新疆贝勒库都克铝质A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学及其成因

LA-ICP-MS Zircon U-Pb Age,Geochemistry and Genesis of the Aluminous A-type Granite in Beilekuduke,Xinjiang

新疆东准噶尔卡拉麦里地区是一个重要的锡成矿带,分布有多种类型花岗岩。贝勒库都克岩体位于锡成矿带中部,由黑云母正长花岗岩和黑云母二长花岗岩组成。本文通过精确的LA-ICP-MS锆石U-Pb测年获得贝勒库都克含锡黑云母正长花岗岩年龄为283±2Ma,MSWD=0.14(95%置信度),时代属于早二叠世,这与东准噶尔后碰撞深成岩浆活动的范围(330～265Ma)相吻合。岩石地球化学研究表明,贝勒库都克岩体富硅(SiO2=75.25%～76.67%),低铝(Al2O3=11.91%～12.86%),贫镁(MgO=0.02%～0.18%)和钙(CaO=0.39%～0.89%),富碱(Na2O+K2O=8.08%～8.97%),K2O>Na2O,NK/A=0.86～0.95(平均0.92),A/NCK=0.97～1.02,富集Rb、K等大离子亲石元素及Zr、Hf等高场强元素,Ba、Nb、Sr强烈亏损,δEu=0.01～0.11,其FeOt/MgO(12.71～84.51,平均34.55)和10000Ga/A1(2.97～4.20)值大,HFSE元素(Zr+Nb+Ce+Y=191.8×10-6～353.3×10-6)含量高,明显不同于典型的I型和S型花岗岩,基本属于典型的铝质A型花岗岩。年代学和地球化学综合研究表明,贝勒库都克铝质A型花岗岩是壳幔混合成因,是准噶尔地区后碰撞幔源岩浆底侵作用导致大陆地壳垂向生长过程的记录者。

Several types of granites are distributed in the Kalamaili area of East Junggar,Xinjiang,which constitutes an important tin metallogenic belt.The Belekuduke granite intrusion is situated in the centre of the tin metallogenic zone consisting of biotite syenite granite and biotite monzogranite.High-precision LA-ICP-MS zircon U-Pb dating reveals that the ore-hosting biotite syenite granite in the Belekuduke granite intrusion formed at 283±2Ma,which belongs to the Early Permian and coincides with the age（330～265 Ma）of post-collisional magma activity around the eastern Junggar area.Petrological and geochemical study show that the intrusion is characterized by high silicon（SiO2=75.25%～76.67%）,low aluminum（Al2O3 =11.91%～12.86%）,depleted magnesium and calcium （MgO=0.02%～0.18%,CaO=0.39%～ 0.89%）and abundant alkali（Na2O＋K2O=8.08%～8.97%,K2ONa2O,NK/A=0.86～0.95（the average is 0.92）,A/NCK=0.97～1.02）.Enrichment of LILE（such as Rb and K）and HFSE（such as Zr and Hf）,depletion of Ba,Nb and Sr,with the lowestδEu（δEu=0.01～0.11）,the value of the FeOt/ MgO（12.71～84.51,the averaging 34.55）and high 10000Ga/Al（2.97～4.20）and HFSE（Zr＋Nb＋Ce ＋Y=191.8×10-6～353.3×10-6）,indicate that it is different from I-and S-type granites,suggesting that biotite granites are actually typical aluminous A-type granite.Geochronology and geochemisty shows that the Belekuduke aluminous A-type granite resulting from mixing of crust and mantle is the recorder of vertical growth of continental crust triggered by underplaing of post-collisional mantle-driven magma in East Junggar.