班韦乌卢地块中部变质表壳岩碎屑锆石U- Pb年代学、Hf同位素研究及其构造意义
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本文为商务部援外项目(编号〖JP2〗\[2015\]352和\[2012\]558)及中国地质调查局项目(编号DD20201150和1212011220910)〖JP〗共同资助的结果。


Study of U- Pb chronology and Hf isotopes of detrital zircons from metamorphic supracrustal rocks in the central part of the Bangweulu block and its tectonic significance
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    摘要:

    通过LA- MC- ICP- MS 碎屑锆石微区U- Pb 定年和Hf 同位素分析,对班韦乌卢地块中部地区基底变质表壳岩进行了同位素定年及物源示踪研究。结果显示,两件样品的碎屑锆石峰值年龄分布表现出较好的一致性,总体呈现出2490~2059 Ma、2044~1954 Ma、1942~1887 Ma、1865~1817 Ma以及1641~1522 Ma五个年龄组,分别与班韦乌卢地块内的构造岩浆事件相吻合。综合区域地质特征与碎屑锆石年龄谱特征分析认为:原岩蚀源区比较复杂,近源区古元古代花岗岩、花岗片麻岩及火山岩是主要的蚀源区。根据碎屑锆石最小年龄1522±23 Ma,推测表壳岩原岩形成时代上限可能为中元古代,而不是之前认为的形成于古元古代。碎屑锆石的 ε Hf( t )值介于-6. 26~7. 37之间(平均1. 37),由负到正变化范围较大,表明它们除来自古老地壳的再循环物质外,还存在新生地壳的物质来源。 t DM 2峰值年龄出现在2. 40~2. 50 Ga,说明班韦乌卢地块地壳增生事件主要发生于古元古代,可能与凯诺兰超大陆的聚合过程有关,其晚于全球大陆地壳主增长期,说明了地壳增生的长期性和在地质历史时期增长速度的不稳定性。

    Abstract:

    The LA- MC- ICP- MS detrital zircon microzone U- Pb dating and Hf isotope analysis were used for isotope dating and provenance tracing of the basement metamorphic supracrustal rock in the central area of the Bangweulu block. The results show that the detrital zircon peak age distributions of the two samples show high consistency, withfive age groups of 2490~2059 Ma, 2044~1954 Ma, 1942~1887 Ma, 1865~1817 Ma and 1641~1522 Ma, respectively, which are consistent with tectonic and magmatic events in the Bangweulu block, respectively. Based on the analysis of regional geologicaland detrital zircon age spectrum characteristics, it is concluded that the provenance is relatively complex, and the proximal provenance consists mainly of paleoproterozoic granite, granite gneisses and volcanic rocks. Based on the minimum age of detrital zircon (1522±23 Ma), the upper limit of the sedimentary age of clastic rocks issuggested to be Mesoproterozoic rather than Paleoproterozoic. The ε Hf( t ) values of detrital zircons range from -6. 26 to 7. 37 (average 1. 37), with a wide range from negative to positive, indicating that they are not only originated fromtherecycled materials from the ancient crust, but also include materials from the newly accreted crust. The peak age of tDM2 appeared at 2. 40~2. 50 Ga, indicating that the crustal accretion event of the Bangweulu block mainly occurred in the Paleoproterozoic, which may be related to the aggregation process of the Kenorland supercontinent. It is later than the main growth period of the global continental crust, indicating the long- term nature of crustal accretion and the instability of its growth rate during geological history.

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孙宏伟,王杰,任军平,古阿雷,左立波,刘子江,邢仕,苏晓云,Alphet Phaskani DOKOWE, Ezekiah CHIKAMBWE.2021.班韦乌卢地块中部变质表壳岩碎屑锆石U- Pb年代学、Hf同位素研究及其构造意义[J].地质学报,95(4):1245-1259.
Sun Hongwei, Wang Jie, Ren Junping, Gu Alei, Zuo Libo, Liu Zijiang, Xing Shi, Su Xiaoyun, Alphet Phaskani DOKOWE, Ezekiah CHIKAMBWE.2021. Study of U- Pb chronology and Hf isotopes of detrital zircons from metamorphic supracrustal rocks in the central part of the Bangweulu block and its tectonic significance[J]. Acta Geologica Sinica,95(4):1245-1259.

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  • 收稿日期:2020-07-20
  • 最后修改日期:2020-08-12
  • 录用日期:2020-11-06
  • 在线发布日期: 2020-11-17
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