鄂东南地区殷祖岩体的成因及其地质意义:年代学、地球化学和Sr-Nd-Hf同位素证据  

Petrogenesis and Implications of the Yinzu Pluton in Southeast Hubei Province:Evidence from Geochronology,Geochemistry,and Sr-Nd-Hf Isotopes

作　　者：丁丽雪[1,2] 黄圭成[1,2] 夏金龙[1,2] 

机构地区：[1]中国地质调查局武汉地质调查中心,武汉430205 [2]中国地质调查局花岗岩成岩成矿地质研究中心,武汉430205

出　　处：《地质学报》2017年第2期362-383,共22页Acta Geologica Sinica

基　　金：中国地质调查局地质调查项目(编号1212011120863&12120114005901)资助的成果

摘　　要：殷祖岩体是鄂东南地区六大岩体之一,也是目前该地区唯一不成矿的大岩体。LA-ICP-MS锆石UPb年代学数据显示,殷祖岩体至少有两次岩浆侵位活动。该岩体的主体岩性为石英闪长岩,侵位于148±1 Ma,早期黑云角闪辉长岩侵位于151±1 Ma。这一研究结果表明,鄂东南地区乃至长江中下游地区中生代的岩浆活动在~150 Ma时已经开始。根据野外侵入接触关系及元素地球化学特征,殷祖岩体的岩石类型大致可以分为两组:第一组为闪长-辉长岩类,包括闪长岩、黑云辉长岩和黑云角闪辉长岩,具有低SiO_2,低Ba、Sr含量,高TiO_2、FeOT、MgO及Y、Yb含量;第二组包括石英闪长岩和花岗闪长斑岩,具有高SiO_2,高Ba、Sr含量,低TiO_2、FeOT、MgO及Y、Yb含量。石英闪长岩的(87Sr/86Sr)i和εNd(t)值分别为0.70638~0.70719和-9.56^-7.59,锆石εHf(t)值为-10.21^-1.15,Nd-Hf同位素基本耦合;黑云角闪辉长岩的(87Sr/86Sr)i和εNd(t)值分别为0.70742和-9.79,锆石εHf(t)值为-24.58^-15.22,Nd-Hf同位素出现解耦。综合两期岩浆活动的侵位时间、地球化学以及Sr-NdHf同位素特征,推测它们可能是同一岩浆源区演化的产物,即均主要来源于富集岩石圈地幔。分离结晶作用在主体岩性石英闪长岩的形成过程中起了主导作用。早期小规模的辉长岩类出现Nd-Hf同位素解耦现象可能与石榴子石效应有关。The Yinzu pluton,one of the six large intrusions in southeastern Hubei Province,is the only barren large intrusion in the region.LA-ICPMS zircon U-Pb dating results show that the Yinzu pluton experienced at least two episodes of magmatism.The pluton is composed mainly of quartz diorites and was emplaced in 148±1 Ma,with the early biotite hornblende gabbro emplaced at 151±1 Ma.The study indicates that the Mesozoic magmatic activities in southeastern Hubei Province and even the Middle and Lower Yangtze River began in ca.150 Ma.Based on their contact relation in the field and element chemical characteristics,the rock types of the Yinzu pluton can be divided into two groups.The first is dioritegabbro,including diorite,biotite gabbro and biotite hornblende gabbro,which have low SiO2,Ba,Sr and high TiO2,FeOT, MgO,Y and Yb contents.The second includes quartz diorite and granodiorite porphyry,which have high SiO2,Ba,Sr and low TiO2,FeOT,MgO,Y and Yb contents.（87Sr/86Sr）iandεNd（t）values of quartz diorite are 0.70638-0.70719and-9.56--7.59,separately,which are coupled with zirconεHf（t）values ranging from-10.21to-1.15.（87Sr/86Sr）iandεNd（t）and of biotite hornblende gabbro are 0.70742and-9.79,separately,and zirconεHf（t）values vary from-24.58to-15.22,showing that Nd and Hf isotopic compositions are decoupled.Combined with emplacement time and geochemical and Sr-Nd-Hf isotopic characteristics of two magmatic activities,it can be inferred that the pluton should be evolvement products of the same magmatic source area,i.e.from enriched lithospheric mantle.Fractional crystallization played a dominant role in the formation of quartz diorite.Nd-Hf isotope decoupling of the early small scale gabbros is probably related to the effect of garnet.

关 键 词：鄂东南地区 殷祖岩体 锆石U-PB年龄 黑云角闪辉长岩 Nd-Hf同位素解耦 

分 类 号：P597.3[天文地球—地球化学] P587[天文地球—地质学]