The North Penninic Bündnerschiefer and Flysch of the Prättigau (Swiss Alps) revisited

IF 1.8 2区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Wilfried Winkler
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Abstract

During the re-mapping of the area for the Geological Atlas of Switzerland, a significant stratigraphic unconformity was discovered in the North Penninic (Valais) Bündnerschiefer and the Flysch series of the northern Prättigau. It separates different units of the Cretaceous Bündnerschiefer from the Palaeogene Flysch. We explain this observation by a basin conversion from extension to compression, which caused the initial deformation of the Bündnerschiefer in an accretionary wedge. Interlinked return-flow has created a new heterogeneous substrate for the flysch sediments and explains the different types of unconformities. The basin conversion coincided with high-grade metamorphism in the vicinity of the the South Penninic suture and the Austroalpine units, and the increased exhumation in the Austroalpine nappe stack. Detrital zircon dating confirms also a change from European to Austroalpine detrital sources in the flysch sandstones. We discuss a palaeotectonic model leading to hP/lT metamorphism of the Bündnerschiefer in the Late Eocene (c. 42 Ma). It appears that the flysch formations were also involved, but to a lesser degree by tectonic deformation from the late Early Eocene onwards, as the pervasive folding characteristic of the Bündnerschiefer is absent. This has been followed by a phase of S-directed backfolding. During the Oligocene and Miocene, more extensive deformation occurred by SE to NW compression and finally by probable westward thrusting and folding. Our main theme is the transition from passive to active continental margins, which in Alpine plate tectonic framework corresponds to the transition to flysch sedimentation by basin conversion. Our results show that the simultaneity of the transition from extension to compression, as indicated by the accumulation of flysch, shifted in time from south to north in the Alpine Tethys.
重访普拉提高(瑞士阿尔卑斯山)的北宾尼尼布恩德施费尔和弗莱施河
在为《瑞士地质地图集》(Geological Atlas of Switzerland)重新绘制该地区地图的过程中,发现了北宾夕法尼亚州(瓦莱州)Bündnerschiefer地层和普莱蒂高北部Flysch地层中的一个重要地层不整合现象。它将白垩纪 Bündnerschiefer 和古近纪 Flysch 的不同单元分开。我们对这一现象的解释是,盆地从延伸转变为压缩,导致了增生楔中 Bündnerschiefer 的初始变形。相互连接的回流为 Flysch 沉积物创造了一个新的异质基底,并解释了不同类型的不整合。盆地转换与南宾夕法尼亚缝合线和奥斯特罗派单元附近的高级变质作用以及奥斯特罗派山系堆积层的隆升相吻合。碎屑锆石年代测定也证实了飞沙砂岩中的碎屑来源已从欧洲转变为奥斯特派。我们讨论了一个古构造模型,该模型导致了晚始新世(约 42 Ma)布恩德施费尔地区的 hP/lT 变质作用。从早始新世晚期开始,flysch地层似乎也受到了构造变形的影响,但程度较轻,因为Bündnerschiefer地层不存在普遍的褶皱特征。随后是 S 向反褶阶段。在渐新世和中新世期间,由于从东南到西北的压缩,发生了更广泛的变形,最后可能是向西的推覆和褶皱。我们的主题是从被动大陆边缘向主动大陆边缘的过渡,在阿尔卑斯板块构造框架中,这相当于通过盆地转换向飞沙沉积的过渡。我们的研究结果表明,在阿尔卑斯特提斯地区,从延伸到压缩的过渡(如蝇蛆沉积所示)在时间上从南向北转移。
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来源期刊
Swiss Journal of Geosciences
Swiss Journal of Geosciences 地学-地质学
CiteScore
4.50
自引率
12.90%
发文量
21
审稿时长
>12 weeks
期刊介绍: The Swiss Journal of Geosciences publishes original research and review articles, with a particular focus on the evolution of the Tethys realm and the Alpine/Himalayan orogen. By consolidating the former Eclogae Geologicae Helvetiae and Swiss Bulletin of Mineralogy and Petrology, this international journal covers all disciplines of the solid Earth Sciences, including their practical applications. The journal gives preference to articles that are of wide interest to the international research community, while at the same time recognising the importance of documenting high-quality geoscientific data in a regional context, including the occasional publication of maps.
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