西天山巴音布鲁克地区早古生代成矿地质环境:岩浆岩及其时代和元素同位素约束  

Early Paleozoic geological environment of metallogeny in Bayinbuluk region,western Tien Shan: Igneous rocks and their dating,elementary and isotopic constraints

作　　者：邢浩[1] 赵晓波[1] 张招崇[1] 叶锦超[1] 冯博[1] 

机构地区：[1]地质过程与矿产资源国家重点实验室中国地质大学地球科学与资源学院,北京100083

出　　处：《岩石学报》2016年第6期1770-1794,共25页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(U1303292);国家科技支撑计划(2011BAB06B02);中国地质调查局工作项目(1212011085069)联合资助

摘　　要：西天山位于中亚造山带(CAOB)西南部,是其重要组成部分。CAOB晚古生代金属成矿环境和过程尤为典型,但早古生代成矿地质环境还不甚清楚。新疆巴音布鲁克地区出露(原定时代晚志留世)巴音布鲁克组火山岩夹浅海相碎屑岩和灰岩,是认识西天山早古生代成矿地质环境的难得对象。巴音布鲁克组出露于Nikolaev-那拉提山北缘断裂与Atbash-Inylchek-那拉提山南缘断裂之间的中天山,在巴音布鲁克地区典型发育,火山岩包括玄武岩、玄武安山岩、英安岩、流纹岩及相应的火山碎屑岩,其中侵入岩有正长斑岩和花岗闪长岩。LA-ICP-MS测得玄武安山岩、英安岩、正长斑岩、花岗闪长岩、流纹岩锆石U-Pb年龄分别为455.6±8.1Ma、444.5±1.9Ma、441.4±1.6Ma、455.4±5.3Ma、424±1.9Ma,岩浆活动于晚奥陶-早志留世,喷出和侵入时代接近,原定巴音布鲁克组地层时代晚志留世应改为晚奥陶-早志留世。这些岩浆岩具有相似的稀土元素地球化学特征,微量元素相比原始地幔均亏损Nb、Ta、P、Ti。玄武岩正的ε(t)=+1.6^+6.7,低的(^(87)~Sr/^(86)NdSr)i=0.70377~0.70489,指示岩浆源区具有亏损地幔特征,弱的Zr-Hf负异常,低的Th/Nb比值,较窄的同位素变化范围暗示地壳混染并不显著,微量元素及铅同位素特征(^(206)Pb/^(204)Pb=18.26~18.77,^(207)Pb/^(204)Pb=15.63~15.69,^(208)Pb/^(204)Pb=38.21~38.34)表明岩浆源区可能是俯冲流体及洋底沉积物交代的地幔楔橄榄岩部分熔融成因。西天山巴音布鲁克地区早古生代岩浆岩应是南天山洋晚奥陶-早志留世向北向中天山陆块之下俯冲在中天山-伊犁板块南缘活动大陆边缘的岩浆产物,指示了陆缘岩浆弧环境。这种陆缘弧环境有利于斑岩铜金成矿系统发育,值得高度关注相关铜金矿的地质找矿。The western Tien Shan is an important metallogenic belt that situated along the southwest margin of the Central Asian Orogenic Belt（ CAOB）.The geological environment and metallogeny of the CAOB during Late Paleozoic are well concerned,however,the geodynamic setting of the CAOB during Early Paleozoic remains unclear and the metallogenic potential of this period is also poorly documented.Volcanic rocks and interlayered neritic clastic and limestone of the Upper Silurian Bayinbuluke Formation offer a rare opportunity for understanding these issues.The Bayinbuluke Formation is typically exposed in the Bayinbuluke area of the Xinjiang Central Tien Shan,which is generally sandwiched between the Nikolaev-North Nalati Fault and the Atbash-Inylchek-South Nalati Fault.The rocks in the Bayinbuluke area comprise of basalt,basaltic andesite,dacite,rhyolite and volcanic clastics that intruded by syenite porphyry and granodiorite.Zircon LA-ICP-MS U-Pb dating of the basaltic andesite,dacite,syenite porphyry,granodiorite,rhyolite yield ages of 455.6 ± 8.1Ma,444.5 ± 1.9Ma,441.4 ± 1.6Ma,455.4 ± 5.3Ma and 424 ± 1.9Ma,respectively,confirming that the magmatism in this area occurred during Late Ordovician to Early Silurian rather than Late Silurian as previously suggested.The element and isotopic geochemical characteristics of volcanic and intrusive rock show clear similarities,e.g.,all the igneous rocks have the same chondrite-normalized rare earth element patterns and prominent negative Nb-Ta and P-Ti anomalies on mantle-normalized trace element diagrams.Basalts have positive εNd（ t） values（ ＋ 1.6 - ＋ 6.7）,and low（-（87）Sr /-（86）Sr）iratios（ 0.70377 - 0.70489）.Sr-Nd isotopic compositions of these rocks indicated that the primitive magma was possibly originated from a depleted mantle source.The rocks all have low Th / Nb ratios,narrow isotopic variations,and slightly negative Zr-Hf anomalies,suggesting insignificant crustal contamination.They are enriched in large ion lithophile elements（ LILE）

关 键 词：岩浆岩 锆石U-PB测年 元素和同位素 早古生代 巴音布鲁克组 西天山 

分 类 号：P588.12[天文地球—岩石学] P588.14[天文地球—地质学]