华北克拉通南缘A型花岗岩的年代学和Nd-Hf同位素组成:对古元古代晚期伸展事件的制约  

The geochronology and Nd-Hf isotope compositions of A-type granites on the southern margin of North China Craton:Constraints on the Late Paleoproterozoic extensional events

作　　者：师江朋 杨德彬[1] 霍腾飞[1] 杨浩田[1] 许文良[1] 王枫[1] SHI JiangPeng YANG DeBin HUO TengFei YANG HaoTian XU WenLiang WANG Feng(College of Earth Sciences, Jilin University, Changchun 130061, China)

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2017年第10期3042-3056,共15页Acta Petrologica Sinica

基　　金：教育部新世纪优秀人才计划(NCET-12-0237);国家自然科学基金项目(41472052);中央高校基本科研业务费;吉林大学研究生创新基金资助项目(2016195)联合资助

摘　　要：河南上店和登封古元古代晚期A型花岗岩的锆石LA-ICP-MS U-Pb年代学、岩石地球化学和Nd-Hf同位素研究为讨论华北克拉通南缘中部古元古代晚期构造演化提供了依据。结果表明,上店花岗斑岩和登封正长花岗岩中锆石发育振荡生长环带,结合高的Th/U比值(0.36~1.64),表明其为岩浆成因,岩浆锆石的207Pb/206Pb加权平均年龄分别为1801Ma、1801Ma和1795Ma,即它们形成于古元古代晚期;上店花岗斑岩具有高SiO_2(70.30%~71.83%)、富碱(K2O+Na2O=8.76%~11.01%)、贫Ca O(0.18%~0.36%)、P2O5(0.12%~0.15%)和MgO(0.02%~0.20%)的特征,富集LILEs(Cs、Rb、Ba和K)、贫HFSEs(Nb、Ta、Zr和Hf)和强烈亏损Sr、P、Ti元素,具有负的Eu异常(δEu=0.44~0.59),结合高的FeOT/(FeOT+MgO)比值(0.94~1.00)和10000×Ga/Al比值(2.70~3.74),暗示其为A型花岗岩,具造山后A2型花岗岩特征;上店花岗斑岩的全岩εNd(t)值变化于-8.94^-6.87之间,tDM2=3243~3049Ma,锆石εHf(t)值介于-14.1^-6.5之间,tDM2=3030~2655Ma;登封正长花岗岩的锆石εHf(t)值介于-11.3^-8.4之间,tDM2=2887~2744Ma。上述结果暗示,上店和登封A型花岗岩均来源于幔源岩浆底侵作用下的中-新太古代基底物质的部分熔融,形成于华北克拉通东部和西部陆块碰撞造山后的伸展环境。A combined LA-ICP-MS zircon U-Pb geochronology,whole-rock geochemistry and Nd-Hf isotope study of Shangdian and Dengfeng granites in Henan Province provides the insights to discuss the Late Paleoproterozoic tectonic evolution of central southern margin of North China Craton（NCC）.Zircons from the Shangdian and Dengfeng granites show oscillatory CL zoning and high Th/U ratios（0.36~1.64）,indicative of a magmatic origin.The weighted mean of concordant ^207Pb/^206Pb ages for three plutons yielded ages of 1801 Ma,1801 Ma and 1795 Ma,respectively,indicating they formed in the Late Paleoproterozoic.The Shangdian granites have high contents of SiO2（70.30%~71.83%）,total-alkali（K2O＋Na2O=8.76%~11.01%）,and low amounts of CaO（0.18%~0.36%）,P2O5（0.12%~0.15%）,MgO（0.02%~0.20%）.Additionally,they show enrichment of LILEs（Cs,Rb,Ba,and K）and depletion of HFSEs（Nb,Ta,Zr,and Hf）,Sr,P and Ti.They exhibit prominent negative Eu anomaly（δEu=0.44~0.59）,high ratios of FeO^T/（FeO^T＋MgO）（0.94~1.00） and 10000×Ga/Al（2.70~3.74）,suggesting that they are A-type granites,further belonging to the A2-type granites formed in a post-collisional environment.The whole-rock εNd（t） values of Shangdian granites range from-8.94 to-6.78 and two-stage model ages（tDM2） range from 3243 Ma to 3049 Ma.Zircons from Shangdian granites haveεHf（t） values ranging from-14.1 to-6.5,corresponding to tDM2=3030~2655 Ma.Similarly,zircons from Dengfeng granites haveεHf（t） values ranging from -11.3 to -8.4,corresponding to tDM2=2887~2744 Ma.The above results imply that Shangdian and Dengfeng granites were dominantly derived from partial melting of Meso-Neoarchaean crystalline basement materials caused by the underplating of mafic magmas,and were formed in a post-collisional extensional tectonic setting related to the collision between the Eastern Block and Western Block of NCC.

关 键 词：古元古代 A型花岗岩 U-PB年代学 地球化学 华北克拉通南缘 

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