北京大学学报自然科学版 ›› 2020, Vol. 56 ›› Issue (3): 436-448.DOI: 10.13209/j.0479-8023.2020.028

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西秦岭中生代花岗岩锆石U-Pb-Lu-Hf同位素特征及地质意义

刘巍1, 郭丽爽2, 廖延福3, 赵永红1, 刘玉琳1,4,†, 肖彦君1   

  1. 1. 北京大学地球与空间科学学院, 北京 100871 2. 中国地震局地壳应力研究所地壳动力学重点实验室, 北京 100085 3. 陕西天地矿业有限公司, 西安 710068 4. 造山带与地壳演化教育部重点实验室, 北京 100871
  • 收稿日期:2019-02-03 修回日期:2020-03-31 出版日期:2020-05-20 发布日期:2020-05-20
  • 通讯作者: 刘玉琳, E-mail: ylliu(at)pku.edu.cn
  • 基金资助:
    中国地质调查局地质调查项目(12120114050301)资助

Zircon U-Pb-Lu-Hf Isotopic Characteristics and Geological Implications of Mesozoic Granites in Western Qinling

LIU Wei1, GUO Lishuang2, LIAO Yanfu3, ZHAO Yonghong1, LIU Yulin1,4,†, XIAO Yanjun1   

  1. 1. School of Earth and Space Sciences, Peking University, Beijing 100871 2. Key Laboratory of Crustal Dynamics, China Earthquake Administration, Beijing 100085 3. Shaanxi Tiandi Geology Co. Ltd, Xi’an 710068 4. Key Laboratory of Orogenic Belts and Crustal Evolution (MOE), Beijing 100871
  • Received:2019-02-03 Revised:2020-03-31 Online:2020-05-20 Published:2020-05-20
  • Contact: LIU Yulin, E-mail: ylliu(at)pku.edu.cn

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摘要：

对西秦岭地区中川岩体、柏家庄岩体和教场坝花岗岩体进行LA-ICP-MS锆石U-Pb同位素年代学分析, 获得其岩浆侵位年龄分别为220±1, 216±6和222±3 Ma, 表明3个岩体均形成于中?晚三叠世。样品的全岩地球化学分析结果表明, 3个岩体具有相似的稀土及微量元素特征, 均表现为显著亏损高场强元素Nb, Ti和P等, 具有明显的右倾式球粒陨石标准化稀土元素配分模式。锆石Lu-Hf同位素分析结果表明, 3个岩体锆石测年样品的εHf(t)值介于?3.31~+1.68之间, 二阶段模式年龄介于1151~1456 Ma之间。岩石成因分析表明, 这些印支期花岗岩体的母岩浆主要来源于新元古代地壳物质的部分熔融。结合岩体形成时代、岩石成因和区域岩浆作用, 认为这些岩体形成于南秦岭与华南板块沿勉略缝合带相碰撞的造山动力学背景, 可能与华南板块的俯冲板片断离有关。

关键词: 西秦岭, 花岗岩体, 锆石U-Pb-Lu-Hf 同位素, 全岩地球化学, 岩石成因

Abstract:

LA-ICP-MS zircon U-Pb isotopic analyses reveal that the granitoid intrusions of Zhongchuan, Baijiazhuang and Jiaochangba in Western Qinling orogeny emplaced at ages of 220±1, 216±6 and 222±6 Ma, respectively, showing that all of them belongs to Middle-Late Triassic granitoid magmatism. Whole rock geochemistry analyses indicate that the primitive mantle-normalized trace element patterns and Chondrite-normalized REE patterns of the rock samples from the three intrusions show significant similarity, for example, depletion in high field strength elements of Nb, Ti and P, and enrichment in LREE. Analyses for zircon Lu-Hf isotopes indicate that the εHf(t) values range from ?3.31 to +1.68 of the three intrusions with the two-stage model ages between 1151 and 1456 Ma. Petrogenetic studies indicate that the granitoid magmas of these Indosinian granitoid intrusions were derived mainly from the partial melting of mesoproterozoic crust material. Combined with the formation age, petrogenesis and tectonic background, these Indosinian intrusions were most likely formed in the collision process between South Qinling orogen and South China Block along Mianlue suture zone, and might be related to the subducted slab break off of South China Block.

Key words: Western Qinling, granitoid intrusions, zircon U-Pb-Lu-Hf isotopes, whole rock geochemistry, petrogenesis

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