西天山达巴特A型花岗岩的形成时代与构造背景  

Geochronological age and tectonic background of the Dabate A-type granite pluton in the west Tianshan.

作　　者：唐功建[1,2] 陈海红[3] 王强[1] 赵振华[1] Derek A．Wyman 姜子琦[1,2] 贾小辉[1,2] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学与地球化学重点实验室,广州510640 [2]中国科学院研究生院,北京100049 [3]中国地质大学(武汉)地质过程与矿产资源国家重点实验室,武汉430074 [4]悉尼大学地球科学学院地质与地球物理系,澳大利亚新南威尔士2006

出　　处：《岩石学报》2008年第5期947-958,共12页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2007CB411308);国家自然科学基金项目(40721063、40673037和40572042);中国科学院知识创新项目(KZCX2-YW-128)的资助

摘　　要：达巴特花岗斑岩侵入体位于西天山北部的赛里木湖北部，构造上属于准葛尔板块与伊犁-中天山板块之间的造山带。达巴特花岗岩斑岩具有A型花岗岩的特征，如高硅（SiO2=75．38％～77．61％）、碱（Na2O＋K2O=8．26％～10．10％）和Fe／（Fe＋Mg）（0．91～0．98），但低Al2O3（12．04～12．91％）和CaO（0．03％～0．42％），富集Rb、Th、U等大离子亲石元素和Nb、Ta、Zr、Hf等高场强元素，（Ga／Al）×10^4值变化于3．19～3．40之间，具有明显的负Eu、Ba和Sr异常，稀土配分显示“海鸥型”特征。这巴特花岗岩斑岩具有较高的Rb／Nh和Y／Nb比值，显示了A2型花岗岩的特征。LA—ICP—Ms锆石U—Pb测年结果显示达巴特岩体的侵位年龄为288．9±2．3Ma，并且一些锆石具有老的核（319．0±4．7），暗示花岗岩斑的源岩中可能包含有石炭纪的岩浆岩。结合区域地质和岩浆岩资料，我们认为西天山早二叠世处于伸展的背景中，可能与造山带后碰撞阶段的演化有关。The Dabate granitic porphyry pluton is located geographically to the north of the Sayram Lake, western Tianshan and, tectonieally, occurs in the orogenic belt between the Junggar plate to the north and the Yli-central Tianshan plate to the south. It mainly consists of biotite-bearing granite porphyries that are geochemically similar to A-type granites. They have high SiO2 （75.6% 77.6%）, alkalis （Na2O＋ K2O= 8.27% -8.70%）, Fe/（Fe＋Mg） （0.91-0.98） and （Ga/Al） ×10^4（3.19-3.40） values, but low Al2O3 （ 12.04% - 12.91% ） and CaO （0. 28% - 0. 34% ） contents. They are enriched in large ion lithophile elements （Rb, Th and U） and high field strength elements （Nb, Ta, Zr and Hf）, but have obvious negative Eu, Ba and Sr anomalies and ＂sea-gull＂-type rare earth element pattern. They also have relatively high Rb/Nb and Y/Nb ratios, indicating A2-type granite characteristics. Our new zircon LA-ICP-MS U-Pb age data suggest that the Dabate A-type granite porphyries were generated in the Early Permian （288.9 ±2. 3Ma）. Some residual zircon cores have a Late Carboniferous （319.0 ±4.7Ma） age, indicating that the source of the granitic porphyries likely contains Carboniferous magmatic rocks. Taking into account reginoal geological and magmatic rock data, we suggest that the northern Tianshan was in an extensional setting by the Early Permian, which was possibly related to post-collisional evolution of the orogenic belt.

关 键 词：LA-ICPMS锆石U-PB定年 A型花岗岩 后碰撞 西天山 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]