Metamorphism and Zircon U-Pb Age of High-Pressure Mafic Granulites in Mian-Lüe Suture Zone, South Qinling Orogen
详细信息
- 责任者：Liang Sha (State Key Laboratory of Continental Dynamics ; Department of Geology ; Northwest University ; Xi’an 710069 ; China) ; Liu Liang
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(5)
- 关键词：麻粒岩 ; granulite ; 变质作用 ; metamorphism ; 铀—铅计时 ; U-Pb dating ; 秦岭 ; Qinling Mountains
- 页码：p.1657-1674
- 图表：illus., 5 tables, 63 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Mianxian-Lüeyang area is a representative of Mian-Lüe tectonic mélange belt. Two types of HP mafic granulites were recognized in Xujiaping region in the northern Mianxian County. According to petrographic study and P-T pseudosections calculated by THERMOCALC 3. 33,the peak metamorphic mineral assemblage of the first type granulite is associates with Grt 1 + Cpx + Pl 1 + Qz at the conditions of T = 800 ～ 860℃ ,P = 12. 4 ～ 14. 6kbar,and the retrograde assemblage is characterized by Grt 2 + Hbl + Pl 2 + Qz. The second type granulite is characterized by typical "white eye-socket"texture with albite or oligoclase,indicating that Omp was once existed in the rock. Therefore,the peak metamorphic mineral assemblage of the second granulite might be Grt 1 + Omp( ?) + Qz or Grt 1 + Cpx( ?) + Pl + Qz,and the condition is estimated to be T = 775 ～ 900℃ ,P > 19. 2kbar and T = 750 ～ 850℃ ,P = 16. 5 ～ 19. 8kbar, respectively. The rock was subsequently suffered two stages retrograded metamorphism,a granulite facies stage with mineral assemblage of Grt 2 + Opx + Hbl1 + Pl1 + Qz and an amphibolite facies stage with Grt3 + Hbl2 + Pl2 + Qz. The diversity initial composition might be the main factor that caused the different peak metamorphic mineral assemblages and conditions between the two types of the granulites. LA-ICP-MS zircon U-Pb dating obtained the metamorphic age of 214 ± 11Ma and the protolith age of 477Ma for the second type granulite,and the crystallization age of 215 ± 5Ma for the leucosome crossing the granulite,respectively. Combined with characteristics of trace elements,the age of 214 ± 11Ma might represents the amphibolite facies retrograded age. Thus a P-T-t path is established for these two types of HP mafic granulites,which reflects the process of subduction and collision of the Qinling orogen along the Mian-Lüe suture zone at Late Triassic.
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