扬子板块西缘黄草坝A型复式花岗岩体的成因及其地质意义
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本文为国家自然科学基金资助项目(编号:42072096)、中国核工业地质局重点科研项目(编号:2023- 16)和成都理工大学珠峰科技计划(编号:2023ZF11413)的成果


Genesis and geological significance of Huangcaoba A- type composite granite pluton, western margin of Yangtze Block
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    摘要:

    扬子板块西缘分布有一系列中元古代晚期—新元古代中期的岩浆岩体,是探究Rodinia超大陆聚合和裂解的重要窗口。黄草坝复式花岗岩体出露于扬子西南缘的云南牟定戌街地区,岩性包括有片麻状花岗岩、二长花岗岩和黑云母花岗岩。这些花岗岩在主量元素组成上均具有高SiO2(70. 77% ~ 78. 79%)、高碱(Na2O + K2O = 7. 15% ~ 8. 73%)、高FeOT/(FeOT + MgO)(0. 70 ~ 0. 98)值和高10000 × Ga/Al(2. 68 ~ 6. 84)值,以及低P2O5(0. 01% ~ 0. 06%)、低CaO(0. 07% ~ 0. 90%)、低MgO(0. 02% ~ 0. 88%)的地球化学特点。在稀土元素组成上均表现为轻稀土相对富集、具明显的负Eu异常特征。在微量元素组成上表现为Rb、Th、U、K、Nd、Sm等元素相对富集,Nb、Zr、Hf等元素相对亏损,Ba、Sr、P、Ti等元素强烈亏损。主微量元素特征表明黄草坝复式花岗岩体属于典型的A型花岗岩。锆石原位微区U- Pb定年结果显示片麻状花岗岩(1090 ± 24 Ma)和二长花岗岩(1063 ± 5 Ma)均形成于中元古代时期,εHf(t) = + 4. 3 ~ + 10. 3,TDM2年龄介于1. 33 ~ 1. 62 Ga,表明成岩物质来自新生地壳的部分熔融。黑云母花岗岩的结晶年龄为782. 4 ± 8. 2 Ma(ICP- MS U- Pb法),属于新元古代,其εHf(t) = -7. 3 ~ -2. 1,TDM2年龄介于1. 80 ~ 2. 14 Ga,表明成岩物质可能来源于古老地壳。结合前人研究资料分析,本文认为黄草坝A型复式花岗岩体形成于中元古代—新元古代时期多阶段造山旋回中的碰撞造山后伸展环境中。

    Abstract:

    A series of granitoids are distributed in the western margin of the Yangtze Block from late Mesoproterozoic to middle Neoproterozoic, which is an important window to explore the convergence and disintegration of the Rodinia supercontinent. The Huangcaoba granitoid pluton, which consists of gneissic granite, monzonitic granite and biotite granite, is located in Xujie area of Mouding County, Yunnan Province of the western margin of the Yangtze Block. The granites have the characteristics of high silicon (SiO2 70.77% ~ 78.79%), high alkali (Na2O + K2O) (7.15% ~ 8.73%), high ratio of FeOT/ (FeOT + MgO) (0.70 ~ 0.98) and 10000 × Ga/Al (2.68 ~ 6.84), low calcium (CaO 0.07% ~ 0.90%), and low magnesium (MgO 0.02% ~ 0.88%) in terms of main element composition. In terms of REE composition, the LREE is relatively enriched and has obvious negative Eu anomaly characteristics. In terms of trace elements, Rb, Th, U, K, Nd, and Sm are relatively enriched, Nb, Zr, Hf are relatively depleted, and Ba, Sr, P, Ti are strongly depleted. The characteristics of main element and trace elements indicate that the Huangcaoba A- type granitoid pluton belong to A- type granite. In situ U- Pb dating of zircon shows that the gneissic granite (1090 ± 24 Ma) and monzonite granite (1063 ± 5 Ma) were both formed in the Middle Proterozoic era, εHf(t) = +4.3 ~ +10.3, TDM2 age is 1.33 ~ 1.62Ga, indicating that the diagenetic material comes from the partial melting of the new crust. The crystallization age of biotite granites is 782.4 ± 8.2 Ma (ICP- MA U- Pb method), belonging to the Neoproterozoic era, with εHf(t)= -7.3 ~ -2.1, which all fall below the chondrite evolution line. The TDM2 age is between 1.80 ~ 2.14 Ga, indicating that the ore- forming materials are more likely to come from the ancient crust. Based on the analysis of previous research data, the paper holds that the Huangcaoba A- type granitoid pluton was originated in post orogenic extension environment during the multi- stage orogenic cycle in the Mesoproterozoic to Neoproterozoic period.

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黄露玉,陈友良,郭锐,殷桂芹,范伟,詹国鑫,郭俏萍.2024.扬子板块西缘黄草坝A型复式花岗岩体的成因及其地质意义[J].地质论评,70(3):2024030021,[DOI].
HUANG Luyu, CHEN Youliang, GUO Rui, YIN Guiqin, FAN Wei, ZHAN Guoxin, GUO Qiaoping.2024. Genesis and geological significance of Huangcaoba A- type composite granite pluton, western margin of Yangtze Block[J]. Geological Review,70(3):2024030021.

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  • 收稿日期:2024-01-11
  • 最后修改日期:2024-05-17
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  • 在线发布日期: 2024-06-20
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