| 拉萨地体南缘早始新世荣玛辉长岩年代学、岩石地球化学特征及其地质意义 |
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| 引用本文： | 董咪,郎兴海,邓煜霖,王旭辉.拉萨地体南缘早始新世荣玛辉长岩年代学、岩石地球化学特征及其地质意义[J].地球科学,2022,47(4):1349-1370. |
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| 作者姓名： | 董咪 郎兴海 邓煜霖 王旭辉 |
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| 作者单位： | 成都理工大学地球科学学院，四川成都 610059 |
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| 基金项目： | 四川省科技计划项目(No.2020JDJQ0042)；;国家自然科学基金项目(Nos.41502079,41972084)；;国家重点研发计划课题(No.2018YFC0604105)；;西北大学大陆动力学国家重点实验室开放基金(No.18LCD04)；;中国地质调查局项目(Nos.DD20190167,DD20160346)； |
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| 摘 要： | 印度-欧亚大陆初始碰撞后的新特提斯洋板片断离过程至今尚未得到较好的约束.对拉萨地体南缘荣玛地区早始新世辉长岩开展了锆石U-Pb定年、全岩主微量及Sr-Nd同位素分析，探讨了岩石成因及动力学意义，以进一步约束新特提斯洋板片断离过程.研究结果表明，荣玛辉长岩的锆石U-Pb年龄为51±1 Ma，形成于早始新世；地球化学特征显示富集大离子亲石元素（Rb、Sr、Ba），亏损高场强元素（Nb、Ta、Ti），初始87Sr/86Sr比值为0.705 9~0.706 6，εNd（t）值为+3.1~+3.3；与典型弧岩浆岩相比具有较高的Zr（134.28×10-6~230.07×10-6）、TiO2（1.04%~1.51%）、Nb（9.01×10-6~14.67×10-6）含量，显示出典型板内玄武岩的地球化学属性.岩石源区除了来自俯冲板片释放的流体交代的岩石圈亏损地幔外，同时可能受到深部软流圈地幔物质的加入.结合南部拉萨地体已发表的始新世岩浆岩的地球化学及年代学数据，进一步约束新特提斯洋板片断离时间不晚于51 Ma.
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| 关 键 词： | 早始新世 南部拉萨地体 辉长岩 板片断离 新特提斯洋 地球化学 |
| 收稿时间： | 2021-06-20 |
Geochronology and Geochemistry Implications for Early Eocene Rongma Gabbros in Southern Margin of Lhasa Terrane,Tibet |
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| Dong Mi,Lang Xinghai,Deng Yulin,Wang Xuhui.Geochronology and Geochemistry Implications for Early Eocene Rongma Gabbros in Southern Margin of Lhasa Terrane,Tibet[J].Earth Science-Journal of China University of Geosciences,2022,47(4):1349-1370. |
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| Authors: | Dong Mi Lang Xinghai Deng Yulin Wang Xuhui |
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| Abstract: | The slab breakoff of the Neo-Tethys Ocean after the initial India-Asia collisional has not been well constrained up to now. In this paper, zircon U-Pb dating, whole rock major and trace element and Sr-Nd isotopes analysis of the Early Eocene gabbros in the Rongma area on the southern margin of the Lhasa terrane have been carried out, the petrogenesis and geodynamical implication are discussed to further constrain the slab breakoff of the Neo-Tethyan oceanic slab.The results show that zircon U-Pb ages of 51±1 Ma have been obtained for Rongma gabbros, indicating they were formed in the Early Eocene.The Rongma gabbros are enriched in LILEs (such as Rb, Sr, Ba) and depleted in HFSEs (such as Nb, Ta, Ti) with initial 87Sr/86Sr=0.705 9-0.706 6 and εNd(t)=+3.1-+3.3. Compared with typical arc magmas, the Rongma gabbros have high contents of Zr (134.28×10-6-230.07×10-6), TiO2(1.04%-1.51%) and Nb (9.01×10-6-14.67×10-6), suggesting a geochemical intraplate-affinity. In addition, Rongma gabbros were derived from depleted lithospheric mantle which metasomatized by slab-derived fluids during Neo-Tethyan subduction, accompanied with significant contributions from deep asthenosphere mantle.Combined with the geochemical and geochronological data of the Cenozoic magmatic rocks from the southern Lhasa terrane, it further proposes that slab breakoff of the Neo-Tethys Ocean has occurred before 51 Ma. |
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