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The East Greenland Caledonides occupy a crucial position in plate-tectonic reconstructions of the Late Mesoproterozoic to Early Neoproterozoic Grenville–Sveconorwegian belt. We present new field and isotopic data from the northern Stauning Alper which indicate that the 1050–930 Ma history of the area was characterized by deposition of extensive clastic sequences. Sources of detritus were dominated by rocks of Mesoproterozoic age, with only limited contributions from Archaean sources, suggesting deposition at a distance from the present Caledonian foreland. A Neoproterozoic granite (938±13 Ma) provides evidence for thermal perturbation at a time of extensional collapse and uplift recorded in NW Scotland, the Grenville Belt of Canada, Labrador and the Sveconorwegian of SW Sweden and southern Norway. Widespread anatexis in the northern Stauning Alper at c.  430–425 Ma resulted from both collisional melting and decompression melting on uplift contemporaneous with the early part of orogenic collapse of the Caledonian Fold Belt. Caledonian deformation was focused at the zone of most extensive granite emplacement. Isotopic evidence suggests that Caledonian granites, previously thought to be entirely post-kinematic, actually predate late Caledonian extension.

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Abstract. Sectors of orogenic belts that have undergone extension present opportunities for the study of contemporaneous styles of magmatism at contrasting structural levels. The Caledonian (Ordovician-Devonian) orogenic belt of northeast Greenland experienced widespread extensional collapse either synchronous with or immediately following continental collision and crustal thickening. Extension resulted in juxtaposition of structurally simple upper plate rocks of mainly low metamorphic grade with underlying lower plate rocks that record intense deformation and high-grade metamorphism. Caledonian intracrustal granitic rocks occur as migmatite complexes, networks of sheets and veins, and as major gently dipping sheeted complexes in the lower plate and as steep-sided, discordant plutons in the upper plate. Published geochemical and isotopic evidence supports the interpretation of these granitic rocks as a single intrusive suite formed by crustal anatexis that was initiated during crustal thickening and peak metamorphism and continued during decompression and extensional collapse. In this paper we test this hypothesis by the isotopic dating of two granite sheets from the lower plate and three plutons from the upper plate. These yield U-Pb zircon or monazite ages in the range -•431-428 Ma that are indistinguishable within error, thus demonstrating that granitic melt emplacement was contemporaneous at the contrasting structural levels. We conclude that at midcrustal levels, processes of magma segregation and transport were controlled by low-angle, noncoaxial extensional shear. Batches of magma were segregated tectonically and likely migrated updip as a result of tectonic pumping and buoyancy. These amalgamated to form synkinematic sheets in the lower plate that we interpret as the channelways by which magma was transported to higher

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NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kalsbeek, F., Nutman, A. P., Escher, J. C., Friderichsen, J. D., Hull, J. M., Jones, K. A., & Schack Pedersen, S. A. (1999). Geochronology of granitic and supracrustal rocks from the northern part of the East Greenland Caledonides: ion microprobe U–Pb zircon ages. Geology of Greenland Survey Bulletin, 184, 31-48. https://doi.org/10.34194/ggub.v184.5228 _______________ Granitoid rocks from different settings within the northern part of the East Greenland Caledonian 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.

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Sediment outliers in North-East Greenland are briefly described and dated on the basis of macro- and microscopic plant fossils. Conglomerates and sandstones at Depotnæsset are probably of Late Carboniferous age based on the content of poorly preserved spores and pollen together with Stigmaria molds. Conglomerates, sandstones and coals from localities west of Germania Land are of Early to Middle Jurassic age based on poorly preserved fossil leaves and sporomorphs. The sedimentary facies and the fossil content of the Upper Carboniferous sediments suggest that the transition between the continental Carboniferous basins of East Greenland and the marine basins of North Greenland was situated north of 78°N. The maturity of the sporomorphs suggests that the Upper Carboniferous basins subsided by 1.5–2 km in Late Carboniferous to Middle Jurassic time, whereas subsidence of the Jurassic basins was negligible.