安庆早白垩世洪镇花岗岩成因及其对基底构造格局的启示  

Petrogenesis of the Early Cretaceous Hongzhen granite in Anqing area and its implication for the basement structure

作　　者：闫峻[1] 宋庆尧 刘建敏[1] 谢建成[1] 汪志杰 YAN Jun;SONG Qingyao;LIU Jianmin;XIE Jiancheng;WANG Zhijie(School of Resource and Environmental Engineering,Hefei University of Technology,Hefei,230009)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《地质论评》2023年第6期2032-2046,共15页Geological Review

基　　金：国家自然科学基金资助项目(编号:42030801)的成果。

摘　　要：花岗岩可以有效示踪大陆基底物质,并区分具有不同地壳结构和演化历史的构造块体。洪镇花岗岩位于长江中下游地区江北A型花岗岩带的西延位置,距离郯庐断裂带约30 km。锆石SIMS定年表明,安庆怀宁县洪镇花岗岩形成于126.2±2.0 Ma,与长江中下游A型花岗岩以及大别造山带I型花岗岩的形成时代一致。洪镇花岗岩高硅、富钾,属于高钾钙碱性系列I型花岗岩。其富集轻稀土元素和大离子亲石元素,相对亏损中稀土元素和高场强元素,经历了角闪石为主的结晶分异。洪镇花岗岩具有较为富集的Sr—Nd—Hf同位素,和低放射性成因Pb同位素组成,其n(^(87)Sr)/n(^(86)Sr)(t)为0.7065~0.7066,ε_(Nd)(t)值为-10.9~-12.0,锆石ε_(Hf)(t)为-6.7~-13.2,n(206Pb)/n(^(204)Pb)(t)、n(^(207)Pb)/n(^(204)Pb)(t)和n(^(208)Pb)/n(^(204)Pb)(t)分别在17.063~17.109、15.568~15.572和37.351~37.373之间。综合研究表明,洪镇花岗岩起源于古—中元古代中低成熟度沉积岩的水致部分熔融,为幔源岩浆底侵导致。从物质来源上,洪镇花岗岩岩浆源区类似于大别造山带经历过俯冲、折返后的中上地壳,而显著不同于长江中下游同时代A型花岗岩源区,表明洪镇地区具有上下地壳分属长江中下游和大别造山带的构造属性。在早白垩世早期郯庐断裂带南段西盘向南的强烈挤压下,大别造山带下地壳发生不规则流动,越过郯庐断裂带进入到洪镇地区下地壳成为洪镇花岗岩的源区。Objectives:In order to explore petrogenesis of the early Cretaceous Hongzhen granite in Huaining County,Anqing City,Anhui Province,and further confirm geochemical characteristics of the magma source,as well as reveal the special basement structure in this area of close to the Tancheng-Lujiang Fault.Methods:Combined with field work and microscope observation,analysis of the SIMS zircon U-Pb isotopic dating,XRD major elements,ICP-MS trace elements,TIMS Sr-Nd-Pb isotopes,and LA-MC-ICPMS zircon Hf isotope are carried out.Results:The SIMS zircon U-Pb dating confirms that the Hongzhen granite was formed at 126.2±2.0 Ma.This granite has characteristics of high silicon and potassium,and is I-type granite,belonging to high potassium calcalkaline series.It also shows enrichment of light rare earth elements and large ion lithophile elements,depletion of middle rare earth elements and high field strength elements.The Hongzhen granite has enriched Sr-Nd-Hf isotopic and low radiogenic Pb isotopic compositions,with^(87)Sr/^(86)Sr(t)of 0.7065~0.7066,ε_(Nd)(t)of-10.9~-12.0,zirconε_(Hf)(t)of-6.7~-13.2,206Pb/^(204)Pb(t)of 17.063~17.109,^(207)Pb/^(204)Pb(t)of 15.568~15.57,and^(208)Pb/^(204)Pb(t)of 37.351~37.373.Conclusions:The Hongzhen granite formed at 126.2±2.0 Ma,which is simultaneous with the A-type granites form the Middle-Lower Yangtze River region and the I-type granites from the Dabie Orogen.It was derived from hydrothermal partial melting of the Paleo-Mesoproterozoic sedimentary rock with middle-low degree of maturity,induced by underplating of mantle derived magma,and experienced fractionation of dominant amphibole.Concerning the magma source,the Hongzhen granite is similar to the homochronous granites from the Dabie Orogen,and quite different from the homochronous A-type granites in the Middle-Lower Yangtze River region,indicating that the upper and lower crusts beneath the Hongzhen area have different tectonic affinities.During early stage of early-Cretaceous,the west wall of the southern Tan-Lu Fault suffered strong

关 键 词：花岗岩 同位素 锆石定年 基底 安庆洪镇 长江中下游 

分 类 号：P534.53[天文地球—古生物学与地层学] P588.121[天文地球—地质学] P597.3