Metamorphism, Zircon U-Pb Dating and Tectonic Implications of Garnet Amphibolites from Hongliuxia, Dunhuang, Gansu Province
详细信息
- 责任者：Wang Zhongmei (Institute of Geology and Geophysics ; Chinese Academy of Sciences ; Beijing 100029 ; China) ; Xiao Wenjiao
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(5)
- 关键词：石榴子石岩 ; garnetite ; 角闪岩 ; amphibolites ; 铀—铅计时 ; U-Pb dating ; 甘肃 ; Gansu Province
- 页码：p.1685-1697
- 图表：illus., 5 tables, 54 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The protolith of the Hongliuxia amphibolites is tholeiite formed in immature arc,and the typical mineral assemblages are garnet ( Grt) ,amphibole ( Amp) ,diopside ( Di) and plagioclase ( Pl) . The coarse-grain garnet porphyroblasts usually display obvious zonings. Petrographic and mineral chemistry indicate that the amphibolites have undergone four successive stages: prograde,peak, isothermal decompression and isobaric cooling. The prograde metamorphic assemblages ( M1) are the minerals preserved in garnet porphyroblasts ( GrtⅠ + AmpⅠ + PlⅠ + Qtz) ,and the P-T metamorphic conditions are estimated to be 550℃ to 600℃ and 0. 3 Gpa to 0. 5Gpa; the peak metamorphic assemblages ( M2) are the mantle part of garnet and the minerals in the matrix ( GrtⅡ + AmpⅡ + Di + PlⅡ + Qtz) ,P-T estimates give peak metamorphic conditions of 650℃ to 780℃ and 0. 8 Gpa to 0. 9Gpa; the M3 stage is characterized by the Pl Ⅲ + Amp Ⅲ corona around garnet porphyroblasts,which infer an obvious decompression process,and the temperature of metamorphism is estimated to be 630℃ to 700℃ ; the temperature of the M4 stage drop a lot,which is inferred from the breakdown of diopside to produce AmpⅣ + PlⅣ. The estimated P-T conditions indicate a clockwise P-T-t path. The tectonic evolution history is: plate subduction cause high-temperature metamorphism,after that the crust tends to be thin,then the deep rock cool down to the normal geothermal gradient. The crystallization age of garnet-bearing amphibolite is 1611 ± 6Ma,which is contemporary to the breakup Columbia Supercontinent,so the Tarim Craton may connect with the breakup of Columbia Supercontinent.
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