新疆阿尔泰克兰河中游泥盆纪花岗岩锆石LA-ICP-MS U-Pb年龄及地球化学特征  

LA-ICP-MS U-Pb Zircon Dating and Geochemistry of the Devonian Granites from the Middle Kelan River Valley of Altay in Xinjiang

作　　者：刘国仁[1,2] 董连慧[3] 高福平 陈剑祥 赵华[2] 王定胜 宋志勇 何立新[2] 秦纪华[2] 

机构地区：[1]中国地质大学,北京100083 [2]新疆维吾尔自治区地质矿产勘查开发局第四地质大队,新疆阿勒泰836500 [3]新疆维吾尔自治区地质矿产勘查开发局,新疆乌鲁木齐830000 [4]陕西省地矿局汉中地质大队,陕西汉中723000

出　　处：《地球学报》2010年第4期519-531,共13页Acta Geoscientica Sinica

基　　金：新疆维吾尔自治区1:5万区调专项资金项目(编号XJQDZ2006-01)资助

摘　　要：克兰河中游英云闪长岩和二长花岗岩的锆石LA-ICP-MS U-Pb年龄分别为400±2.3Ma（MSDW=1.1）和401±3.3 Ma（MSDW=1.2）, 表明岩体侵位于早泥盆世早期, 同时也暗示了岩体围岩康布铁堡组地层的形成时代早于401 Ma。所有花岗质岩石具有高的SiO2（67.80%~76.54%）和Al2O3（12.39%~16.07%）含量, 低P2O5 （0.02%~0.17%）和MgO＋FeO（2.22%~5.12%）含量, 富碱（K2O＋Na2O=5.58%~8.25%）, 具有低的CaO/Na2O （〈0.3）比值和高的A/CNK值（0.96~1.39）; 富集LREE和Th、U, 贫Ba、P、Sr、Ti、Nb, 呈现明显的Eu负异常（δEu=0.22~0.73）。以上特征表明该岩体属钙碱性准铝质-过铝质岩类, 具有岛弧花岗岩的典型特征。结合阿尔泰南缘的区域地质背景综合分析, 推测岩体形成于活动大陆边缘环境, 是在俯冲作用过程中由变泥质岩和变质杂砂岩脱水熔融的产物, 在部分熔融过程中有磷灰石、斜长石、钛铁矿等矿物的残留。LA-ICP-MS zircon U-Pb ages and whole rock geochemical data are reported in this paper for granitoid rocks in the Middle Kelan River valley on the southern margin of the Altay orogenic belt. Zircons with well-defined oscillatory zoning from tonalite and adamellite yielded mean 206Pb/238U ages of 400±2.3 Ma （MSDW=1.1） and 401±3.3 Ma （MSDW=1.2）, respectively, which indicate that the Kangbutiebao Formation was formed prior to 401Ma. The granitoid rocks have high SiO2 （67.8% to 76.8%）, total alkali （Na2O＋K2O） （5.58% to 8.25%） and Al2O3 （12.39% to 16.07%）, and low P2O5 （0.02% to 0.17%） and MgO＋FeO （2.22% to 5.12%）. In addition, they are characterized by high A/CNK values （0.96 to 1.34） and low CaO/Na2O（〈0.3）ratios, thus defined as calc-alkaline peraluminious granitoid rocks. They assume obvious negative anomalies of Ti, P, Sr, Ba and Eu （δEu=0.22~0.73） and obvious enrichment of LREE and Th, U, thus resembling granitoid rocks formed in an active continental margin. Combined with the tectonic evolution of the southern margin of Altay, the authors suggest that these granitoid rocks were generated by partial melting of the crust in an active continental margin, with the residues being plagioclase, ilmenite and apatite.

关 键 词：花岗岩 LA-ICP-MS 锆石U-PB年龄 地球化学 克兰河中游 阿尔泰 

分 类 号：P597[天文地球—地球化学] P588.12[天文地球—地质学]