A fluvial origin for the Neoproterozoic Morar Group, NW Scotland; implications for Torridon–Morar Group correlation and the Grenville Orogen foreland basin
A fluvial origin for the Neoproterozoic Morar Group, NW Scotland; implications for Torridon–Morar Group correlation and the Grenville Orogen foreland basin
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苏格兰西北部新元古代莫拉尔群的河流起源；对托里登-莫拉尔群对比和格伦维尔造山带前陆盆地的影响
DOI：
10.1144/0016-76492007-076
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发表时间：
2008
影响因子：
2.7
通讯作者：
D. Cheer
中科院分区：
文献类型：
--
作者：
M. Krabbendam;T. Prave;D. Cheer
前寒武纪沉积序列很难确定年代和对比。在苏格兰高地，加里东造山带前陆的厚而未变形的硅质碎屑“托里多尼亚”序列与加里东造山带内高度变形变质的硅质碎屑莫因序列之间的潜在相关性一直引起地质学家的兴趣。对萨瑟兰新元古代Altnaharra组（Morar组，最低Moine超群）进行了新的详细测绘，发现了保存完好的沉积特征的低应变带。该地层由3-5公里粗、厚层状沙土组成，具有丰富的巢状槽和平面交错层理，形成了米尺度的河道。古海流方向大致为北东-东偏东单峰。我们将阿尔特纳哈拉组解释为高能辫状河流沉积。Altnaharra组与未变质的新元古代applecro - aulbea组（Torridon组）在岩性、地层厚度、沉积学、地球化学、碎屑锆石年龄和太古宙基底地层位置等方面相似。这两个序列的沉积年龄限制重叠，并与格伦维尔晚期造山活动同时发生。碎屑锆石暗示了格伦维尔造山带相似的源区。因此，Morar群和Torridon群可以跨越加里东运动逆冲进行对比，最好的解释是作为一个单一的、大型的、与格伦维尔造山带平行的前陆盆地的一部分。
Precambrian sedimentary successions are difficult to date and correlate. In the Scottish Highlands, potential correlations between the thick, undeformed siliciclastic ‘Torridonian’ successions in the foreland of the Caledonian Orogen and the highly deformed and metamorphosed siliciclastic Moine succession within the Caledonian Orogen have long intrigued geologists. New and detailed mapping of the Neoproterozoic Altnaharra Formation (Morar Group, lowest Moine Supergroup) in Sutherland has discovered low-strain zones exhibiting well-preserved sedimentary features. The formation comprises 3–5 km of coarse, thick-bedded psammite with abundant nested trough and planar cross-bedding bedforms, defining metre-scale channels. Palaeocurrent directions are broadly unimodal to the NNE–ENE. We interpret the Altnaharra Formation as high-energy, braided fluvial deposits. The Altnaharra Formation and the unmetamorphosed, Neoproterozoic Applecross–Aultbea formations (Torridon Group) are similar in terms of lithology, stratigraphical thickness, sedimentology, geochemistry, detrital zircon ages and stratigraphical position on Archaean basement. Depositional age constraints for both successions overlap and are coeval with late Grenvillean orogenic activity. Detrital zircons imply similar source regions from the Grenville Orogen. The Morar and Torridon groups can thus be correlated across the Caledonian Moine Thrust and are best explained as parts of a single, large-scale, orogen-parallel foreland basin to the Grenville Orogen.