新疆西准噶尔接特布调A型花岗岩年代学、地球化学及岩石成因  

Geochronology, Geochemistry and Petrogenesis of the Jietebutiao A-type Granites in West Junggar, Xinjiang

作　　者：杨高学[1,2] 李永军[1,2] 张兵[3] 汪雅兵[1,2] 刘振伟[1,2] 严镜[1,2] 田陟贤[1,2] 

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [3]新疆维吾尔自治区地质矿产勘查开发局第七地质大队,新疆乌苏833000

出　　处：《地球学报》2013年第3期295-306,共12页Acta Geoscientica Sinica

基　　金：中央高校基本科研业务费专项资金(编号:CHD2010ZY005);新疆维吾尔自治区地质矿产勘查开发局国土资源大调查项目(编号:XJZBKD2008-04;XJQDZ2009-03)联合资助

摘　　要：西准噶尔乃至整个北疆地区广泛发育晚古生代后碰撞花岗岩类。接特布调岩体作为一个典型的代表,岩石类型主要有中粗粒二长花岗岩和正长花岗岩,是认识西准噶尔花岗岩岩石成因及构造-岩浆演化的关键。本文对接特布调岩体进行高精度锆石LA-ICP-MSU-Pb测年,获得二长花岗岩和正长花岗岩的加权平均206Pb/238U年龄分别为(287±9)Ma(n=10,MSWD=0.92)和(278±3)Ma(n=14,MSWD=0.43),确定其形成于早二叠世,属于300Ma前后准噶尔周边地区后碰撞岩浆活动的产物。岩石地球化学研究表明,前人认为的接特布调I型花岗岩应归属于A型花岗岩。正长花岗岩具有高硅(SiO2:76.11%～76.82%),富碱(Na2O+K2O:8.47%～8.49%),低钛(TiO2:0.04%～0.05%),贫钙(CaO:0.36%～0.42%)的特征。二长花岗岩与其类似,高硅(SiO2:68.35%～71.80%),富碱(Na2O+K2O:6.80%～7.86%),低钛和钙(TiO2:0.29%～0.82%,CaO:1.76%～2.87%),均属于准铝质或弱过铝质(ACNK:0.98～1.09)高钾钙碱性系列。正长花岗岩相对于二长花岗岩具有相对较低的稀土元素总量(ΣREE)(分别为23.8×10-6～49.3×10-6,95.23×10-6～222.2×10-6),并具有明显的负Eu异常(Eu/Eu*分别为0.01～0.02,0.57～0.72),另外,正长花岗岩相对二长花岗岩明显地富集大离子亲石元素(Rb、Th、K)及高场强元素(Zr、Hf、Nb),而强烈亏损Ba、Sr、Eu、Ti等,具有较高的10000Ga/Al比值(>2.44)。依据微量元素比值及相关判别图,可将接特布调花岗岩体进一步细分为A1型和A2型。接特布调岩体就位于后碰撞环境,来源于由年轻的地幔来源物质组成的下地壳。在后碰撞岩浆活动的初期,年轻的下地壳部分熔融形成具有岛弧印迹的A2型二长花岗岩岩浆,随着岩石圈进一步伸展,可能在局部出现类似裂谷的环境,即形成显示裂谷特征的A1型正长花岗岩岩浆。Late Paleozoic post-collisional granitoids are widespread in West Junggar and even in the whole northern Xinjiang. As a representative of these intrusions, the Jietebutiao granite occurs in the southwestern margin of West Junggar, mainly comprises middle-coarse-grained monzogranite and syenogranite, and provides important clues for petrogenesis of granites and evolution of tectonic-magmatism in West Junggar. This paper reports the results of high-precision zircon LA-ICP-MS U-Pb dating of the Jietebutiao granite, which yields weighted mean 206pb/Z38U ages of （287±9） Ma （n=10, MSWD=0.92）and （278±3） Ma （n=14, MSWD=0.43）for monzogranite and syenogranite, respectively, corresponding to the Early Permian and implying that the granite is the product of post-collisional magmatic activity around the Junggar area approximately at 300 Ma. Petrogeochemical analyses suggest that the Jietebutiao pluton which has long been thought to be of I-type granite actually belongs to A-type. The syenogranite is characterized by high silica （SiO2： 76.11%-76.82%）, alkali （Na20＋K20： 8.47%-8.49%）, and low titanium and calcium （TiO2： 0.04%-0.05%, CaO： 0.36%-0.42%）. Moreover, the monzogranite is similar to the syenogranite in such aspects as high silica （SiO2： 68.35%-71.80%） and alkali （Na20＋K20： 6.80%-7.86%） as well as low titanium and calcium （TiO2： 0.29%-0.82%, CaO： 1.76%-2.87%）; nevertheless, they both belong to metaluminous or peraluminous （ACNK： 0.98-1.09） high-K talc-alkaline series. Compared with the monzogranite, the syenogranite has relatively low REE content （EREE： 23.8x 10-6-49.3x 10-6, 95.23x10-6-222.2x10-6） with significant negative Eu anomalies （Eu/Eu＊： 0.01-0.02, 0.57-0.72）. They are also enriched with large ion lithophile elements such as Rb, Th and K and high strength field elements such as Zr, Hf and Nb and strongly depleted in Ba, Sr, Eu and Ti, with high 10000Ga/A1 ratios （〉2.44）. These characteristics are more clearly in syenog

关 键 词：A型花岗岩 锆石LA—ICP—MS U—Pb定年 岩石地球化学 岩石成因 后碰撞 西准噶尔 

分 类 号：P588.121[天文地球—岩石学]