西准噶尔库什库都克石英闪长岩地球化学、年代学及地质意义

库什库都克石英闪长岩位于新疆西准噶尔的达尔布特晚古生代中酸性岩浆岩带中。通过LA-ICP-MS锆石U-Pb定年，结合锆石阴极发光图像和U、Th元素特征，获得石英闪长岩的年龄为305.3±2.8 Ma（n=19，MSWD=0.17），时代属晚石炭世晚期（C2）。石英闪长岩呈半自形不等粒结构，块状构造，矿物成分主要为斜长石、石英、角闪石和黑云母等，局部发育含柱状辉石的石英辉长闪长岩。岩石的SiO2含量为59.38%~63.37%，全碱变化于6.55%~7.51%；里特曼指数( σ )变化于2.62~2.88，铝饱和指数(A/CNK值)介于0.83~0.90，为准铝质；岩石轻稀土富集且轻重稀土元素分馏明显，（La/Yb）N 为2.99~3.66，负Eu异常（δEu为0.64~0.79）；岩石相对富集Ba、Nd、Zr、K和LREE等元素，而相对亏损Rb、Nb、Th、Sr、P、Ti和HREE等元素，属高钾钙碱性准铝质I型花岗岩类岩石。石英闪长岩地球化学特征表明其为上地壳变质玄武岩熔融的产物，在岩浆演化过程中发生了以斜长石、辉石、金红石和磷灰石为主的分离结晶作用，而角闪石基本未发生分离结晶。区域构造环境演化分析认为西准噶尔不仅在晚石炭世早期存在与俯冲作用相关的岛弧花岗岩，在晚石炭世晚期-早二叠世早期也存在持续俯冲作用，在此环境下形成了与俯冲作用相关的岛弧型库什库都克石英闪长岩。

LA-ICP-MS Zircon U-Pb Geochronology and Geochemistry of the Kushenkuduke Quartz Diorite in Western Junggar and Its Tectonic Significance

The Kushenkuduke quartz diorite is located in the Late Paleozoic intermediate-acidic magmatic rocks belt along Dalbutearea in Western Junggar, Xinjiang. LA-ICP-MS zircon U-Pb dating yields an age of 305.3±2.8 Ma （n=19, MSWD= 0.17） for thequartz diorite, indicating that it was generated during late stage of the Late Carboniferous (C2). The quartz diorite has a hypidiomorphicheterogranular texture and a massive structure, and consists mainly of plagioclase, quartz, amphibole, and biotite, etc. A small amountof quartz gabbro diorite with columnar pyroxene has also been observed in this pluton. The geochemical analyses show that the plutonis characterized by SiO2 of 59.38%~63.37%, total alkali (Na2O+K2O) of 6.55%~7.51%, and Rittman index σ of 2.62~2.88, aluminumHREE=3.86~4.38, (La/Yb)N=2.99~3.66 ), with negative Eu anomalies (δEu=0.64~0.79) . The trace elements are characterized by Ba,Nd, Zr, K, LREE enrichment, and Rb, Nb, Th, Sr, P, Ti, HREE depletion. All the features suggest a high K calcic-alkaline I-typegranite. The quartz diorite was likely derived from metabasalt in the upper crust, and subsequently underwent the fractionalcrystallization of plagioclase, pyroxene, rutile, and apatite without amphibole. Based on comprehensive analysis of the genetic type ofthe quartz diorite and evolution of regional tectonic environment, we suggest that when the Junggar Ocean perpetually continued itsdeep subduction toward north from the early Late Carboniferous to the Early Permian, and the Kushenkuduke quartz diorite of theisland-arc type was formed during this tectonic evolution.