ABSTRACT

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).

摘要

寒武纪-奥陶纪太白山盆地位于朝鲜半岛中东部的中朝地块（华北克拉通）的前寒武纪基底之上。这对应于全球公认的寒武纪大不整合面发生海侵。然而，早寒武世-奥陶世中朝地块的古地理尚不清楚。本研究旨在确定中朝地块东部的物源并重建古地理。为此，我们使用从丹阳（即长山）、旌善和东亭地区采集的样品研究了下寒武统-奥陶统序列中碎屑锆石的 U-Pb 年龄。来自所有样品的碎屑锆石清楚地显示出古元古代（约 1875-1861 Ma）和一个小群新太古代（约 2500 Ma）。下部石英岩（长山组和旌善组）的年龄谱与太白山盆地的年龄谱有部分区别，显示出双峰前寒武纪峰，表明中韩地块内优选的排水系统。代表下部石英岩中最大沉积年龄的年轻碎屑锆石年龄的缺乏表明火成岩活动很少，外部碎屑很少流入。相比之下，下层石英岩的年龄谱与一致上覆的页岩（即~510 Ma Myobong 组）的年龄谱不同，主要由来自东冈瓦纳的新中元古代碎屑锆石组成。上层石英岩（Dongjeom组）中的古元古代碎屑锆石重复占优势，无新元古代碎屑锆石。占主导地位的古元古代锆石的重新出现很可能与可能由于古亚洲洋（PAO）俯冲引起的隆起有关。我们认为，无论寒武纪-最早奥陶纪（约 480-500 Ma）期间全球海侵如何，沿中朝地块东缘的渐进变化都受到区域构造作用的影响。