滇中甸中地区中二叠世晚期镁铁—超镁铁质岩体特征及其与峨眉地幔柱关系——来自锆石U-Pb年龄及岩石地球化学证据
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本文为云南省1∶5万撒马基幅、因民幅、贵城幅、舒姑幅区域地质调查(编号:D201905)、云南1∶5万二街、易门、鸣矣河、上浦贝幅区域地质调查(编号:DD20160017)、云南区域地质调查片区总结与服务产品开发(编号:121201102000150012- 02)的成果


Characteristics of the late Middle Permian mafic—ultramafic rocks in Dianzhong area,central Yunnan, and their relationship with the Emei Mantle Plume——Evidence from zircon U-Pb age and petrogeochemistry
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    摘要:

    通过1∶5万区域地质调查,在峨山县甸中地区新发现了镁铁—超镁铁质碱性岩体,其岩性为含石榴磷灰辉石岩及正长辉长岩。岩石地球化学表明,该岩体SiO2含量为(42. 74% ~ 45. 11%),普遍具有高MgO(8. 78% ~ 11. 13%)、富铁(全铁含量)、低TiO2(0. 88% ~ 2. 45%),低Na2O(0. 17% ~ 0. 62%)、富碱的特征;富集Rb、Ba、Sr、Th等大离子亲石元素(LILE),相对亏损Nb、Zr、Ti、Hf等高场强元素(HFSE)及重稀土元素Yb、Y;岩浆形成过程中具中等的部分熔融程度(约10% ~ 15%),且后期经历了明显的结晶分异作用。对辉石岩及辉长岩进行锆石U- Pb LA- ICP- MS定年,年龄分别为260. 2 ± 1. 6 Ma(MSWD = 0. 4,n= 10)和264. 0 ± 1. 3 Ma(MSWD = 2. 4,n = 23),属中二叠世晚期,与峨眉山玄武岩具有相似的地球化学特征及侵位年龄。结合区域资料及上述特征,本文认为,峨山县甸中地区镁铁—超镁铁质碱性岩体应属于峨眉山地幔柱活动产物,是峨眉山玄武岩的侵入相,代表了峨眉山玄武岩的一个分枝柱头;本次的发现,对丰富峨眉山大火成岩省资料具有重要的意义。

    Abstract:

    Objectives: After a regional geological survey of 1∶50 000, new mafic—ultramafic alkaline rock bodies were newly discovered in the Dianzhong area of Eshan County. The lithology is garnet- containing apatite rock and syenite. Petrogeochemistry shows that the SiO2content of the rock is 42.74% ~ 45.11%, which generally has high MgO (8.78% ~ 11.13%), iron- rich (full iron content), low TiO2(0.88% ~ 2.45%), and low Na2O (0.17% ~ 0.62%), alkali- rich characteristics. Results:Enrichment of large ion lithophilic elements (LILE) such as Rb, Ba, Sr, and Th, relative loss of high field strength elements (HFSE) such as Nb, Zr, Ti, Hf and heavy rare earth elements Yb, Y, during the magma formation process, it had a moderate degree of partial melting (about 10% to 15%), and experienced significant crystal differentiation in the later stage. Zircon U- Pb LA- ICP- MS dating of pyroxene and gabbro, 260.2 ± 1.6 Ma (MSWD = 0.4, n = 10) and 264.0 ± 1.3 Ma (MSWD = 2.4, n= 23).Conclusions:Belongs to the late Middle Permian, and has similar geochemical characteristics and emplacement age to the Emeishan basalt. Based on the regional data and the above characteristics, this paper believes that the mafic—ultramafic alkaline rock in the Dianzhong area of Eshan County belongs to the product of the Emeishan mantle plume. This discovery is of great significance for enriching the data of the Emeishan large igneous province.

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刘军平,王晓峰,王小虎,杨爱平,宋冬虎,田素梅,夏彩香,张坤,杨仕潘.2020.滇中甸中地区中二叠世晚期镁铁—超镁铁质岩体特征及其与峨眉地幔柱关系——来自锆石U-Pb年龄及岩石地球化学证据[J].地质论评,66(5):1284-1298,[DOI].
LIU Junping, WANG Xiaofeng, WANG Xiaohu, YANG Aiping, SONG Donghu, TIAN Sumei, XIA Caixiang, ZHANG Kun, YANG Shipan.2020. Characteristics of the late Middle Permian mafic—ultramafic rocks in Dianzhong area,central Yunnan, and their relationship with the Emei Mantle Plume——Evidence from zircon U-Pb age and petrogeochemistry[J]. Geological Review,66(5):1284-1298.

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  • 收稿日期:2019-12-31
  • 最后修改日期:2020-06-24
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  • 在线发布日期: 2020-09-19
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