Diagenesis and metamorphism of Triassic flysch along profile Zoige-Lushan, northwest Sichuan, China

作者：Wang Hejing; Rahn M; Tao Xiaofeng; Zheng Nan; Xu Tingjing

来源：Acta Geologica Sinica (English Edition), 2008, 82(4): 917-U1.

• diagenesis
• metamorphism
• Songpan-Garze orogen
• Triassic flysch
• illite crystallinity
• Longmenshan fault

We used illite and chlorite crystallinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis (EMPA), b(0) geobarometer and chlorite geothermometer to quantify the diagenetic and metamorphic overprint on the Triassic flysch formations in the Songpan-Garze orogen along profile Zoige-Lushan, northwest Sichuan. Two anchizones, two epizones, one diagenetic zone and a transition belt in-between them are defined on the basis of the obtained data. Illite crystallinity correlates strongly with the best mean domain size of mica and moderately with chlorite crystallinity. 2M(1) white mica polytype are observed within the epizone whilst 2M(1) and 1M polytypes occur in the anchizone and diagenetic zone. Epizonal metamorphism reached maximum temperatures of 370 degrees C +/- 21 degrees C at low-to intermediate pressure conditions. Clay minerals underwent Ostwald ripening during metamorphism. Rocks from both sides of the Longmenshan fault reveal contrasting degrees of metamorphic overprint: on the northwest side of the Longmenshan fault, epimetamorphic conditions contrast with diagenetic rocks on the southeast side.

• 出版日期2008-8
• 单位成都理工大学; 北京大学