U-Pb ages of detrital zircons in lower Palaeozoic quartzites of the Taebaeksan Basin, eastern Sino–Korean Block: sediment provenance response to relative sea-level changes

The Cambrian–Ordovician Taebaeksan Basin overlies the Precambrian basement of the Sino–Korean Block (North China Craton) in the central–eastern Korean peninsula. This corresponds to the occurrence of the global marine transgression over the Great Unconformity in the Cambrian, which is widely recognized. However, the palaeogeography of the Sino–Korean Block during the Early Cambrian–Ordovician remains unclear. This study aimed to identify the provenances and reconstruct the palaeogeography of the eastern Sino–Korean Block. For this purpose, we investigated U-Pb ages of detrital zircons in the lower Cambrian–Ordovician successions using samples collected from the Danyang (i.e. Jangsan), Jeongseon, and Dongjeom areas. Detrital zircons from all samples clearly exhibited predominant clusters of Paleoproterozoic ages (ca. 1875–1861 Ma) and a minor cluster of Neoarchean ages (ca. 2500 Ma). The age spectra from the lower quartzites (Jangsan and Jeongseon formations) are partly distinguished from those in the Taebaeksan Basin, showing bimodal Precambrian peaks, which indicates the preferred drainage system within the Sino–Korean Block. A lack of young detrital zircon ages representing maximum depositional ages in the lower quartzites indicates that there were little igneous activity and little influx of external detritus. The age spectra from the lower quartzites, in contrast, are different from those of the conformably overlying shale (i.e. ~510 Ma Myobong Formation) consisting mainly of Neo–Mesoproterozoic detrital zircons derived from East Gondwana. Paleoproterozoic detrital zircons in the upper quartzite (Dongjeom Formation) were repetitively predominant without Neoproterozoic detrital zircons. The reappearance of predominant Paleoproterozoic zircons is most likely associated with uplifts possibly due to the subduction of the Paleo-Asian Ocean (PAO). We suggest that progressive changes along the eastern margin of the Sino–Korean Block were affected by the regional tectonism, regardless of the global transgression during the Cambrian–earliest Ordovician (ca. 480–500 Ma).

寒武纪-奥陶纪（Cambrian–Ordovician）太白盆地（Taebaeksan Basin）覆于朝鲜半岛中东部中朝地块（Sino–Korean Block，即华北克拉通North China Craton）的前寒武纪基底（Precambrian basement）之上。这与全球海侵（marine transgression）在寒武纪越过巨大不整合面（Great Unconformity）的公认现象相符。然而，早寒武世-奥陶纪期间中朝地块的古地理（palaeogeography）格局仍不明确。本研究旨在明确中朝地块东部的物源区，并重建其古地理格局。为此，我们对取自丹阳（即长山组Jangsan Formation）、旌善和东染地区的下寒武统-奥陶系地层序列样品，开展了碎屑锆石（detrital zircons）U-Pb年龄分析。所有样品的碎屑锆石均显示出以古元古代（Paleoproterozoic）年龄（约1875~1861 Ma）为主的峰值群，以及少量新太古代（Neoarchean）年龄（约2500 Ma）的峰值群。下石英岩（长山组和旌善组）的年龄谱与太白盆地的其他样品存在部分差异，呈现出双峰式前寒武纪年龄峰值，这指示中朝地块内部存在优势水系系统（drainage system）。下石英岩中缺乏代表最大沉积年龄（maximum depositional ages）的年轻碎屑锆石年龄，表明当时区域岩浆活动微弱，且外部碎屑物输入极少。与之相反，下石英岩的年龄谱与整合覆于其上的页岩（即约510 Ma的妙香山组Myobong Formation）截然不同，后者的碎屑锆石主要源自东冈瓦纳（East Gondwana），以新-中元古代（Neo–Mesoproterozoic）年龄为主。上石英岩（东染组Dongjeom Formation）中的古元古代碎屑锆石仍占绝对优势，且未出现新元古代碎屑锆石。这种古元古代锆石占主导的现象极有可能与古亚洲洋（Paleo-Asian Ocean, PAO）俯冲引发的隆升作用相关。我们认为，尽管寒武纪至早奥陶世（约480~500 Ma）存在全球海侵，中朝地块东缘的渐进式构造演化仍受区域构造作用的控制。