COSC 2 – Constraints on age and setting of Proterozoic igneous and early Palaeozoic sedimentary rocks below and within the Caledonian nappe pile

COSC 2 â 对加里东推覆堆下方和内部元古代火成岩和早古生代沉积岩的年龄和环境的限制

• 批准号: 457735783
• 负责人: Professor Dr. Oliver Lehnert
• 金额: --
• 依托单位: University of Plymouth
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/457735783?language=en
• 关键词: COSC; Constraints; age; setting; Proterozoic

COSC 2 as part of the ‘Collisional Orogeny in the Scandinavian Caledonides’ (COSC) drilling project, represents an integral of the Swedish Scientific Drilling Program (SSDP) In the frame of the International Scientific Drilling Program (ICDP). As a consequence of the closure of the Iapetus Ocean and the corresponding continent-continent collision between Baltica and Laurentia during Early Palaeozoic times, the Baltoscandian margin was partially subducted beneath Laurentia in the mid-late Silurian forming a Himalayan-type orogen. The COSC project studies these processes, COSC 1 investigated the emplacement of high-grade metamorphic allochthons in the Åre area and COSC-2 aimed to study, based on seismic interpretations and geophysical models, a continuous Early Palaeozoic sedimentary succession, the main Caledonian décollement in the Cambrian Alum Shale succession and a Fennoscandian granitic basement. However, scientific drilling recorded an unexpected but very interesting core succession involving a thick volcanic sequence intruded by dolerite dykes instead of Palaeoproterozoic granitic basement. During drilling it was suggested that an imbricate zone with Proterozoic and Cambrian sandstones originating from different settings covers this basement, overlain by an deformed Alum shale comprising the main decollement followed by Early Palaeozoic siliciclastics succession formed in more outboard and deeper environments than assumed before. The detailed logging, however, showed that there is a continuous sedimentary succession on top of the weathered basement covered by a Protolith. A few meters of heterogenous sediments including some marls with trilobites, indicating a Lower Cambrian instead of Neoproterozoic age, display the “birth of a Cambrian basin” which starts to fill rapidly by mostly coarse grained sediment gravity flows before an interruption by a longer quiet period during most of the time of Alum Shale deposition followed by a turbitite sequence showing fining upward and general deepening. The succession was previously regarded as a foreland basin fill, but the local sources and the long time of sedimentation involved points to deposition in a pull apart basin which is well preserved beneath the Caledonian nappes. This exiting succession provides the possibility of detailed sedimentological, stratigraphic and geochemical studies. Dating of sedimentary units is most important for a stratigraphic framework and further correlations with geotectonic events, sea-level fluctuations, evolutionary pulses, climate change as well as for the re-interpretation of seismic models. The focus of this project provides the base for interdisciplinary investigations performed by different working groups of the COSC science team such as geochronology, geothermics, geology, and geophysics.

COSC 2是“斯堪的纳维亚加里东山脉碰撞造山”（COSC）钻探项目的一部分，是瑞典科学钻探计划（SSDP）在国际科学钻探计划（ICDP）框架内的一个组成部分。由于早古生代Iapetus洋的闭合以及波罗的海和劳伦大陆之间的陆-陆碰撞，波罗的海-斯堪的纳维亚边缘在志留纪中晚期部分俯冲到劳伦大陆之下，形成喜马拉雅型造山带。COSC项目研究这些过程，COSC 1调查了Alzere地区高级变质外来岩的就位情况，COSC-2旨在根据地震解释和地球物理模型研究一个连续的早古生代沉积序列、寒武纪明矾页岩序列中的主要加里东期滑脱和一个芬诺斯堪的纳维亚花岗岩基底。然而，科学钻探记录了一个意想不到但非常有趣的核心序列，涉及由粗玄岩脉侵入的厚火山序列，而不是古元古代花岗岩基底。在钻井过程中，有人建议，一个叠瓦状带与元古代和寒武纪砂岩起源于不同的设置覆盖这个基底，由变形明矾页岩覆盖，包括主要滑脱层，其次是早古生代硅质碎屑序列形成在更外侧和更深的环境比以前假设的。然而，详细的测井表明，在被原岩覆盖的风化基底顶部存在连续的沉积序列。几米的非均质沉积物，包括一些带有三叶虫的泥灰岩，表明是下寒武纪而不是新元古代，显示出“寒武纪盆地的诞生”，在明矾页岩沉积的大部分时间内，在被一个较长的平静期中断之前，大部分粗颗粒沉积物重力流开始迅速填充，随后是一个浊流序列，显示出向上变细和普遍加深。该序列以前被认为是一个前陆盆地填充，但当地的来源和长期的沉积涉及点沉积在一个拉分盆地，这是保存完好的加里东推覆体之下。这一现存的层序为详细的沉积学、地层学和地球化学研究提供了可能。沉积单元的定年对于地层格架和与大地构造事件、海平面波动、演化脉冲、气候变化的进一步关联以及地震模型的重新解释是最重要的。该项目的重点为COSC科学团队的不同工作组进行的跨学科调查提供了基础，如地质年代学，地质学，地质学和地球物理学。