南天山盲起苏花岗岩体的成因及构造意义:来自年代学、地球化学及Nd-Hf同位素证据  

Genesis and tectonic significance of the Mangqisu pluton in the South Tianshan:evidence from geochronology,geochemistry,and Nd-Hf isotopes

作　　者：于新慧 秦切 黄河[2] 王涛[2] 张招崇[1] 童英[2] 郭磊[2] 宋鹏[2] YU Xinhui;QIN Qie;HUANG He;WANG Tao;ZHANG Zhaochong;TONG Ying;GUO Lei;SONG Peng(China University of Geosciences(Beijing)School of Earth Sciences and Resources,Beijing,100083;Institute of Geology Chinese Academy of Geological Sciences,Beijing,100037)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2020年第10期2893-2918,共26页Acta Geologica Sinica

基　　金：NSFC新疆联合基金重点支持项目(项目编号:U1403291);中国地质调查局二级项目(DD20190001)联合资助的成果。

摘　　要：南天山造山带位于中亚造山带与塔里木克拉通的接壤地带,是了解克拉通及造山带构造演化的重要地区。但就南天山洋最终闭合和陆陆碰撞的时代目前还存在不同观点。盲起苏花岗岩体位于南天山造山带东段,是该区大型的复式花岗岩体,主要由东部黑云母花岗闪长岩、西部黑云母花岗岩和中部二云母花岗岩组成。LA-ICP-MS锆石U-Pb定年结果显示,东部、西部和中部花岗岩的形成年龄分别为297±4 Ma、294±3 Ma和292±2 Ma。地球化学特征上,东部和西部花岗岩的SiO2含量为65.34%~73.12%,A/CNK为1.00~1.11(平均1.05),Na2O+K2O的含量为7.26%~8.52%,属高钾钙碱性弱过铝质岩石;中部花岗岩的SiO2含量为71.97%~72.84%,A/CNK为1.09~1.14(平均1.12),Na2O+K2O的含量为8.36%~8.80%,属钙碱性强过铝质岩石。稀土元素上,三者均富集轻稀土元素\[(La/Yb)N=9.58~44.94\],亏损重稀土元素(HREE,LREE/HREE=8.00~22.97),并呈现不同程度的Eu负异常(东部δEu=0.67~0.81;西部δEu=0.48~0.78;中部δEu=0.44~0.48)。微量元素上,三者均富集大离子亲石元素(K、Rb、Ba),亏损高场强元素(Nb、Ta、Ti)。同位素特征上,锆石εHf(t)值分别为-11.31^-1.64(东部)、-5.41^-0.50(西部)和-14.43^-2.51(中部),二阶段Hf模式年龄(tDM2)均在1.30~2.20 Ga之间;东部岩体的εNd(t)的值为-6.92^-10.10,二阶段模式年龄tDM2(Nd)在1.62~1.88 Ga之间。综合区域地质和前人研究资料,表明盲起苏复式花岗岩体可能是后碰撞早期阶段由加厚的变质火成岩地壳发生部分熔融,经不同程度结晶分异所形成的,并暗示了南天山洋的闭合及陆陆碰撞的时间应发生于二叠纪之前。The southTianshan orogenic belt,located on the border between the Central Asian Orogenic Belt and the Tarim Craton,is an important area for understanding the tectonic evolution of craton and orogenic belt.However,there are still different views about the timing of closure of the southern Tianshan Ocean and the collision between plates.The Mangqisu pluton is a large composite granite pluton belonging to the eastern part of the South Tianshan Orogenic Belt,and consists mainly of biotite granodiorite unit in the east,biotite granite unit in the west,and two mica granite units in the central part.Our new zircon U-Pb(LA-ICP-MS)results assign emplacement ages of the eastern,western and central units of 297±4 Ma,294±3 Ma and 292±2 Ma,respectively.Geochemically,samples from eastern and western parts of the pluton show SiO2 ranging from 65.34%~73.12%,A/CNK(1.00~1.11,the average is 1.05),moderate Na2O+K2O(7.26%~8.52%),are of high-K calc-alkaline and weakly peraluminous series.The central granite unit has SiO2 ranging from 71.97%~72.84%,(A/CNK=1.09~1.14,with an average of 1.12),Na2O+K2O(8.36%~8.80%),suggesting that they are of calc-alkaline and strong peraluminous series.They are enriched in LREE((La/Yb)N=9.58~44.94),depleted in HREE(LREE/HREE=8.00~22.97),and exhibit negative Eu anomalies,withδEu ranging from 0.67 to 0.81 in the eastern unit,from 0.48 to 0.78 in the western unit,and from 0.44 to 0.48 in the central unit.According to their trace element patterns,the studied rocks are enriched in large ion lithophile elements(K,Rb,Ba)and depleted in high field-strength element(Nb,Ta,Ti).The zircon Hf isotopic data of the eastern,western and central units of the Mangqisu pluton showεHf(t)range from-11.31 to-1.64,-5.41 to-0.50,and-14.43 to-2.51,respectively while the two-stage model age(tDM2(Hf))varies from 1.30 Ga to 2.20 Ga.According to the Sr-Nd isotope data,theεNd(t)value of the eastern section ranges from-6.92 to-10.10,and the two-stage model age(tDM2(Nd))varies from 1.88 Ga to 1.62 Ga.Combined with regional geologic

关 键 词：南天山 晚古生代 花岗岩 后碰撞 结晶分异 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]