| 大别造山带前陆阳新盆地古近纪玄武岩地球化学特征与成因研究 |
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| 引用本文：薛怀民,董树文,刘晓春,李三忠.2004.大别造山带前陆阳新盆地古近纪玄武岩地球化学特征与成因研究[J].地球学报,25(1):25-32. |
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| 基金项目:国家“973”项目(TG1999075505)和(2003CB716502)，地质调查项目“湖北红安地区构造和年代格架与高压-超高压变质带的演化”(200013000169) |
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| 中文摘要:大别造山带前陆阳新盆地古近纪玄武岩的成分从石英拉斑玄武质到橄榄拉斑玄武质，以相对较高的大离子亲石元素(Rb、Ba、K、Th、U等)丰度和弱到中等亏损高场强元素(Nb和Ta)为特征，岩石地球化学的总体特征类似于初始裂谷的拉斑玄武岩，而与大陆拉斑玄武岩所表现出的强烈亏损高场强元素Nb和Ta的地球化学特征明显不同。该拉斑玄武质岩浆喷发前曾经历过较小程度(约4．5％)的以橄榄石为主的矿物分离结晶，玄武岩的母岩浆则是源区物质经过约15％的部分熔融形成的，源区物质可能包含了来自下地幔的FOZO和富集型大陆岩石圈地幔两种组分。大别造山带内及前、后陆地区古近纪拉斑玄武岩的地球化学特征具有可比性，意味着随着大别造山带山根的拆沉，来自下地幔的FOZO岩浆(可能以地幔柱的形式)上涌，对大陆岩石圈的地幔部分发生了大规模的改造，使得原性质明显不同的两大岩石圈地幔在会聚带附近其地球化学分区性变得模糊。所形成的玄武岩总体具有较多的FOZO特征，但(除造山带内部)也不同程度地保留有岩石圈地幔的性质。 |
| 中文关键词:古近纪玄武岩 岩石圈地幔 下地幔 阳新盆地 |
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| Geochemistry and Genesis of Paleogene Bsalts in the Yangxin Basin,Foreland of the Dabie Orogen |
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| Abstract:The Paleogene basalts in the Yangxin basin on the foreland of the Dabie orogen are from quartz tholeiitic basalt to olivine-tholeiitic basalt in composition, characterized by relative richness of large ion lithophile (LIL) elements (Rb, Ba,K,Th,U),and slight to medium degree depletion of high field strength (HFS) elements (Nb,Ta).The rocks are generally similar to the initial rifting tholeiitic basalt in geochemical features but distinctly different from continental tholeiitic basalt, which is characterized by strong depletion of HFS (Nb, Ta) elements. The tholeiitic basaltic magma had undergone fractional crystallization of minerals (mainly olivine) by about 4.5 percent before extrusion,and the primary magma was formed by about 15 percent partial melting of source materials, which might have included two components, i.e., the FOZO from the lower mantle and the enriched continental lithospheric mantle. Geochemical characteristics of the Eogene tholeiitic basalts in different parts of the orogen have affinity. This suggests that, with the delamination of the mountain root, the FOZO magma from the lower mantle (probably as mantle plume) migrated upward and reformed the continental lithospheric mantle extensively, causing the indistinctness of two large blocks of lithospheric mantle (Yangtze and North China) near the subduction zone. Except for those within the orogen, the basalts formed have more FOZO characteristics but preserve different degrees of lithospheric mantle features. |
| keywords:Paleogene basalt lithospheric mantle lower mantle Yangxin basin |
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