14:15 〜 14:30
[SMP27-09] Pressure-temperature estimate of a pelitic schist from the Sanbagawa belt (Mt. Funaokayama, Kii Peninsula, SW Japan)
キーワード：エクロジャイト相、沈み込み帯、海嶺の沈み込み
The Sanbagawa belt in SW Japan is a high-pressure intermediate type metamorphic belt which extends about 800 km from east to west. The Sanbagawa belt records three metamorphic stages: early metamorphism, eclogite-facies metamorphism and main metamorphism (Endo et al., 2012). Based on the studies of eclogite units in the Besshi and Kotsu regions, the eclogite-facies and main metamorphisms are considered to have occurred under high-temperature condition owing to the approach of spreading ridge (Aoya et al., 2003). In order to reveal the lateral variations in the timing of ridge approach and metamorphism across the entire Sanbagawa belt, studies from other areas than Shikoku Island are needed. Endo et al. (2013) reported a pressure-temperature (P-T) path of garnet-amphibolite from Mt. Funaokayama, and concluded that it experienced prograde P-T path higher-temperature than eclogites from the Kotsu region in Shikoku. However, whether the pelitic schists from Mt. Funaokayama experienced similar P-T evolution with the garnet-amphibolite or not has not been investigated.
In this study, we report P-T condition of a pelitic schist at its pressure peak from Mt. Funaokayama. Based on detailed petrographic observation, we recognized five metamorphic stages: garnet-core growth stage (Stage 1), garnet-mantle growth stage (Stage 2), garnet-rim and plagioclase-core growth stage (Stage 3), plagioclase-rim growth and matrix stage (Stage 4) and retrograde stage (Stage 5). We consider that Stage 2 mineral assemblage represented by mineral inclusions in the garnet mantle records the highest pressure condition. Using Zr-in-rutile geothermometer (Tomkins et al., 2007) and garnet + rutile + quartz + water + titanite + clinozoisite equilibria (e.g., Endo et al., 2013), the peak-pressure P-T condition at Stage 2 was estimated as ~560oC, ~13 kbar. This result suggests that the pelitic schist of Mt. Funaokayama also experienced eclogite-facies metamorphism together with the garnet-amphibolite. The peak-pressure P-T condition from Mt. Funaokayama is higher-temperature than the eclogites in Shikoku (Aoya et al., 2009) possibly due to closer approach of a ridge, mostly supporting the conclusion of Endo et al. (2013).
References
Aoya et al. (2003) Geology, 31, 1045-1048.
Aoya et al. (2009) Terra Nova, 21, 67-73.
Endo et al. (2012) Lithos, 146-147, 183-201.
Endo et al. (2013) Journal of Mineralogical and Petrological Sciences, 108, 189-200.
Tomkins et al. (2007) Journal of Metamorphic Geology, 25, 703-713.
In this study, we report P-T condition of a pelitic schist at its pressure peak from Mt. Funaokayama. Based on detailed petrographic observation, we recognized five metamorphic stages: garnet-core growth stage (Stage 1), garnet-mantle growth stage (Stage 2), garnet-rim and plagioclase-core growth stage (Stage 3), plagioclase-rim growth and matrix stage (Stage 4) and retrograde stage (Stage 5). We consider that Stage 2 mineral assemblage represented by mineral inclusions in the garnet mantle records the highest pressure condition. Using Zr-in-rutile geothermometer (Tomkins et al., 2007) and garnet + rutile + quartz + water + titanite + clinozoisite equilibria (e.g., Endo et al., 2013), the peak-pressure P-T condition at Stage 2 was estimated as ~560oC, ~13 kbar. This result suggests that the pelitic schist of Mt. Funaokayama also experienced eclogite-facies metamorphism together with the garnet-amphibolite. The peak-pressure P-T condition from Mt. Funaokayama is higher-temperature than the eclogites in Shikoku (Aoya et al., 2009) possibly due to closer approach of a ridge, mostly supporting the conclusion of Endo et al. (2013).
References
Aoya et al. (2003) Geology, 31, 1045-1048.
Aoya et al. (2009) Terra Nova, 21, 67-73.
Endo et al. (2012) Lithos, 146-147, 183-201.
Endo et al. (2013) Journal of Mineralogical and Petrological Sciences, 108, 189-200.
Tomkins et al. (2007) Journal of Metamorphic Geology, 25, 703-713.