Geochemical Characteristics and Metamorphic P-T Paths of the Bulunkuole Group in Taxkorgan, Western Kunlun
详细信息
- 责任者：Liu Wenping (State Key Lab. of Isotope Geochemistry ; Chinese Academy of Sciences ; Guangzhou 510640 ; China) ; Wang He
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(3)
- 关键词：角闪片麻岩 ; hornblende gneiss ; 岩石地球化学 ; lithogeochemistry ; P—T—t轨迹 ; P-T-t trace ; 昆仑山 ; Kunlun Mountains
- 页码：p.923-937
- 图表：illus., 4 tables, 44 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Bulunkuole Group is an important metamorphic terrain exposed in the Western Kunlun Orogen but is debatable about its genesis.It is mainly composed of Grt-Pl-Hbl gneiss and khondalite at Maryang in Taxkorgan,western Kunlun.According to the geochemical characteristics,the Grt-Pl-Hbl gneiss may be subdivided into two types:the first type has higher content of total REE(∑REE=190.2×10-6～359.1×10-6) than that of the other type of Grt-Pl-Hbl gneiss(∑REE=89.28×10-6～113.1×10-6),and gets poorer from LREE to HREE((La/Yb)N=4.28～5.79),with the feature of E-MORB;the second is poor in LREE((La/Yb)N=0.59～0.84) and horizontal HREE pattern((Gd/Yb)N=0.99～1.07) with the feature of N-MORB.However,both kinds of the Grt-Pl-Hbl gneiss exhibit positive Ba but negative Sm,Cr,Zr,Hf and Ti anomalies with slightly negative Nb and Ta anomalies,showing the feature of the island arc tholeiite.Discrimination diagrams indicate that the protoliths of the khondalites are shale and greywacke formed in an island arc.Thus,the protoliths of the Grt-Pl-Hbl gneisses and the khondalites were likely developed in the island arc setting.Further petrography and mineral chemical data,combined with P-T estimates,indicate three metamorphic stages in the Grt-Pl-Hbl gneiss:M1 is a high-pressure metamorphic stage,with a mineral assemblage of Grt+Hbl1+Pl1+Qtz and the P-T conditions of around 850～870℃ with 12.9～13.3kb;the retrograde stages M2 and M3 have mineral assemblages of Hbl2+Pl2+Qtz and Hbl3+Pl3+Kfs+Bt+Qtz respectively,and the P-T estimates are respectively 730～770℃/7.3～7.8kb and 680～740℃/4.7～5.7kb.Whereas the khondalite is considered to have undergone three metamorphic stages:the P-T condition of the early M1 stage is implied to be same with that of peak assemblage in the Grt-Pl-Hbl gneiss(850～870℃/12.9～13.3kb);its peak M2 stage and post-peak M3 assemblages are respectively Grt2+Pl2+Bt2+Sil+Qtz and Grt3+Pl3+Bt3+Sil+Mus+Qtz,with the corresponding P-T estimates of 800～830℃/7.9～9.2kb and 670～700℃/5.1～5.6kb.The three metamorphic stages of the khondalite are interpreted to match with the M1,M2 and M3 of the Grt-Pl-Hbl gneiss.The calculated results suggest clockwise P-T paths with a peak high-pressure stage overprinted by an upper amphibolite-or mid-pressure granulite facies metamorphism followed by a lower amphibolite facies metamorphism,which are interpreted to form in the Hercynian collision-related tectonic setting.They are possibly associated with the closure of Paleo-Tethyan Ocean,followed by the intracontinental shearing during the Indosinian tectonic uplift.