湖南雪花顶花岗岩及其包体的地质地球化学特征和成因分析
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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-granodioritic rocks,while the host rocks are metaluminous high-K calc-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.
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-granodioritic rocks,while the host rocks are metaluminous high-K calc-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.
引文
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陈懋弘,梁金城,张桂林,李文杰,潘罗忠,李荣森.2006.桂北-桂东加里东期盆地构造沉降史分析.大地构造与成矿学,30(1):9-17.
杜杨松.1994.火成岩中下地壳岩石包体的特征及其研究意义.地质科技情报,13(3):33-39.
付建明,马昌前,谢才富,张业明,彭松柏.2004.湖南九嶷山复式花岗岩体SHRIMP锆石定年及其地质意义.大地构造与成矿学,28(4):370-378.
付建明,谢才富,彭松柏,杨晓君,梅玉萍.2006.湖南骑田岭花岗岩及其暗色微粒包体的地球化学与壳幔岩浆的混合作用.地球学报,27(6):557-569.
侯光久,索书田,郑贵州,魏启荣.1998.雪峰山加里东造山运动及其体制转换.湖南地质,17(3):141-144.
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黄标,孙明志,武少兴,刘刚.1994.武夷山中段加里东期混合岩的特征及成因讨论.岩石学报,10(4):427-439.
李文杰,梁金城,冯佐海,张桂林,陈懋弘,袁爱平.2006.桂东北地区几个加里东期花岗岩体的地球化学特征及其构造环境判别.矿产与地质,20(4-5):353-360.
李献华,桂训唐.1991.万洋山-诸广山加里东期花岗岩的物质来源——Sr-Nd-Pb-O多元同位素体系示踪.中国科学(B辑),5:533-540.
李献华.1993.万洋山-诸广山加里东期花岗岩的形成机制——微量元素和稀土元素地球化学证据.地球化学,1:218-228.
李耀松,朱杰晨,郑懋公,吴莹莹,胡振择.1986.九嶷山花岗杂岩体的Rb-Sr年代学及其成因.铀矿地质,2(5):257-264.
李宗怀,韩宝福,李辛子,杜蔚,杨斌.2004.新疆准噶尔地区花岗岩中微粒闪长质包体特征及后碰撞花岗质岩浆起源和演化.岩石矿物学杂志,23(3):214-226.
楼法生,舒良树,于津海,王德滋.2002.江西武功山穹隆花岗岩岩石地球化学特征与成因.地质论评,48(1):80-88.
路远发.2004.GeoKit:一个用VBA构建的地球化学工具软件包.地球化学,33(5):459-464.
毛建仁,陶奎元,邢光福,杨祝良,赵宇.1999.中国东南大陆边缘中新生代地幔柱活动的岩石学纪录.地球学报,20(3):253-258.
毛景文,李红艳,王登红.1998.华南地区中生代多金属矿床形成与地幔柱活动的岩石学纪录.矿物岩石地球化学通报,19(2):130-132.
莫柱孙,叶伯丹,潘维祖.1980.南岭花岗岩地质学.北京:地质出版社.
南京大学地质学系.1981.华南不同时代花岗岩类及其与成矿关系.北京:科学出版社.
赖绍聪,隆平.1997.江西茅排金矿床含金韧性剪切带构造特征.西北地质,18(3):53-58.
彭松柏,金振民,付建明,刘云华,何龙清,蔡明海.2006.两广云开隆起区基性侵入岩的地球化学特征及其构造意义.地质通报,25(4):434-441.
丘元禧,马文璞,范小林,张渝昌,邓家瑞,夏亮辉,张旭亮.1996.“雪峰古陆”加里东期的构造性质和构造演化.中国区域地质,2:150-160.
沙连堃,袁奎荣.1991.广西大宁花岗闪长岩中暗色微粒包体的地球化学及成因模式.地球科学,16(4):377-386.
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