新疆东天山玉海西岩体地球化学特征及其地质意义
Geochemical Features and Geological Significance of Yuhaixi Plutons in Eastern Tianshan, Xinjiang

玉海西Mo矿位于东天山大南湖-头苏泉岛弧带东段，为新疆有色地勘局704队在2015年新发现的钼矿床.矿区出露的岩石主要为石炭系盐池组、新近系葡萄沟组砂砾岩及一套片麻状花岗岩-闪长岩-辉长岩脉复式岩体.LA-ICP-MS锆石U-Pb定年结果显示，玉海西片麻状花岗岩、闪长岩分别侵位于364Ma和306Ma.玉海西岩体均具有正的εHf(t)(10.5～14.2)和εNd(t)(0.9～4.0)值，较低的 I-Sr (0.703 282～0.704 111)含量，显示新生地壳或亏损地幔来源特征.其中，片麻状花岗岩具有较小的Mg#值(22～27)、Zr/Hf(28～33)、Ti/Zr(10～29)和Ti/Y(94～149)比值，表明其来源于新生下地壳.闪长岩和辉长岩具有较低的SiO2(47.55%～57.54%)含量，较高的Mg#值(51～59)及Ti/Zr(20～380)、Ti/Zr(246～269)比值，表明其来源于亏损地幔；此外，样品富集LREEs和LILEs(Rb、Sr等)，Ce/Pb(6.5～12.0)比值较低，表明有壳源物质的加入.结合区域地质研究成果，表明玉海西片麻状花岗岩来源于新生下地壳的部分熔融，由古亚洲洋向北俯冲引起；闪长岩同样形成于古亚洲洋俯冲阶段，由亏损地幔并混染地壳形成；辉长岩脉来源于亏损地幔的部分熔融并混染地壳成分，形成于碰撞后伸展阶段，晚于闪长岩(306 Ma)侵位.
The Yuhaixi Mo deposit, located in the eastern part of the DananhuTousuquan island arc belt, was discovered by the No.704 Geological Party of Xinjiang Geological Exploration Bureau for Nonferrous Metals in 2015. Rocks occurring at Yuhaixi contain the Carboniferous Yanchi Formation, Neogene Putaogou Formation and felsicmafic plutons (gneissic granite, granite, diorite and gabbro dike). LAICPMS zircon UPb dating reveals that gneissic granite and diorite replaced at ca. 364Ma and 306Ma, respectively. Yuhaixi intrusions are characterized by highεHf(t)(10.5-14.2) andεNd(t)(0.9-4.0) values, and low I-Sr (0.703282-0.704111) values, indicating depletedmantle or juvenilecrust sources. The gneissic granite is characterized by low Mg# value (22-27), and Zr/Hf (28-33), Ti/Zr (10-29) and Ti/Y (94-149) ratios, implying a juvenilecrust source. The diorite and the gabbro dike are marked by low Si2O content (47.55%-57.54%), high Mg# values (51-59), and Ti/Zr (20-380) and Ti/Zr (246-269) ratios, which indicate that these rocks were likely formed by the part melting of the depleted mantle. However, diorite and the gabbro dike samples are rich in LREEs and LILEs (e.g., Rb, Sr), with low Ce/Pb ratios (6.5-12.0), suggesting the mixing of crustal component. Combining with the regional geological studies, the Yuhaixi gneissic granite was likely derived from the juvenile low crust, related with the north subduction of the Kangguer ocean plate; the diorite was also formed under a subducion setting by the partial melting of depleted mantle, and mixed with crustal component when it traversed the crust; the gabbro dike was probably derived from the depleted mantle, mixing with crustal component as well, in a postcollisional extension setting, the age of which was latter than 306Ma