JpGU-AGU Joint Meeting 2017

講演情報

[EJ] ポスター発表

セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP42] [EJ] 変形岩・変成岩とテクトニクス

2017年5月23日(火) 15:30 〜 17:00 ポスター会場 (国際展示場 7ホール)

コンビーナ:針金 由美子(産業技術総合研究所)、河上 哲生(京都大学大学院理学研究科)

[SMP42-P01] Prograde infiltration of Cl-rich fluid into the granulitic continental crust from a collision zone in Perlebandet, Sør Rondane Mountains, East Antarctica

*河上 哲生1東野 文子1,2Skrzypek Etienne1Satish-Kumar Madhusoodhan3Grantham Geoffrey4土屋 範芳2石川 正弘5坂田 周平1,6平田 岳史1,7 (1.京都大学、2.東北大学、3.新潟大学、4.ヨハネスブルグ大学、5.横浜国立大学、6.学習院大学、7.東京大学)

キーワード:流体、変成作用、部分溶融、塩素、大陸衝突

Timing of Cl-rich fluid infiltration is correlated with the pressure-temperature-time (P-T-t) path of upper amphibolite- to granulite-facies metamorphic rocks utilizing microstructures of Cl-bearing biotite in pelitic and felsic metamorphic rock from the continental collision zone (Perlebandet, Sør Rondane Mountains (SRM), East Antarctica). Microstructural observation indicates that the stable Al2SiO5 polymorph changed from sillimanite to kyanite + andalusite + sillimanite, and P-T estimates from geothermobarometry point to a counterclockwise P-T path characteristic of the SW terrane of the SRM (e.g., Osanai et al., 2013) In situ LA-ICPMS U-Pb dating of zircon inclusions in garnet yielded ca. 580 Ma, likely representing the age of garnet-forming metamorphism at Perlebandet.
Inclusion-host relationships among garnet, sillimanite, and Cl-rich biotite (Cl > 0.4 wt%) reveal that formation of Cl-rich biotite took place during prograde metamorphism in the sillimanite stability field. This process probably predated partial melting consuming biotite (Cl = 0.1-0.3 wt%). This was followed by retrograde, moderately Cl-bearing biotite (Cl = 0.1-0.3 wt%) replacing garnet. Similar timings of Cl-rich biotite formation in different samples, and similar f(H2O)/f(HCl) values of coexisting fluid estimated for each stage can be best explained by Cl-rich fluid infiltration during prograde metamorphism. Fluid-present partial melting at the onset of prograde metamorphism probably contributed to elevate Cl concentration (and possibly salinity) of the fluid, and consumption of the fluid resulted in the progress of dehydration melting. The retrograde fluid was released from crystallizing Cl-bearing partial melts or derived externally.
The prograde Cl-rich fluid infiltration in Perlebandet presumably took place at the uppermost part of the footwall of the collision boundary. Localized distribution of Cl-rich biotite and hornblende along large-scale shear zones and detachments in the SRM (Higashino et al., 2013; 2015) supports external input of Cl-rich fluids through tectonic boundaries during continental collision.