| 江西会昌岽背玄武岩地球化学和Sr-Nd同位素特征及其地质意义 |
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| 引用本文：毛建仁,骆学全,徐贻赣,汪惠惠.2009.Geochemical and Sr-Nd isotopic characteristics of Dongbei basalts in Huichang area, Jiangxi Province, and their geological implications [J].Mineral Deposits,28(5):696~706 |
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| 基金项目:江西瑞金-会昌地区矿产远景地质调查（项目编号：矿调［2005］13-6）和中国地 质调查局科技外事部基础研究项目（1212010611805） |
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| 中文摘要:江西会昌岽背地区晚中生代玄武岩的SiO2含量为49.06 %～50.14 %，K2O含量为1.26 %～1.63 %。其微量元素显示出大离子亲石元素富集，高场强元素亏损，尤以明显的Nb、Ta亏损为特征；REE总量为 (135.5～146.8)×10-6，(La/Yb)N≈10，表现出LREE富集的稀土元素配分模式，且无明显的Eu异常；Sr-Nd同位素具有高(87Sr/86Sr)i（0.70678～0.70695）和低εNd(t)（-2.46～-2.18）的特征。据以上特征并结合区域地质背景，反映出岽背玄武岩的源区可能为EMⅡ型富集型大陆岩石圈地幔，其形成的构造环境为活动大陆边缘。较低的Nb/U比值（7～8）暗示该玄武质岩浆在形成过程中遭受了一定程度的大陆地壳混染或与俯冲过程有关的物质的加入。岽背玄武岩具有陆缘弧型地球化学特征，指示会昌地区在晚白垩世晚期（约85 Ma）处于活动大陆边缘的构造环境，该玄武岩的形成可能与燕山晚期古太平洋板块向欧亚大陆的俯冲消减作用关系密切。底侵作用可能为会昌地区燕山晚期成矿岩浆的生成提供了流体和热，有利于铜多金属矿的形成。 |
| 中文关键词:地球化学 Sr-Nd同位素 玄武岩 EMⅡ型地幔源区 活动大陆边缘 会昌 江西 |
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| Geochemical and Sr-Nd isotopic characteristics of Dongbei basalts in Huichang area, Jiangxi Province, and their geological implications |
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| Abstract:The Late Mesozoic Dongbei basalts, located in Huichang area of Jiangxi Province, have SiO2 contents of 49.06%～50.14% and K2O 1.26%～1.63%. They are rich in l arge-ion lithosphile elements and poor in high field strength elements, and have ∑REE of (135.5～146.8)×10-6,(La/Yb)N of ca.10 and LREE enrichment, with strong negative Nb and Ta anomalies and no obvious Eu anomalies in the MORB-normalized sp ider diagram. The Sr-Nd isotopic compositions show that Dongbei basalts have hig h initial 87Sr/86Sr ratios of 0.70678～0.70695 and low εNd(t) of -2.46～-2.18. These geochemical characteristics indicate that the Dongbei basalts might have been derived from the source of EMⅡ-type lithospheric mantle under the tectonic setting of an active continental margin. The low value s of Nb/U (7～8) suggest that the basalts probably experienced the addition of s ome subduction-related materials and/or a certain degree of crust contamination. The characteristics of the Dongbei basalts are similar to those of the basalts with the tectonic settings of an active continent margin, indicating that Huicha ng area lays in an active epicontinental environment during the late stage of La te Cretaceous (ca. 85 Ma). The Dongbei basalts might have had an intimate contact with the paleo-Pacific plate subduction underneath the Eurasia plate in the lat e Yanshanian period. The basaltic underplating may have provided fluid component s and heat for the metallogenic magma of Huichang area during the late Yanshania n period, which contributed to the formation of copper deposits. |
| keywords:geochemistry, Sr-Nd isotopic component, basalt, EMⅡ mantle source, active continental margin, Huichang, Jiangxi |
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