Abstract

Detrital zircon dating allows us to elucidate the age and provenance of siliciclastic strata of the Sarydjaz and Ichkebash formations in the Middle Tianshan of eastern Kyrgyzstan, previously thought to be of the Middle or Late Ordovician age. New data indicate that the upper part of the Ichkebash Formation contains Lower Silurian sediments, previously unknown in this region. The Kanachu Formation, which lies stratigraphically above, is also not older than the Silurian in age. The absence of marine fauna at these levels apparently reflects the predominant development of deltaic facies. The paleocurrent indicators and the ages of detrital zircons point to its provenance in the North Tianshan (NTSh). Grains with ages from the Late Cambrian to the Silurian, synchronous with the main stage of the Early Paleozoic magmatism in the NTSh, predominate in the Ichkebash Formation. The occurrence of Precambrian detrital zircons in all dated samples and especially in the Sarydjaz Formation indicates the erosion of Precambrian rocks. The provenance most likely located in the Chu-Kendyktas Massif, where the Precambrian detrital zircons in the Neoproterozoic and Early Paleozoic metasedimentary rocks demonstrate a similar distribution of the ages. The foredeep in the Middle Tianshan was formed in the Late Ordovician and Early Silurian generally subsynchronously with the main orogenic event in the NTSh.

中文翻译：

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中天山（吉尔吉斯斯坦东部）奥陶纪和志留纪硅质碎屑地层：根据碎屑锆石测年的年龄和物源

摘要

碎屑锆石测年使我们能够阐明吉尔吉斯斯坦东部中天山 Sarydjaz 和 Ichkebash 地层硅质碎屑地层的年龄和来源，此前人们认为该地层属于中奥陶世或晚奥陶世。新数据表明，Ichkebash 地层上部含有下志留统沉积物，此前该地区未知。地层上方的卡纳丘组（Kanachu Formation）的年龄也不比志留纪更老。这些层面上缺乏海洋动物群显然反映了三角洲相的主要发育。古水流指标和碎屑锆石年龄表明其起源于北天山（NTSh）。伊奇克巴什组中以晚寒武世至志留纪时期的颗粒为主，与NTSh早古生代岩浆作用的主要阶段同步。在所有测年样本中，特别是在 Sarydjaz 地层中，都出现了前寒武纪碎屑锆石，这表明前寒武纪岩石受到了侵蚀。物源最有可能位于 Chu-Kendyktas 地块，其中新元古代和早古生代变质沉积岩中的前寒武纪碎屑锆石表现出类似的年龄分布。中天山前渊形成于晚奥陶世和早志留世，与新台山主要造山事件大致同步。