The oldest part of the Rae craton identified in western Greenland

Abstract

New U-Pb zircon data from a range of Archean rocks from the Paleoproterozoic Rinkian Belt in the North-West and central West Greenland provide new constraints on the crystallisation and formation of the Archean basement to this Paleoproterozoic orogen. The results show that the protoliths of the oldest orthogneisses were emplaced in the central part of the Rinkian Belt at c. 3150–3100 Ma. This was followed in the southern part of the belt by the crystallisation of igneous rocks at c. 3000–2900 Ma, including rhyolites that are well preserved. This event is not recorded in the northern part of the belt and may represent southward growth away from a cratonic core at this time. The orthogneisses across the entire belt were subsequently affected by a metamorphic event at c. 2730–2660 Ma, which included intrusions of granites and northward cratonic growth. A few samples also yield evidence of a younger Paleoproterozoic overprint associated with the formation of the 1.90–1.80 Ga Rinkian Belt. The Archean basement rocks of the Rinkian Belt have previously been correlated with similar rocks exposed in northeast Canada and, consequently, they have been referred to as the Greenland part of the Rae craton. The new data support this correlation in general but reveal that Greenland contains the oldest rocks of the Rae craton discovered so far. The new data also show that the Rinkian Belt has a significantly different Archean history than the basement underlying the Nagssugtoqidian orogen to the south. This supports former models that envision two separate Archean cratons colliding during the Paleoproterozoic and that a suture of this age is situated in the central Disko Bugt area.