新疆库米什地区晚石炭世-早二叠世花岗岩年代学、地球化学及其地质意义

南天山东缘库米什地区花岗岩广泛出露，沿库米什断裂形成NWW向花岗岩带.该地区发现有忠宝和桑树园子矽卡岩型白钨矿床，矿化与二云母花岗岩关系密切.锆石U-Pb LA-ICP-MS定年分别获得忠宝岩体年龄为296±4 Ma，桑树园子岩体年龄为293±3 Ma，形成时代为晚石炭世-早二叠世.两岩体总体具有高SiO₂(72.51%~74.84%，70.68%~74.14%)，K₂O＞Na₂O，铝饱和(A/CNK=1.11~1.48，1.05~1.11)，可见原生白云母矿物等特征，反映了同碰撞S型花岗岩的特点.样品总体富集LILE元素、亏损HFSE元素，稀土元素表现为轻稀土富集、重稀土亏损的“右倾”型特征，具中等的负Eu异常.综合岩体的I_Sr值(0.707 6~0.708 8和0.706 5~0.707 7)、负的ε_Nd(t)值(-6.3~-7.1和-4.7~-5.1)、岩体单阶段模式年龄(T_DM)值(1.59~1.8 Ga和1.50~1.56 Ga)及古老的继承锆石年龄(2.5~0.8 Ga)分析认为，忠宝及桑树园子岩体为库米什地区星星峡群变泥质岩云母类矿物脱水部分熔融的产物，并可能混有杂砂岩成分，而南天山东部存在古老基底.本次研究显示南天山洋东部(库米什地区)于晚石炭世-早二叠世最终闭合，早中二叠世A型花岗岩及基性岩浆活动的出现表明该地区进入板内伸展阶段.富钨的星星峡群是本地区钨矿化可能的矿源层，早二叠世挤压向伸展的转换阶段为南天山东部钨矿有利的成矿构造体制，经历多旋回构造重熔的星星峡群在早二叠世造山过程的再次“重熔”作用致使成矿元素最终富集成矿. 

Geochronology, Geochemistry and Geological Significance of Late Carboniferous-Early Permian Granites in Kumishi Area, Xinjiang

Granitoids are widely distributed in east part of south Tianshan orogen, forming a NWW orientated granite belt along Kumishi fault. Zhongbao and Sangshuyuanzi skarn-type tungsten deposits have been discovered in this region and the mineralization is closely related to two-mica granites. LA-ICP-MS U-Pb zircon dating yields the ages of Zhongbao and Sangshuyuanzi granites of 296±4 Ma and 293±3 Ma, respectively, which belong to Late Carboniferous-Early Permian. Both of the granites are peraluminous (A/CNK=1.11-1.48, 1.05-1.11) with high contents of SiO₂ (72.51%-74.84%, 70.68%-74.14%) and primary muscovites, which show the characteristics of syn-collision S-type granites. The samples are characterized with enriched LILE, LREE and loss of HFSE, with HREE showing moderate negative Eu anomalies. I_Sr values of two granites range from 0.707 6 to 0.708 8 and 0.706 5 to 0.707 7; ε_Nd(t) values range from -6.3 to-7.1 and -4.7 to -5.1; Nd single-stage modle ages (T_DM) range from 1.59 to 1.8 Ga and 1.50 to 1.56 Ga, and the old inherited zircon ages range from 2.5 to 0.8 Ga. The above data indicate that the two granites are derived from partial melting of metapelites of Xingxingxia group and might contain mix greywacke ingredients, suggesting that there exists Precambrian basement in the eastern part of South Tianshan. Based on this research and previous studies as well, we are convinced that South Tianshan ocean finally closed in Late Carboniferous-Early Permian and the appearance of A-type granites and mafic magmatism means that the south Tianshan orogenic belt enters the post-orogenic stage.Tungsten-rich Xingxingxia Group is the possible source of regional tungsten mineralization and the conversion stage from syn-collision to post-collision is the advantageous matallotecttonic system. Xingxingxia Group that had experienced the polycycle tectonism remelted again in orogenic processes in Early Permian, resulting in the final concentration of ore-forming elements.