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Abstract <p>The results of U–Pb (SHRIMP) geochronological study enable to substantiate the ages of the key magmatic complexes in the Burkhan anticlinorium (BA) of the North Tianshan (NTS). Metarhyolites of the Tegerekkol Member, which represents the middle of three levels of felsic volcanic rocks in the Mesoproterozoic section of the BA, yielded an age of 1138 ± 7 Ma. The timing of volcanism corresponds to the episode of emplacement of the oldest ca 1160–1120 Ma Mesoproterozoic granites in the Kochkorka and Makbal anticlinoria in the north and northwest of the NTS. Similar geochemical characteristics of the volcanic rocks in the BA and the granites in the Makbal area suggest that they represent products of similar parental melts. The time of epidote-amphibolite metamorphism in the Tegerekkol Member can be estimated in the range of ca 1140–1080 Ma based on the age of metarhyolite and the Pb–Pb age of weakly metamorphosed limestones that lie unconformably above. The post-kinematic granodiorite of the Djamanechke intrusion, previously considered Mesoproterozoic, yielded an age of 478 ± 5 Ma. Older ages obtained by previous multigrain zircon analyses may reflect the presence of ca 1140 Ma inherited old cores and zircon xenocrysts, which were likely derived from volcanic rocks of the Tegerekkol Member surrounding the intrusion. Considering the age of the youngest granite-gneisses that experienced ductile deformation and the established age of undeformed granodiorite, the timing of the latest metamorphic episode in the BA is estimated in the range of ~494–478 Ma. This corresponds to the age of a major structural and metamorphic event, broadly expressed in the NTS at the beginning of the Early Ordovician.</p>

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Age and Tectonic Position of Mesoproterozoic Rhyolites and Early Ordovician Granites in the Burkhan Anticlinorium of the North Tianshan (Eastern Kyrgyzstan)

  • 期刊论文

  • 发表日期：

    2025年5月16日

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  • D. V. Alexeiev,
  • A. V. Kushnareva,
  • A. K. Khudoley,
  • V. V. Shatov,
  • A. A. Tretyakov

摘要

Abstract

The results of U–Pb (SHRIMP) geochronological study enable to substantiate the ages of the key magmatic complexes in the Burkhan anticlinorium (BA) of the North Tianshan (NTS). Metarhyolites of the Tegerekkol Member, which represents the middle of three levels of felsic volcanic rocks in the Mesoproterozoic section of the BA, yielded an age of 1138 ± 7 Ma. The timing of volcanism corresponds to the episode of emplacement of the oldest ca 1160–1120 Ma Mesoproterozoic granites in the Kochkorka and Makbal anticlinoria in the north and northwest of the NTS. Similar geochemical characteristics of the volcanic rocks in the BA and the granites in the Makbal area suggest that they represent products of similar parental melts. The time of epidote-amphibolite metamorphism in the Tegerekkol Member can be estimated in the range of ca 1140–1080 Ma based on the age of metarhyolite and the Pb–Pb age of weakly metamorphosed limestones that lie unconformably above. The post-kinematic granodiorite of the Djamanechke intrusion, previously considered Mesoproterozoic, yielded an age of 478 ± 5 Ma. Older ages obtained by previous multigrain zircon analyses may reflect the presence of ca 1140 Ma inherited old cores and zircon xenocrysts, which were likely derived from volcanic rocks of the Tegerekkol Member surrounding the intrusion. Considering the age of the youngest granite-gneisses that experienced ductile deformation and the established age of undeformed granodiorite, the timing of the latest metamorphic episode in the BA is estimated in the range of ~494–478 Ma. This corresponds to the age of a major structural and metamorphic event, broadly expressed in the NTS at the beginning of the Early Ordovician.