北山造山带南带中元古代副变质岩的锆石U-Pb年代学和Hf同位素研究——对北山造山带南带前寒武纪物质演化的探索
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西北大学地质学系,西北大学地质学系,西北大学地质学系

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(编号:40602023,41072147)


Zircon U-Pb Chronology and Hf Isotopic Study on the Mesoproterozoic Metasedimentary Rocks: Insight into the Evolution of Precambrian Materials in the South Section of Beishan Orogen
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Department of Geology Northwest University,Department of Geology Northwest University,Department of Geology Northwest University

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    摘要:

    北山造山带位于中亚造山带南缘,主要由一系列俯冲增生杂岩体构成。在其宽缓的造山区内,零散地分布着前寒武纪岩石。由于古生代以来强烈的造山作用和随后的陆内造山作用的改造,造成北山内的前寒武纪岩石和古生代以来的造山带产物难以区分。因此,关于北山造山带内的前寒武系归属问题,一直以来争议很大。本文在详细野外地质工作的基础上,报道了位于北山造山带中部的马鬃山地块内前寒武纪副变质岩的岩相学、锆石UPb年代学和Hf同位素研究。该岩石较高的变质程度、岩石组合、碎屑锆石年龄谱特征均显示其和北山造山带内古生代的残余被动大陆边缘产物不同,属于北山造山带内残余的前寒武纪基底,且沉积时代在中元古代约1.1~1.45 Ga之间。结合前人的研究,得出以下认识:北山的前寒武纪物质在中元古(约1.0 Ga)之后,显示出和塔里木克拉通、蒙古地块均相似的特征,表明三者均卷入了Rodina超大陆的聚散事件。在中元古代及其之前(约1.1 Ga之前)则显示多源区的特征。本文中的北山造山带中元古代副变质岩显示了中元古代及其之前与塔里木克拉通不同,与蒙古地块相似的特征。锆石的Hf同位素分析进一步揭示了北山造山带前寒武纪副变质岩和敦煌地块均记录了古太古代中晚期的新生地壳加入事件,显示了与塔里木克拉通的差异。这也暗示了敦煌地块和北山造山带在中元古代(约1.45 Ga)之前可能具有统一的前寒武纪基底。

    Abstract:

    TheBeishan orogen, located in the southern Central Asia Orogenic Belt (CAOB), mainly consists of a series of subductionaccretionary complexes. Some Precambrian rocks are sporadically distributed within the wide accretionary zone of Beishan. Due to the metamorphism and deformation during the strong orogensis and subsequent intracontinental orogensis since the Paleozoic, it is difficult to distinguish the Precambrian rocks and the products of orogensis in Beishan. Thus, the Precambrian affinity in the Beishan orogen is still controversial. Based on detailed field work, we carried out petrographic, zircon U-Pb geochronological and Hf isotopic analysis on Precambrian metasedimentary rocks from the Mazongshan block in the central Beishan area. The relatively high metamorphic degree, rock assemblage and detrital zircon UPb age spectrum show significant differences from that of Paleozoic passive continental margin products, indicating that the metasedimentary rock in Beishan is remnant part of the Precambrian basement rocks formed between ~1.1 and 1.66 Ga. Combined with previous studies, the following understanding can be summarized: the Beishan area presents similar features as the Tarim and Mongolia blocks in material sources, suggesting that the three involved into the assembly and break-up event of the Rodina supercontinent after the Neoproterozoic, but show multiple sources before the Neoproterozoic (>1.1 Ga). The Mesoproterozoic parametamorphic rock in the Beishan orogen in this study shows that it is different from the Tarim craton, but similar to the Mongolia block. The Hf isotopic analysis further reveals that the Precambrian parametamorphic rocks and Dunhuang block in the Beishan orogenic belt all record the history of newborn crust event during the middle and late Paleoproterozoic and show differences from the Tarim craton. This also implies that the Dunhuang block and the beishan orogenic belt probably have a uniform Precambrian basement before the Mesoproterozoic (~1.58 Ga).

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周海,陈亮,孙勇.2018.北山造山带南带中元古代副变质岩的锆石U-Pb年代学和Hf同位素研究——对北山造山带南带前寒武纪物质演化的探索[J].地质学报,92(5):928-945.
ZHOU Hai, CHEN Liang, SUN Yong.2018. Zircon U-Pb Chronology and Hf Isotopic Study on the Mesoproterozoic Metasedimentary Rocks: Insight into the Evolution of Precambrian Materials in the South Section of Beishan Orogen[J]. Acta Geologica Sinica,92(5):928-945.

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  • 收稿日期:2017-04-11
  • 最后修改日期:2017-06-28
  • 录用日期:2017-07-10
  • 在线发布日期: 2018-05-11
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