北阿尔金喀腊大湾南段二长花岗岩地球化学、SHRIMP锆石U-Pb年代学、Hf同位素特征及其对壳-幔相互作用的指示  

Geochemistry,Zircon SHRIMP U-Pb Dating and Hf Isotopic Compositions of the Monzogranite from the Southern Kaladawan of North Altyn and Their Implications for Crust-Mantle Interaction

作　　者：吴玉[1,2] 陈正乐[2,3] 陈柏林[2] 王永[2] 孟令通[2] 何江涛[2,4] 王斌[4] 韩梅梅[2,4] 

机构地区：[1]核工业北京地质研究院,北京100029 [2]中国地质科学院地质力学研究所,北京100081 [3]东华理工大学,南昌330013 [4]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地质学报》2017年第6期1227-1244,共18页Acta Geologica Sinica

基　　金："十二.五"国家科技支撑计划项目(编号:2011BAB06B08-04);国家自然科学基金(编号:U1403292;41502086);国土资源部公益行业科研专项(201411024-3)联合资助

摘　　要：喀腊大湾位于北阿尔金山的中东段,区内分布有大量早古生代中-酸性侵入岩体,这些岩体为探索北阿尔金早古生代构造-岩浆活动及其区域构造演化提供了重要依据。本文对出露在喀腊大湾南段的二长花岗岩展开了详细的锆石SHRIMP U-Pb年代学、全岩地球化学和锆石Hf同位素分析。锆石SHRIMP U-Pb定年获得二长花岗岩的成岩年龄为484.2±4.9Ma(MSDW=0.46,n=14),属早奥陶世。在地球化学组成上,二长花岗岩具有富碱(全碱8.31%~8.66%)、高钾(K_2O=3.65%~4.76%)和贫MgO(0.6%~0.9%)、P_2O_5(0.06%~0.11%)、TiO_2(0.39%~0.58%)和FeOT(1.82%~2.34%)的特征,岩石铝饱和指数(A/CNK)为0.96~1.01,属准铝质-弱过铝质高钾钙碱性Ⅰ型花岗岩。二长花岗岩具有弱的正Eu异常,明显富集大离子亲石元素(如K、Rb、Ba、Th、U)和LREE,相对亏损高场强元素(如Ti、Ta、Nb)和HREE,显示出弧岩浆岩的地球化学特征。锆石Hf同位素分析结果表明,二长花岗岩的ε_(Hf)(t)均为正值(+4.08^+8.26),且变化范围较小,对应的二阶段模式年龄(tDM2)为875~1099Ma,反映成岩过程中有显著的幔源新生地壳物质加入。综合区域地质背景及前人研究成果,认为喀腊大湾南段二长花岗岩应形成于北阿尔金洋向南侧阿中地块俯冲消减的活动大陆边缘弧环境,其岩浆源区可能起源于新生地壳和古老基底地壳构成混合地壳的部分熔融,岩体在形成过程中经历了壳幔岩浆混合作用,这些特征与北祁连早古生代形成于俯冲消减背景下的中-酸性侵入岩体相似,进而为北阿尔金曾是北祁连的西延部分提供了新的佐证。Large-scale Early Paleozoic intermediate-felsic granitic plutons are distributed at Kaladawan in the middle-eastern segment of North Altyn, and provide important evidence for understanding early Paleozoic tectonic-magmatic activities and regional tectonic evolution in North Altyn. In this paper, the monzogranite exposed in southern Kaladawan was analyzed using zircon SHRIMP U-Pb dating, whole rock geochemistry and Hf isotopes. Zircon SHRIMP U-Pb dating yields an age of 484.2 ± 4.9 Ma （MSDW = 0.46） for the monzogranite, suggesting its emplacement in Early Ordovician. The monzogranite is geochemically characterized by high K2O （365%～476%） and alkali （Na2O＋K2O=831%～866%）, low MgO （06%～09%）, P2O5 （006%～011%）, TiO2 （039%～ 058%） and FeOT （1.82%～2.34%）, with A/CNK values ranging from 0.96 to 1.01, suggesting that it can be classified as the high K calc alkaline and metaluminus weak peraluminous I type granite. The primitive mantle normalized trace element patterns and chondrite normalized REE diagrams of monzogranite show obvious enrichment in LILEs （such as K, Rb, Ba, Th, U） and LREE, depletion in HFSEs （such as Ti, Ta, Nb, P） and HREE, with slight positive Eu anomalies, revealing the arc magma affinity. In situ zircon Hf isotope data display that the monzogranite has depleted Hf isotopic compositions with positive εHf（t） values （＋4.08 to ＋8.26） and young tDM2 （875～1099 Ma）, reflecting that mantle derived juvenile crust plays a significant role in the magmatic process. Together with the tectonic regime of the monzogranite and previously published data, we suggest that the monzogranite probably formed in an active continental arc setting related to southward subduction of the North Altyn Ocean during the Early Paleozoic. The magma likely originated from partial melting of hybrid crust consisting of mantle derived juvenile crust and ancient continental crust, suggesting that the rock experienced mixing of crustal and mantl

关 键 词：二长花岗岩 地球化学 锆石SHRIMP U-Pb年龄 Hf同位素 北阿尔金 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]