Basement–cover relationships of the Kalak Nappe Complex, Arctic Norwegian Caledonides and constraints on Neoproterozoic terrane assembly in the North Atlantic region
Basement–cover relationships of the Kalak Nappe Complex, Arctic Norwegian Caledonides and constraints on Neoproterozoic terrane assembly in the North Atlantic region
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DOI：
10.1016/j.precamres.2007.07.006
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发表时间：
2008-02
影响因子：
3.8
通讯作者：
C. Kirkland;J. Daly;M. Whitehouse
中科院分区：
文献类型：
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作者：
C. Kirkland;J. Daly;M. Whitehouse
卡拉克推覆杂岩（KNC）被认为是加里东造山运动期间向东叠套到波罗的海（芬诺斯堪的纳维亚）地盾上的波罗的海被动边缘变质沉积物。最近的研究质疑了这种解释，而是指向新元古代的外来起源。为了解决这一争议，我们提出了一个Sm-Nd和U-Th-Pb的研究，传统上被认为是沉积基底，沿着与盖层岩沉积物和侵入岩的格涅西奇单位。KNC下面的晚古元古代片麻岩沉积于1948± 33 Ma之后，在1796± 3 Ma Tjukkfjellet花岗岩侵入之前，并受到后来1765±9和1727± 9 Ma熔融事件的影响。这些片麻岩被解释为波罗的海地盾的一部分，位于KNC的下方，穿过构造接触。KNC的砂岩和其他副片麻岩以前被认为是其前寒武纪基底之间的不整合被重新解释为新元古代变质沉积之间的修改沉积接触。这些变质沉积物具有统计上非常相似的碎屑锆石群，其年龄分别为1034±22、1025±32和1014± 14 Ma。结果表明，KNC沉积物沉积在新元古代盆地沿着劳伦特边缘东部Rodinia和没有连接到波罗的海通过沉积基底。851± 5 Ma的Eidvågvatnet和853± 4 Ma的Nordneset花岗岩的年龄表明，与Porsanger造山运动有关的侵入物质（c. 850 Ma）影响了KNC河上游相当大的区域。新元古代晚期（711±6、687±12和617± 6 Ma）的事件也被确认，其中最晚的事件可能是裂谷作用的表现。新元古代早期岩浆活动（c. 840- 690 Ma）的发现，这些结果支持了KNC陨石的外来起源。
The Kalak Nappe Complex (KNC) has been regarded as Baltica passive margin metasediments telescoped eastwards onto the Baltic (Fennoscandian) Shield during the Caledonian Orogeny. Recent studies have questioned this interpretation, instead pointing to a Neoproterozoic exotic origin. In an effort to resolve this controversy we present a Sm–Nd and U–Th–Pb study of gnessic units, traditionally considered as the depositional basement, along with cover rock sediments and intrusives. Late Palaeoproterozoic gneisses now beneath the KNC were deposited after 1948±33Ma, before intrusion of the Tjukkfjellet Granite at 1796±3Ma, and were affected by later melting events at 1765±9 and 1727±9Ma. These gneisses are interpreted as part of the Baltic Shield and underlie the KNC across a tectonic contact. An unconformity between psammites of the KNC and other paragneisses previously considered as its Precambrian basement is reinterpreted as a modified sedimentary contact between Neoproterozoic metasediments. These metasediments have statistically very similar detrital zircon populations with grains as young as 1034±22, 1025±32 and 1014±14Ma. The results indicate that the KNC sediments were deposited during the Neoproterozoic in basins along the Laurentian margin of eastern Rodinia and were not connected to Baltica via a depositional basement. Dating of the 851±5Ma Eidvågvatnet and 853±4Ma Nordneset granites shows that intrusive material associated with the Porsanger Orogeny (c. 850Ma) affected a considerable region of the upper KNC terrane. Later Neoproterozoic events at 711±6, 687±12 and 617±6Ma are also recognised the latest of which may be an expression of rifting. Since early Neoproterozoic magmatism (c. 840–690Ma) is unknown in Baltica, these results support an exotic origin for the KNC terranes.