| 南秦岭小茅岭复式岩体地球化学特征及其构造意义 |
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| 关键词:Xiaomaoling composite intrusives petro-geochemistry Sr-Nd-Hf isotope Qinling orogenic belt |
| 基金项目:中国地质调查局地质调查工作项目(编号: DD20160343-01);中央公益性科研院所基本科研业务费(编号: J1605) |
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| Geochemical Characteristics and Tectonic Implications of the Xiaomaoling Composite Intrusives in South Qinling Orogenic Belt |
| The Xiaomaoling composite intrusives, exposed in the northernmost part of South Qinling, are composed of Songjiawuchang diabase (grabbro) and Mihunzhen, Mogouxia and Yejiawan diorites with the age of 870~840 Ma. The geochemical analysis shows that the Songjiawuchang basic intrusion belongs to sub-alkaline series and is rich in LREE and LILE, slightly negative in Nb, Ta, Ti and P elements and has high content of Zr and Hf elements, high ratios of Zr/Y and Ta/Yb but low ratios of Zr/Nb. All the above characteristics are similar to those of typical Island Arc Basalts; in the tectonic discrimination diagrams, the Songjiawuchang samples fall in the VAB area. The enrichment of some elements might have resulted from lithospheric mantle metasomatized by the fluid of the subducted block. The Mihunzhen, Mogouxia and Yejiawan diorites belong to quasi aluminum sub-alkaline series and have the geochemical features of island arc magmatic rocks. Based on Sr-Nd-Hf isotopic analysis, the authors hold that Songjiawuchang intrusion was mainly derived from depleted mantle. The Mogouxia and Yejiawan diorites were derived from newly-created basic lower crust while the Mihunzhen diorite may be the product of ancient crust melting. All the geochemical data show that the Xiaomaoling composite intrusives were formed in an island-arc tectonic setting in 870~840 Ma. The metasomatized mantle wedge was partially melted and the produced magma was emplaced to form the Songjiawuchang intrusion. As a result of the basic magma heating, the overlying newly-created basic lower crust and ancient crust began melting and formed the Mogouxia, Yejiawan and Mihunzhen intrusions. Combined with the available ~850–780 Ma metamorphism and magmatism in the Douling area, the authors hold that there probably existed a period of early Neoproterozoic tectonic-magmatic-metamorphic events in the Xiaomaoling–Douling uplift of the South Qinling orogenic belt. The regional tectonic attributes of these events deserve further studies. |
| LIU Ren-yan,LI Qing-shan,NIU Bao-gui,HE Zheng-jun,REN Ji-shun.2018.Geochemical Characteristics and Tectonic Implications of the Xiaomaoling Composite Intrusives in South Qinling Orogenic Belt[J].Acta Geoscientica Sinica,39(2):201-215. |
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