Geochronology of granitic and supracrustal rocks from the northern part of the East Greenland Caledonides: ion microprobe U–Pb zircon ages
Geochronology of granitic and supracrustal rocks from the northern part of the East Greenland Caledonides: ion microprobe U–Pb zircon ages
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东格陵兰喀里多尼亚北部花岗岩和表壳岩石的地质年代学：离子微探针 U-Pb 锆石年龄
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
S. Pedersen
中科院分区：
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作者：
F. Kalsbeek;A. Nutman;J. C. Escher;J. D. Friderichsen;J. Hull;K. Jones;S. Pedersen
东格陵兰加里东期褶皱带北方部分不同背景的花岗岩类岩石的锆石U-Pb年龄在2000 ~ 1730 Ma之间，证实了结晶基底的古元古代起源。广泛的砂岩序列出现在加里东褶皱带和西部的前陆;所有这些都被分配到独立峡湾群，并在地质图上归属于中元古代。然而，加里东褶皱带中与砂岩共生的变流纹岩的年龄为1740 ± 6 Ma，比预期的要大得多。同一地区的砂岩样品的锆石年龄表明沉积结束后的古元古代造山事件，但在1740年前的流纹岩的侵位的一部分，从另一个地方的砂岩可能已经沉积前侵位的最新元古代花岗岩片。野外关系表明，一些花岗岩脉和岩片的年龄可能是加里东期的，但除了一个可能的例外，所有这些分析证明是元古代的。在东格陵兰加里东地区的北方明显缺乏加里东花岗岩，尽管区域高级变质，可能与缺乏主要的泥质表壳岩的结晶基底复合体。
Granitoid rocks from different settings within the northern part of the East Greenland Caledo-nian fold belt have yielded U–Pb zircon dates between 2000 and 1730 Ma, confirming the Palaeoproterozoic origin of the crystalline basement. Widespread sandstone sequences occur both in the Caledonian fold belt and in the foreland to the west; all of these have been assigned to the Independence Fjord Group, and attributed a Mesoproterozoic age on geological maps. However, metarhyolitic rocks associated with the sandstones in the Caledonian fold belt have yielded an age of 1740 ± 6 Ma, significantly older than anticipated. Zircon ages for a sandstone sample in the same area suggest deposition after the end of Palaeoproterozoic orogenic events, but in part prior to emplacement of the rhyolitic rocks at 1740 Ma; sandstone from another locality may have been deposited before emplacement of the latest Proterozoic granite sheets. Field relations suggest that some granitic veins and sheets might be Caledonian in age, but, with one possible exception, all those analysed proved to be Proterozoic. The apparent absence of Caledonian granites in the northern part of the East Greenland Caledonides, despite regional high-grade metamorphism, may be related to the lack of major occurrences of pelitic supracrustal rocks within the crystalline basement complexes.