum T of 302 ℃ and maximum up to 664 ℃. The > 600 ℃ values are consistent with the previously reported data mentioned above, however the relatively lower T values in HHC samples may indicate surface damage possibly due to polishing. The slight jump in temperature values near the MCT zone (ca. 480 ℃ ~ 540 ℃) indicate shear-heat related thermal event due to the fault activation in that area.