新疆谢米斯台中段火山岩岩石地球化学特征、锆石U-Pb年龄及其地质意义  

Igneous rocks geochemistry,zircon U-Pb age and its geological significance in the central section of Xiemisitai area,Xinjiang

作　　者：孟磊[1,2] 申萍[1] 沈远超[1] 刘铁兵[1] 宋国学[1] 代华五[1] 李成凯[2] 郎泽松 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院矿产资源研究重点实验室,北京100029 [2]有色金属矿产地质调查中心,北京100012

出　　处：《岩石学报》2010年第10期3047-3056,共10页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程重点项目(KZCX2-YW-107);国家自然科学基金项目(40972064);国家305项目(2006BAB07B01)资助

摘　　要：谢米斯台中段地区发育的火山岩主要为安山岩、英安岩和流纹岩。岩石地球化学研究表明,岩石的K2O、Na2O含量高(K2O=3.42%～9.85%;Na2O=0.48%～5.30%),大离子亲石元素(LILE)相对富集,高场强元素(HFSE)相对亏损,其中Nb、P、Ti强烈亏损,轻稀土元素(LREE)和重稀土元素(HREE)分馏较强;Pb同位素比值为206Pb/204Pb=18.435～19.409、207Pb/204Pb=15.535～15.602、208Pb/204Pb=38.36～39.213;火山岩具有高的初始εNd(t)值(+4.43～+6.65)和低的初始87Sr/86Sr值(0.700953～0.704435)。该地区流纹岩SIMS锆石U-Pb测年结果为422.5±1.9Ma。综合研究认为,谢米斯台中段地区火山岩是晚志留世准噶尔洋壳俯冲,在地幔楔形区,经过洋壳与富集地幔的局部熔融,经历了一定程度的分离结晶作用形成的中酸性岩浆喷发而成,在岩浆上升过程中有少量地壳物质的混染。The igneous rocks,occurred in the central section of the Xiemisitai area in Xinjiang,are made of the andesite,dacite and rhyolite. Geochemical data indicate that the igneous rocks have a high-K calc-alkaline composition (K2O=3.42%~9.85%; Na2O=0.48%~5.30%),and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) with a clear negative Nb,P and Ti anomaly. REE patterns show distinct enrichments in LREE relative to HREE. Lead isotope composition of the rocks span a narrow range (206Pb/204Pb=18.435~19.409,207Pb/204Pb=15.535~15.602,208Pb/204Pb=38.361~39.213). The rocks also exhibit high initial εNd(t) (+4.43^+6.65) ratios and low initial 87Sr/86Sr values (0.700953~0.704435). Volcanic activity occurred at 422.5±1.9Ma based on U-Pb (SIMS) analyses of zircons from the rhyolite. These data are consistent with a mature arc and suggest that the volcanic rocks were derived from the partial melting of multiple sources including oceanic crust and enriched mantle,with melts undergoing significant crystal fractionation and minor crustal assimilation during convergence between the paleo-Junggar ocean and the Xiemisitai mature arc in Late Silurian.

关 键 词：火山岩 地球化学 锆石U-PbSIMS测年 岛弧谢米斯台中段 

分 类 号：P588.14[天文地球—岩石学]