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引用本文:伍光英1, 2 马铁球3 冯艳芳2 闫全人1 刘富国3 柏道远3. 南岭万洋山加里东期花岗岩地质地球化学特征及其成因[J]. 中国地质, 2008, 35(4): 608-617.
WU Guang-ying1,2, MA Tie-qiu3, FENG Yan-fang2, YAN Quanren1, LIU Fu-guo3, BO Dao-yuan3. Geological and geochemical characteristics and genesis of the Caledonian Wanyangshan granite in the Nanling Mountains, South China[J]. Geology in China, 2008, 35(4): 608-617(in Chinese with English abstract).
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南岭万洋山加里东期花岗岩地质地球化学特征及其成因
伍光英1, 2 马铁球3 冯艳芳2 闫全人1 刘富国3 柏道远31,2,3
1.中国地质科学院地质研究所,北京 100037;2.中国地质调查局发展研究中心,北京 100037;3.湖南省地质调查院, 湖南 湘潭 411100
摘要:
提要:通过岩体地质地球化学等特征的调查研究,对万洋山花岗岩体进行了岩石谱系单位划分,认为它是加里东期多阶段岩浆活动形成的复式岩体。花岗岩岩石类型主要为黑云母花岗闪长岩、黑云母二长花岗岩、二云母二长花岗岩,其中,黑云母花岗闪长岩、黑云母二长花岗岩中含有较多的暗色镁铁质微粒包体。SiO2含量为66.99%~73.04%,K2O平均含量为3.91%,Na2O+K2O为6.26%~7.39%,K2O/Na2O平均值为1.45,Al2O3平均值为13.74%;Ba、Nb、Sr、P、Ti亏损较明显,Rb、(Th+U)、(La+Ce)、Nd、(Zr+Hf+Sm)、(Y+Yb)等则相对富集;ΣREE平均为264.43×10-6,重稀土富集;ΣCe/ΣY平均比值为1.8;(La/Yb)N比值平均7.13;Eu弱亏损,δEu值平均为0.53;ISr值为0.71223~0.71376,εSr(t)值为109.8~131.5,εNd (t)值为-7.1~-8.3,t2DM为1.74~1.86 Ga;研究表明万洋山花岗岩属铁质、(强)过铝高钾钙碱性S型花岗岩,形成于后造山构造环境;岩浆源区的物质是多源的,主要是含有深源岩浆固结产物的地壳物质;或是加里东期间扬子地块和华夏地块间发生碰撞前的侵入有深源岩浆岩或岛弧型岩浆岩的地壳物质;早期次单元花岗岩的岩浆源可能还有幔源岩浆混染或局部混合。
关键词:  地球化学特征  物质来源  构造环境  花岗岩  万洋山  南岭
DOI:
分类号:
基金项目:中国地质调查局地质大调查项目(1212010813043、200213000035、1212010633803)资助。
Geological and geochemical characteristics and genesis of the Caledonian Wanyangshan granite in the Nanling Mountains, South China
WU Guang-ying1,2, MA Tie-qiu3, FENG Yan-fang2, YAN Quanren1, LIU Fu-guo3, BO Dao-yuan31,2,3
1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Research and Development Center, China Geological Survey, Beijing 100083, China;3. Hunan Institute of Regional Geological Survey, Xiangtan 411100, Hunan, China
Abstract:
Abstract:Field observations suggest that the Wanyangshan granite batholith is a complex batholith composed of different intrusive units that were sourced from multiple magmatism during the Caledonian. The types of granite in the batholith include biotite granodiorite, biotite monzogranite, and biotite-muscovite monzogranite. There are many very fine-grained mafic xenoliths in biotite granodiorite and biotite monzogranite. U-Pb analyses of zircons show that the Wanyangshan granite batholith formed in the Silurian, at ca 441-462 Ma. Geochemical analyses showed that:the Wanyangshan granite has a SiO2 content of 66.99 to 73.04%, an average K2O content of 3.91% and an average Al2O3 content of 13.74%, with Na2O+K2O=6.26 to 7.39% and K2O/Na2O=1.45 on the average. The Wanyangshan granite has a higher total REE concentration (264.43 g/g). Chondrite-normalized REE patterns show a significant differentiation between LREE and HREE and a remarkable enrichment in LREE. Eu values (Eu=0.53) indicate that the primitive magma was basic and enriched in plagioclase most likely. The Wanyangshan granite is significantly depleted in HFSE (Ta, Nb, Sr, P, and Ti), which indicates that these granite samples are strongly related with subduction. For isotopic compositions, the Wanyangshan granite has a range of initial strontium from 0.71223 to 0.71376, and a range of epsilon strontium (εSr(t)) from 109.8 to 131.5. Epsilon neodymium (εNd(t)) ranges from -7.1 to -8.3, with the depleted mantle model age of 1.74-1.86 Ga. In general, geochemical and isotopic analyses indicate that the Wanyangshan granite is ferruginous, peraluminous, high-K, calc-alkaline S-type granite, with higher concentrations of aluminium and potassium. Its primitive magma could be mainly sourced from melting of the crust, and is most likely to have been contaminated by the mantle in the early stage of magmatism evolution. The Wanyangshan granite formed under the conditions of post-orogenic extension after the collision between the Cathaysian and Yangtze blocks in the Caledonian.
Key words:  geochemistry  material source  tectonic setting  granite  Wanyangshan  Nanling