Break-up related 2170-2120 Ma mafic dykes across the North Atlantic craton: Final dismembering of a North Atlantic-Dharwar craton connection?

摘要

Progress with supercontinental reconstructions relies on accurate age determinations for continental geological units such as mafic dyke swarms. Here we present zircon and baddeleyite U-Pb ID-TIMS isotope data of six mafic dykes from the Archean North Atlantic craton in present-day southern West and South-East Greenland. Two dykes in southern West Greenland yield crystallization ages of 2021 +/- 4 Ma, for the NE-trending Hamborgersund dyke, and 2125 +/- 9 Ma, for the E-trending Angissunguaq dyke. Additional age determinations of mafic dykes from South-East Greenland are 2166 +/- 8 Ma and 2158 +/- 8 Ma for two E W trending dykes, herein named the Skjoldungen dykes, and 2137 +/- 11 and 2124 +/- 11 for two ENE and NE trending dykes, respectively. The name Ruinnwsset dykes is proposed for this slightly younger, ca. 2137-2124 Ma, generation of dykes in SE Greenland, and Nuuk dykes for coeval ca. 2125 Ma dykes in SW Greenland. The Skjoldungen and the Ruinnwsset dykes have primordial mantle geochemical signatures, with only minor LILE-enrichments. These signatures differ from other, more lithospheric', Proterozoic dykes within the region, and may reflect highly attenuated lithospheric extension during their emplacement. Coeval mafic magmatism in North Atlantic and Dharwar cratons suggests that these two fragments coexisted within a common Paleoproterozoic supercraton. A lack of younger age-matches further argue for ca. 2170-2140 Ma rifting and subsequent break-up of this Dharwar-North Atlantic connection, prior to the 2137-2124 Ma emplacement of the Ruinnwsset dykes. Other global age correlations are discussed and a likely paleogeographic reconstruction of North Atlantic craton together with the Dharwar and Superior cratons within a Paleoproterozoic supercraton is presented.