赣西北麦斜岩体的成因：地球化学、锆石U-Pb年代学及Hf同位素制约  

Petrogenesis of the Maixie Pluton in Northwest Jiangxi Province:Constraints from Petrochemistry,Zircon U-Pb Chronology and Hf Isotope

作　　者：农军年[1,2] 钟玉芳[3] 刘 磊[2] 刘园园[2] 熊富浩[2] 邹 瑜[4] 

机构地区：[1]广西地质勘查总院,南宁530023 [2]中国地质大学研究生院,武汉430074 [3]中国地质大学地球科学学院,武汉430074 [4]中国地质大学资源学院,武汉430074

出　　处：《地质科技情报》2012年第2期9-18,共10页Geological Science and Technology Information

基　　金：国家自然科学基金(40872053);中国地质调查局地质矿产调查评价专项(基[2010]矿评01-17-14)

摘　　要：对麦斜岩体2个代表性样品进行LA-ICP-MS锆石U-Pb测年,获得206Pb/238 U加权平均年龄分别为(434±2)Ma和(437±2)Ma,说明该岩体形成于加里东期。麦斜花岗闪长岩为高钾钙碱性、准铝Ⅰ型花岗岩,具有高Ba-Sr花岗岩的地球化学特征,其w(Ba)(838～1 171μg/g)、w(Sr)(346～485μg/g)高,w(Y)(<19μg/g)、w(Yb)(<1.8μg/g)及w(Rb)/w(Sr)比值(平均为0.37)低,具有弱的Eu负异常,亏损Nb、P、Ti等高场强元素。锆石的εHf(t)值变化范围在-35.32～-1.50之间,二阶段模式年龄(T2DM)在3.63～1.51Ga之间,指示花岗岩主要来自中元古-古元古代古老地壳,并有年青幔源组分的参与。结合岩体的化学组成、锆石Hf同位素的不均匀性及微粒闪长质包体发育状况,推测麦斜岩体主要由基性下地壳部分熔融形成,岩浆形成过程中有幔源基性岩浆和表壳物质的加入。In this paper,two representative samples of Maixie pluton were selected for LA-ICP-MS zircon U-Pb dating,yielding U-Pb ages of（434±2）Ma and（437±2）Ma,which indicates that the Maixie granites were formed in Caledonian orogen.Whole-rock geochemical data indicate that the rocks belong to high-K calc-alkaline series,they are typical metaluminous I-type granite,with some features similar to those of the high Ba-Sr granite,i.e.,high content of Ba and Sr and high ratios of Sr/Y and La/Yb,but low content of Y（19 μg/g） and Yb（1.8 μg/g） and low ratios of K/Rb and Rb/Sr（average 0.37）.Besides,the rocks show negative Eu anomaly,and are depleted in high field strength elements,such as Nb,P,Ti and so on.The Hf isotopic compositions of zircons show that the rocks have εHf（t） values of-35.32 to-1.50 and T2DM（Hf） model ages ranging from 3.63 to 1.51 Ga,implying that the magma was derived from Paleo-or Meso-Proterozoic rocks,with involvement of some jurenile mantle in petrogenesis.Combined with the geochemical composition,the inhomogenous zircon Hf isotopic compositions as well as the appearance of common mafic microgranular enclaves,we suggest that the Maixie pluton were formed by magma mixing between the mafic magmas and felsic magmas generated by partial melting of overlying lower crust inducing mafic magmas.

关 键 词：锆石U-PB定年 HF同位素 加里东期 麦斜岩体 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]