地质学报2018，Vol.92Issue(4)：747-768,22.
赣西北麦斜岩体锆石U-Pb年代学、地球化学以及Sr-Nd同位素研究及其岩石成因
Zircon U-Pb Geochronology, Geochemistry, and Sr-Nd Isotopic Characteristics of the Maixie Biotite-Granodiorite Pluton in Northwestern Jiangxi Province and Their Implications for Petrogenesis
摘要
Abstract
Maixie pluton is composed predominantly of light-gray,fine-to medium-grained,equigranular biotite granodiorite.LA-ICP-MS zircon U-Pb dating yielded two weighted mean 206Pb/238U ages of 433.4±7.1Ma (MSWD=0.82) and 431.8±6.0 Ma (MSWD=0.43) for the Maixie pluton,indicating that it was the product of magmatic activities in the Early Paleozoic.The Maixie granodiorites contain minor amount of amphiboles.Geochemical analysis shows that the pluton is characterized by high SiO2 (62.0％～71.43％)and high K2O/Na2O(0.88～2.42) (with a total alkali (K2O+Na2O)=5.39％ ～8.12％),and low Fe2O3 (2.61％ ～5.70％),MgO(0.96％ ～2.90％),CaO(1.39％ ～5.11％),TiO2 (0.27％ ～0.67％) and P2O5 (0.06％ ～0.10％),with weak peraluminium (A/CNK=0.98～1.25,with an average value of 1.08).There exists a clear negative correlation between SiO2 and P2O6.All these features suggest that the Maixie granodiorites belong to high-K calc-alkaline Ⅰ-type granite.The trace element studies show an enrichment of Rb,Th,LREE and depletion of Nb,Ta,Ti,P,Ba,Sr and other elements,with distinct LREE and HREE fractionation of (La/Yb)N =5.00～40.42 (a mean of 16.97) and weak to medium Eu negative anomalies of δEu =0.63 ～ 1.00 (an average of 0.77).Homogeneous Sr-Nd isotopic compositions { (87 Sr/86 Sr)i=0.708667～0.709175,εNd(t) =7.57～-7.29,TDM2 =1.75～1.87Ga (a mean of 1.81Ga)},relatively high (87 Sr/86 Sr)Ⅰ ratios and negative εNd (t) values with two-stage Nd mode ages of Paleoproterozoic suggest that the Maixie granodiroites generated by partial melting of the Paleoproterozoic crust.Experimental petrology and geochemical characteristics of our studied samples show that the Maixie biotite granodiorites resulted from water-unsaturated partial melting of the intermediate-mafic rocks (e.g.,amphibolite) in the lower-to middle-crust,with addition of a certain content of mantle-derived materials at the initial stage of magmas,and extensive fractional crystallization of amphibole,biotite,ilmenite,titanite,plagioclase and apatite.The mantle-derived materials were the product of partial melting of the Paleoproterozoic subduction-modified lithospheric mantle in South China.Combined with regional geological background and published data,this study suggests that that the Maixie pluton was formed in a post-collisional introcontinental environment,and partial melting of early Paleozoic early Paleozoic lower crust in South China due to underplating of mantle-derived magmas resulted in extensive distribution of intracontinental magmatic rocks.关键词
麦斜岩体/华南/早古生代/Ⅰ型花岗岩/Sr-Nd同位素Key words
Maixie pluton/South China/early Paleozoic/Ⅰ-type granite/Sr-Nd isotopes引用本文复制引用
王帅,陶继华,李武显,王安东,吕璞良..赣西北麦斜岩体锆石U-Pb年代学、地球化学以及Sr-Nd同位素研究及其岩石成因[J].地质学报,2018,92(4):747-768,22.基金项目
本文为国家自然科学青年基金(编号:41303020)、同位素地球化学国家重点实验室(中国科学院广州地球化学研究所)(编号:SKLIG-KF-13-06)、东华理工大学核资源与环境国家重点实验室培育基地自主基金(编号:Z1606),东华理工大学博士科研启动基金(编号:DHBK2012208)和国家留学基金(CSC201608360054)资助成果. （编号:41303020）
