摘要
对湖南雪花顶岩体花岗岩和包体的主量元素、微量元素、稀土元素及Sr-Nd同位素进行了分析。研究表明,包体为弱过铝高钾钙碱性-钙碱性石英闪长质-花岗闪长质岩石,寄主岩石为偏铝质高钾钙碱性黑云母二长花岗岩。两者具有比较相似的地球化学特征:在微量元素上,均表现为富集大离子亲石元素,相对亏损相容元素场Cr、Ni和高场强元素Nb、Ta、P等,具明显的Nb、P、Ti、Ba、Sr负异常;在稀土元素上,均表现为轻稀土富集,轻重稀土呈较强的分馏并具有中等的Eu负异常;包体的εSr(t)、εNd(t)值变化在207.0～247.7、-5.8～-7.8之间,寄主岩石的εSr(t)、εNd(t)值变化在214.9～236.6、-7.9～-8.6之间,均具有地壳的典型组成。在此基础之上,结合岩石形貌学、矿物学研究,本文认为雪花顶岩体中包体为寄主岩石源区的花岗质岩浆的残留体。再综合区域加里东花岗岩的地球化学特征,进一步认为雪花顶花岗岩为挤压向伸展松弛转换环境下早元古代晚期地壳物质重熔的产物,诱导因素可能为加里东早期沿赣东北、湘南、粤西一线发生的地幔物质底侵事件。部分熔融过程中没有新生地幔物质的加入。源区物质主要以长石质陆源沉积物为主,含有较多的中-基性岛弧成分;其成熟度可能较低,推测形成于活动大陆边缘环境。
We report the major elements, trace elements, rare earth elements and Sr-Nd isotopic compositions of the Xuehuading granite batholith and its enclaves to constraint the magma source and geodynamic setting of this Caledonian intrusion in South China. The major elements compositions show the enclaves are weakly peraluminous high-K calc-alkaline or calc-alkaline dioritic-granodioritie rocks, while the host rocks are metaluminous high-K ealc-alkaline biotite monzogranites. The geochemical characteristics of the granite batholith and its enclaves indicate both of them originated from the crust. They are rich in both large ion lithophile elements and light rare earth elements, relatively depleted in Ba, Sr and high field strength elements such as Nb, Ta, P, etc. , moderately fractionated between light and heavy rare earth elements. The εSr（t） of enclaves varies from 207.0 to 247.7 and εNd（t） from -5.8 to -7.8, correspondingly with 214.9 ～236.6 and -7.9 ～ -8.6 for host rocks. The geochemical evidences, field observation and petrography indicate that the enclaves are partial melting restites when the Xuehuading granitic magma were formed in the source region： Further integrating with geochemical characteristics of regional Caledonian granites, we propose that the Xuehuading granites are anatectite derived by partial melting of the immature crust materials, which probably induced by a magma underplating event along the area from northeastern Jiangxi, through southern Hunan, to western Guangdong. No mantle material involved in the anatectite. Source materials mainly consist of feldspathic terrigenous sediments deposited in an active continental margin in late Paleoproterozoic, many intermediate-mafic island arc materials also added in during deposition. The Xuehuading granitic magma intrusion were formed under a geodynamic setting of the transition from compression to extension in the Caledonian orogeny of South China.
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2009年第4期588-597,共10页
Geotectonica et Metallogenia
基金
中国地质调查局地质大调查项目(1212010533307和1212010813061)资助
关键词
花岗岩
包体
地球化学特征
成因
雪花顶
湖南
geochemical characteristics
petrogenesis
Xuehuading granite
enclaves
south China
