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首页> 外文期刊>Journal of Asian earth sciences >Zircon SHRIMP U-Pb dating of metamorphic complexes in the conjunction of the Greater and Lesser Xing'an ranges, NE China: Timing of formation and metamorphism and tectonic implications
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Zircon SHRIMP U-Pb dating of metamorphic complexes in the conjunction of the Greater and Lesser Xing'an ranges, NE China: Timing of formation and metamorphism and tectonic implications

机译：中国东北大兴安岭与小兴安岭交界处的锆石SHRIMP U-Pb变质复合物年代学：形成，变质的时间和构造意义

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Metamorphic complexes, including the Luomahu, Xinkailing and Fengshuigouhe groups, are scattered in the conjunction of the Greater and the Lesser Xing'an ranges, NE China, and have long been interpreted to represent the Precambrian basement of the so-called "Xing'an" and "Songnen" blocks although reliable evidence is lacking. Thin-section examination and mineral assemblage indicate that the protoliths of these metamorphic rocks are mainly meta-sedimentary and meta-volcanic rocks and have experienced greenschist- to amphibolite-facies metamorphism and strong deformation. Zircon SHRIMP U-Pb dating results of the metamorphic complexes and associated pre- or syn-kinematic veins constrained the formation and metamorphic ages of the Luomahuo Group at 175 +/- 3 Ma and 159 +/- 3 Ma, the Xingkailing Group at 200 +/- 2 Ma and 158 +/- 3 Ma, and the Fengshuigouhe Group at between 230-310 Ma and 170 +/- 3 Ma, respectively. Additionally, all these rocks contain some Late Paleozoic detrital or inherited zircons with ages between 290-390 Ma, but no Precambrian, even if Early Paleozoic, age information was detected from these metamorphic rocks. These new data suggest that the metamorphic complexes were formed during Mesozoic-Late Paleozoic period, rather than in Precambrian as previously inferred, and that all of them underwent metamorphism and deformation during Middle Jurassic between 170-160 Ma. Consequently, these metamorphic complexes are not basement rocks of the so-called Precambrian continental blocks. Instead, there are likely metamorphosed Late Paleozoic-Mesozoic accretionary complexes and/or arc terranes. These results, in combination with published data, illustrate an overall young trend from north to south in the tectonic evolution of the northern Xing'an region. Significantly, the Jurassic (170-160 Ma) metamorphism and deformation event firstly identified by this study from the metamorphic complexes likely recorded the coinstantaneous Mongol-Okhotsk collisional and thrusting event, implying the northern Xing'an region was in the fore-land setting during Middle Jurassic. The metamorphic complexes in the study area are either remnants of the detachment zones of the thrusting system or results of the far-field response of the collision event. (C) 2014 Elsevier Ltd. All rights reserved.
机译：包括罗麻湖组，新开岭组和风水沟河组在内的变质复合体散布在中国东北兴安山脉的较大范围和较小范围内，长期以来被解释为代表所谓“兴安”的前寒武纪基底。和“ Songnen”字样，但缺乏可靠的证据。薄层检查和矿物组合表明，这些变质岩的原岩主要为准沉积和准火山岩，经历了绿片岩-闪石相变质作用和强烈变形。 Zircon SHRIMP U-Pb变质复合体和相关的运动前或运动学脉变的约会结果限制了罗开火群在175 +/- 3 Ma和159 +/- 3 Ma（兴凯凌群在200时）的形成和变质年龄。 +/- 2 Ma和158 +/- 3 Ma，风水沟河群分别在230-310 Ma和170 +/- 3 Ma之间。此外，所有这些岩石都包含一些年龄在290-390 Ma之间的晚古生代碎屑岩或继承的锆石，但是从这些变质岩中即使检测到早古生代，也没有前寒武纪的年龄信息。这些新数据表明，这些变质复合体是在中生代晚期古生代形成的，而不是像以前推断的那样在前寒武纪形成的，而且它们都在中侏罗世170-160 Ma之间经历了变质和变形。因此，这些变质复合体不是所谓的前寒武纪大陆块的基底岩石。相反，可能有变质的晚古生代-中生代增生复合体和/或弧形地层。这些结果与已发表的数据相结合，说明了兴安北部地区构造演化中从北到南的总体年轻趋势。重要的是，这项研究首先从变质复合体中发现了侏罗纪（170-160 Ma）的变质和变形事件，这可能记录了蒙古-鄂霍次克州共生的碰撞和逆冲事件，暗示兴安北部地区在此期间处于前陆环境。中侏罗纪。研究区的变质复合体要么是冲断系统分离区的残余物，要么是碰撞事件的远场响应的结果。 （C）2014 Elsevier Ltd.保留所有权利。

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