华北克拉通南缘栾川群的形成时代、物源及其对区域构造演化的意义:锆石U- Pb年代学和Hf同位素制约
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本文为国家自然科学基金项目(编号41372194,41372123)和中国地质调查局地质调查项目(编号1211302108023- 1)资助成果。


Depositional age and provenance analysis of the Luanchuan Group in the southern margin of North China Craton and its significance for regional tectonic evolution:constraints from zircon U- Pb geochronology and Hf isotopes
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    摘要:

    栾川群沿秦岭造山带和华北克拉通两大构造单元的结合部分布,其时代归属和构造意义长期存在争议。本文从锆石U- Pb年代学和Hf同位素角度对栾川群进行物源分析和区域对比分析,为合理地理解华北克拉通南缘晚前寒武纪构造演化提供重要证据。栾川群上部大红口组浅变质粗面岩的结晶年龄为854±8Ma,成因以古元古代晚期陆壳物质的再循环或改造为主。栾川地区栾川群变碎屑岩中最年轻的碎屑锆石U- Pb年龄和大红口组浅变质粗面岩及相关侵入岩的结晶年龄限定栾川群沉积时代在917~844Ma,属于新元古代青白口纪。白术沟组中上部、煤窖沟组和鱼库组变碎屑岩的碎屑锆石U- Pb年龄和Hf同位素特征一致,碎屑锆石U- Pb年龄集中在1. 85~1. 10Ga之间,北秦岭地体是最可能的物源区;Hf两阶段模式年龄(TDM2)为1. 33~2. 92Ga,揭示源区经历了~1. 45Ga、~1. 8Ga、~2. 1Ga和~2. 5Ga四期元古代陆壳增生。栾川群白术沟组下部和白术沟组中上部至鱼库组之间截然不同的碎屑锆石年龄谱图表明白术沟组沉积期间物源区由华北克拉通转变为北秦岭块体,沉积构造背景由被动大陆边缘转化为碰撞造山和后碰撞伸展环境。北秦岭地体原来应属于华北克拉通的一部分,至少在华北克拉通南缘至东缘地区曾存在与北秦岭地体类似的中、新元古代构造带。该构造带强烈地参与了Columbia超大陆裂解和Rodinia超大陆汇聚及裂解过程,在新元古代早期与华北克拉通曾短暂的拼合并造山,转变为华北克拉通周缘沉积盆地的主要物源供给区。

    Abstract:

    There is a long- standing controversy about the depositional age and tectonic significance of the Luanchuan Group located between the tectonic units of the Qinling orogenic belt and the North China Craton (NCC). In this paper, the provenance and regional comparative analysis of Luanchuan Group from the perspective of zircon U- Pb chronology and Hf isotopes could provide important evidence of late Precambrian tectonic evolution in the southern margin of NCC. The crystallization age of epi- metamorphic trachyte from the Dahongkou Formation in the upper part of the Luanchuan Group is 854±8 Ma, and its petrogenesis is mainly due to the recycling of Late Paleoproterozoic continental crust. The depositional age of the Luanchuan Group is constrained between 917~844 Ma by the youngest clastic zircon U- Pb age of the metaclastic rocks of the Luanchuan Group and crystallization age of epi- metamorphic trachyte from the Dahongkou Formation and related intrusive rocks in the Luanchuan area, which belong to the Qingbaikou period. There are similar U- Pb ages and two- stage Hf model ages (TDM2) of detrital zircons amongst upper and middle parts of the Baishugou Formation, the Meijiaogou Formation and the Yuku Formation of the Luanchuan Group in the Luanchuan area. The U- Pb ages are mostly 1. 85 to 1. 10 Ga, which indicates that the North Qinling Terrane (NQT) was the most probable provenance, and TDM2 are between 1. 33~2. 92 Ga, which signifies that the provenance area has undergone 4 episodes of Proterozoic crustal accretion at ~1. 45 Ga, ~1. 8 Ga, ~2. 1 Ga and ~2. 5 Ga. The change in the provenance of Luanchuan Group from NCC to NQT and its sedimentary tectonic setting from passive continental margin to collisional orogeny and post- collisional extension environment during sedimentation of the Baishugou Formation are suggested by marked differences in the detrital zircon age spectrum between lower parts of the Baishugou Formation and other strata of the Luanchuan Group. A Meso- Neoproterozoic tectonic belt similar to the NQT, which essentially belongs to a part of the NCC, developed at least in the eastern and the southern margin of the NCC. The tectonic belt was strongly involved in the Columbia supercontinent breakup process and the Rodinia supercontinent convergence, and was briefly combined with the NCC during the early Neoproterozoic era to transform into main provenance for the peripheral sedimentary basin of the NCC.

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李振生,贾超,赵卓娅,霍金晶,李全忠,张交东.2020.华北克拉通南缘栾川群的形成时代、物源及其对区域构造演化的意义:锆石U- Pb年代学和Hf同位素制约[J].地质学报,94(4):1046-1066.
LI Zhensheng, JIA Chao, ZHAO Zhuoya, HUO Jinjing, LI Quanzhong, ZHANG Jiaodong.2020. Depositional age and provenance analysis of the Luanchuan Group in the southern margin of North China Craton and its significance for regional tectonic evolution:constraints from zircon U- Pb geochronology and Hf isotopes[J]. Acta Geologica Sinica,94(4):1046-1066.

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  • 收稿日期:2019-01-17
  • 最后修改日期:2019-03-19
  • 录用日期:2019-06-03
  • 在线发布日期: 2019-06-03
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