| Ultra-high pressure metamorphism of granitic gneiss in the Yinggelisayi area, Altun Mountains, NW China |
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| 作者姓名： | LIU Liang SUN Yong LUO Jinhai WANG Yan CHEN Danling & ZHANG Anda The Key Laboratory of Continental Dynamics Ministry of Education |
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| 作者单位： | LIU Liang，SUN Yong，LUO Jinhai，WANG Yan，CHEN Danling & ZHANG Anda The Key Laboratory of Continental Dynamics，Ministry of Education，Department of Geology，Northwest University，Xi抋n 710069，China |
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| 基金项目： | 国家重点基础研究发展计划(973计划)，国家自然科学基金，Ministry of Education's Teacher Fund，the Opening Fund of Key Laboratory of Lithosphere tectonic |
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| 摘 要： | With the discovery and further studies of high- pressure (HP) to ultra-high-pressure (UHP) eclogites and UHP garnet lherzolite in the Altun Mountains1 9], it becomes interesting if the country rocks of these HP-UHP metamorphic rocks also underwent HP-UHP metamorphism, which will be crucial for understand-ing the relationship of HP-UHP metamorphic rocks and their country rocks, the mechanism of their forma-tion and uplifting and the existence of continental deep subduction in the are…
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Ultra-high pressure metamorphism of granitic gneiss in the Yinggelisayi area, Altun Mountains, NW China |
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| LIU Liang,SUN Yong,LUO Jinhai,WANG Yan,CHEN Danling,ZHANG Anda.Ultra-high pressure metamorphism of granitic gneiss in the Yinggelisayi area, Altun Mountains, NW China[J].Science in China(Earth Sciences),2004,47(4). |
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| Authors: | LIU Liang SUN Yong LUO Jinhai WANG Yan CHEN Danling ZHANG Anda |
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| Abstract: | A study on petrography and mineral chemistry of granitic gneiss from the Yinggelisayi area in the Altun Mountains of the northwestern China demonstrates that the granitic gneiss experienced a complicated multi-stage metamorphism. The peak-stage mineral assemblage is garnet+perthite(before exsolution)+titanite(before exsolution)+kyanite+zoisite +quartz/ coesite ±clinopyroxene with minor apatite and rutile. The exsolution of rod-like plagioclase +amphibole is contained within the core part of coarse-grained titanite, and the Si value per unit formula of the titanite is estimated to be 1.032-1.047, which implies that the titanite contains Si with six-fold coordination and the precursor titanite is hence of supersilicic titanite and suggests that the CaSi2O5 component in the titanite is 3.1%-4.7%. The P-T condition of peak metamorphism is estimated to be 3.7-4.3GPa at 1000℃. High-Al titanite inclusions are also found in the garnet.All of these suggest that the granitic gneiss underwent UHP metamorphism. The granitic gneiss has SiO2 content (＞70%), Al2O3 (12.58%-14.08%), high K2O content (＞5%) with Na2O/K2Oratio of 0.4-0.6, LREE-enriched patterns with (La/Yb)N ratio of 4.3-9.1 and large negative Eu anomaly (δEu = 0.06-0.59), which indicate that the protolith of the granitic gneiss is the product of anatexis of the middle or upper crustal rock. The UHP granitic gneiss, together with the interbeds of UHP metamorphic garnet lherzolite and garnet-bearing intermediate-basic gneiss in the outcrops, suggests that they all might undergo continental deep subduction, which will have important bearing for further discussion of the dynamic mechanism of the formation and exhumation of the rocks in this region. |
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| Keywords: | Altun Mountains granitic gneiss supersilicic titanite UHP metamorphism continental deep subduction |
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