Geochronology of granitic and supracrustal rocks from the northern part of the East Greenland Caledonides: ion microprobe U–Pb zircon ages

Abstract

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
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 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.

U‐Pb zircon dating of metaigneous rocks from the Nordbreen Nappe of Svalbard’s Ny‐Friesland suggests their affinity to Northeast Greenland

“…Felsic metavolcanic rocks of ca. 1,740 Ma age are also known from the Hekla Sund and Aage Berthelsen Gletscher formations of the Independence Fjord Group in Kronprins Christian Land (KCL on Figure ), the northernmost part of the East Greenland Caledonides (Kalsbeek et al, ). The metavolcanic rocks are intercalated with a 2 km thick package of siliciclastic rocks of inferred Palaeoproterozoic age (Collinson, Kalsbeek, Jepsen, Pedersen, & Upton, ; Higgins, ).…”

“…1,750 Ma basement province extending ~800 km north of 73°N along the east coast of Greenland (e.g. Kalsbeek, Higgins, Jepsen, Frei, & Nutman, ; Kalsbeek et al, ). Felsic metavolcanic rocks of ca.…”

The Neoproterozoic Rivieradal Group of Kronprins Christian Land, eastern North Greenland

“…Note that the traditional interpretation of the allochthonous quartzites as equivalents of the foreland Independence Fjord Group (as depicted here and on Fig. 2), has been brought into doubt by the 1740 Ma age on interbedded rhyolites (see discussion in Kalsbeek et al 1999 andPedersen et al 2002).…”

“…The Vandredalen thrust sheet, in turn, is structurally overlain by a thrust sheet that transported Palaeoproterozoic to Mesoproterozoic clastic and volcanic rocks westwards. The allochthonous quartzites have traditionally been viewed as equivalents of the Independence Fjord Group on the foreland (see Figs 1, 2), but SHRIMP isotopic studies on rhyolites interbedded with the quartzites that yielded an age of 1740 Ma (Kalsbeek et al 1999) have cast some doubt on this interpretation (see also Pedersen et al 2002). Still farther to the east, higher thick-skinned thrust sheets incorporate crystalline basement gneisses.…”

The Eleonore Sø and Målebjerg foreland windows, East Greenland Caledonides, and the demise of the ‘stockwerke’ concept

“…The former have yielded Archaean and Proterozoic protolith ages, with Archaean gneiss complexes extending throughout the inner part of the Scoresby Sund region and northwards to southern Suess Land (72°50′N). Farther north the orthogneisses have yielded Palaeoproterozoic protolith ages which relate to an important episode of regional Palaeoproterozoic crustformation well documented throughout the northern half of the East Greenland Caledonides (Kalsbeek et al 1993(Kalsbeek et al , 1999. It follows that Haller (1953) was wrong in attributing the formation of the orthogneisses to rising fronts of Caledonian migmatisation that transformed metasedimentary rocks of the Eleonore Bay 'Formation'.…”