Detrital zircon signature of the Moine Supergroup, Scotland: contrasts and comparisons with other Neoproterozoic successions within the circum-North Atlantic region
Detrital zircon signature of the Moine Supergroup, Scotland: contrasts and comparisons with other Neoproterozoic successions within the circum-North Atlantic region
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苏格兰莫因超群的碎屑锆石特征：与环北大西洋地区其他新元古代序列的对比和比较
DOI：
10.1016/j.precamres.2008.01.003
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发表时间：
2008
影响因子：
3.8
通讯作者：
A. Prave
中科院分区：
文献类型：
--
作者：
C. Kirkland;R. Strachan;A. Prave
利用离子探针对苏格兰西北部新元古代莫因超群3个不同地层样品的200粒碎屑锆石颗粒进行了分析。样品取自最古老的莫因单元Morar组的下、上沙梅特组，以及构造地层学上较年轻的Glenfinnan组。Morar组以古元古代和中元古代晶体和少量太古宙颗粒为主，而Glenfinnan组的总体年龄范围大致相同，但Grenville（晚中元古代）碎屑的比例较大。这些数据表明，格伦维尔时代的碎屑向上剖面增加，物源为劳伦，与格伦维尔造山带发育和发掘的最后阶段开始的莫因沉积相一致。最年轻的和和碎屑锆石为Morar群（1022±24Ma）和Glenfinnan群（1009±22Ma）提供了最大沉积年龄。沉积作用必须在842±20Ma之前停止，这是一个Morar组样品中岩浆锆石过度生长所记录的高温条件的年龄；这与中新元古代的诺达尔造山事件相吻合，在莫因超群的其他地方也有记载。通过对摩因碎屑锆石年龄分布与其他地区新元古代地层锆石年龄分布的统计比较，确定了三个主要的岩石构造单元：(1)中元古代晚期至新元古代早期盆地，含一系列晚期Grenville侵入岩；(2)新元古代中晚期与罗丁尼亚内伸展相关的盆地或与罗丁尼亚洋缘相接的盆地；(3)新元古代晚期至古生代早期盆地形成于罗迪尼亚断裂主期。统计比较表明：(1)在苏格兰，Morar群与次格兰平原群（Dava-Glen Banchor序列）相似，与加里东前陆的Torridonian组（applcross组和Ault Bea组）有联系，但与Moinian Glenfinnan组和Loch Eil组以及Dalradian组差异显著；（ii） Moine的物源信号和沉积时间与挪威北部的Sørøy序列和东格陵兰岛的Eleonore湾下超群非常接近。所有这些都有一个劳伦的亲和力，因此构造模型调用一个地质上的异国情调的状态（即，一个terrane）为摩因似乎没有必要。
A total of 200 detrital zircon grains from three stratigraphically distinct samples of the Neoproterozoic Moine Supergroup, NW Scotland were analysed by ion microprobe. Samples were taken from the Lower and Upper Psammite Formations of the oldest Moine unit, the Morar Group, and one from the tectonostratigraphically overlying, and presumed younger, Glenfinnan Group. The Morar Group is dominated by Palaeo- and Mesoproterozoic crystals and minimal Archaean grains whereas the Glenfinnan Group has broadly the same overall age range but a greater proportion of Grenville (late Mesoproterozoic) detritus. These data indicate an increase up-section in Grenville-age detritus and a Laurentian provenance, consistent with initiation of Moine deposition during the final stages of development and exhumation of the Grenvillian Orogen. The youngest concordant detrital zircons provide maximum depositional ages for the Morar Group at 1022±24Ma and for the Glenfinnan Group at 1009±22Ma. Sedimentation must have ceased prior to 842±20Ma, the age of high temperature conditions recorded by magmatic zircon overgrowths in one of the Morar Group samples; this is compatible with mid-Neoproterozoic Knoydartian orogenic events documented elsewhere within the Moine Supergroup. Robust statistical comparison of the Moine detrital zircon age distributions to those from Neoproterozoic successions elsewhere enable definition of three main lithotectonic units: (1) late Mesoproterozic to early Neoproterozoic basins with a range of late Grenville intrusives; (2) mid- to late Neoproterozoic basins in extension-related intra-Rodinia settings or fringing Rodinia's oceanic margin; and (3) late Neoproterozoic to early Palaeozoic basins formed during the main phase of Rodinia break-up. Statistical comparisons also indicate that: (i) in Scotland, the Morar Group rocks are similar to the sub-Grampian Group rocks (Dava–Glen Banchor succession) and permit linkage with the Torridonian of the Caledonian foreland (Applecross and Ault Bea formations), but differ significantly from the Moinian Glenfinnan and Loch Eil groups, as well as the Dalradian rocks; and (ii) the provenance signal and depositional timing of the Moine compares closely to the Sørøy Succession of Arctic Norway and the lower Eleonore Bay Supergroup of East Greenland. All of these have a Laurentian affinity and thus tectonic models invoking a geologically exotic status (i.e., a terrane) for the Moine appear unnecessary.