Ultra-high pressure metamorphism of granitic gneiss in the Yinggelisayi area, Altun Mountains, NW China  

作　　者：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 

出　　处：《Science China Earth Sciences》2004年第4期338-346,共9页中国科学（地球科学英文版）

基　　金：This work was supported jointly by the National Key Basic Research and Development Project of China (Grant No.G1999075508); the National Natural Science Foundation of China (Grant Nos. 40372088, 49972063, 140032010); Ministry of Education's Teacher Fund (Grant No. 40133020); the Opening Fund of Key Laboratory of Lithosphere tectonic, Deep Level Process and Exploration of Ministry of Education, China University of Geosciences, Wuhan.

摘　　要：A study on petrography and mineral chemistry of granitic gneiss from the Yinggeli-sayi 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/K2O ratio of 0.4—0.6, LREE-enriched patterns with (La/Yb)N ratio of 4.3—9.1 and large negative Eu anomaly (d Eu = 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 inter-beds 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 im-portant bearing for further discussion of the dynamic mechanism of the formation and exhuma-tion of the rocks in this region.

关 键 词：Altun Mountains  GRANITIC gneiss  supersilicic titanite  UHP metamorphism  continental deep subduction. 

分 类 号：P588.3[天文地球—岩石学]