LIU Pinghua, ZOU Lei, TIAN Zhonghua, JI Lei, SHI Jianrong. Determination of Late Paleozoic metamorphic event in the Langshan area, western Inner Mongolia: New evidence from LA-ICP-MS zircon U-Pb dating of the Wulashan Group[J]. Geological Bulletin of China, 2019, 38(10): 1691-1710.
    Citation: LIU Pinghua, ZOU Lei, TIAN Zhonghua, JI Lei, SHI Jianrong. Determination of Late Paleozoic metamorphic event in the Langshan area, western Inner Mongolia: New evidence from LA-ICP-MS zircon U-Pb dating of the Wulashan Group[J]. Geological Bulletin of China, 2019, 38(10): 1691-1710.

    Determination of Late Paleozoic metamorphic event in the Langshan area, western Inner Mongolia: New evidence from LA-ICP-MS zircon U-Pb dating of the Wulashan Group

    • Wulashan Group is one of the important parts of the Precambrian basement in the Langshan area, and accurate determination of the diagenetic and metamorphic timing of the Wulashan Group is of great scientific significance for further discussing the Precambrian geological evolution of the Langshan area. In this paper, the authors carried out a detailed study of the petrological observation and zircon U-Pb dating of hornblende biotite plagioclase gneisses and related granitic leucosomes from Wulashan Group. The result of detrital zircon U-Pb dating and geological investigation of the hornblende biotite plagioclase gneisses indicates that the age of detrital zircons of the gneisses of the Wulashan Group in Langshan area ranges from 2591Ma to 1800Ma, and the youngest group age of detrital zircons is circa 1873Ma. Combined with its metamorphic age of circa 270Ma, it is preliminarily considered that the sedimentary age of the gneisses ranges from 1873Ma to 270Ma. The above and latest studies indicate that, besides Neoarchaean-Paleoproterozoic metamorphic rocks, there are also Mesoproterozoic-Late Paleozoic metasedimentary rocks within the Wulashan Group. The result of cathodoluminescence image analysis and U-Pb dating of zircons indicates that a large number of metamorphic zircons exist in the hornblende biotite plagioclase gneisses. They record a 206Pb/238U weighted average age of 269±4Ma, which represents the timing of the late Paleozoic amphibolite-facies metamorphism of the Wulashan Group in the Langshan area, probably in response to the Late Paleozoic collisional orogenesis between the North China Plate and Siberian Plate. In addition, a reliable 206Pb/238U weighted average age of 264±3Ma of the high-U zircons from the high-silica granitic leucosomes was obtained by pre-ablation dating method. The age (264±3Ma) is interpreted as the diagenetic timing of high-silica granitic leucosomes in the Wulashan Group, which represents the timing of the transformation for the collisional extrusion to post-collisional extension during late Paleozoic orogenesis.
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