地质学报2017，Vol.91Issue(6)：1227-1244,18.
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
摘要
Abstract
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％),lowMgO (0.6％～0.9％),P2O5(0.06％～0.11％),TiO2(0.39～0.58％) andFeOT(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 calcalkaline 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 mantle magma.These features of the monzogranite are consistent with that of the Early Paleozoic arc-type magmatic rocks in North Qilian.Therefore,our research provides new evidence that North Altyn was the western extensional part of the North Qilian.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Key words
Monzogranite/Geochemistry/Zircon SHRIMP U-Pb dating/Hf isotope/North Altyn引用本文复制引用
吴玉,陈正乐,陈柏林,王永,孟令通,何江涛,王斌,韩梅梅..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[J].地质学报,2017,91(6):1227-1244,18.基金项目
本文由“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)和国土资源部公益行业科研专项(201411024-3)联合资助. （编号:2011BAB06B08-04）
