Mesoproterozoic dykes in the Timmiarmiit area, Southeast Greenland: evidence for a continuous Gardar dyke swarm across Greenland’s North Atlantic Craton

During the Proterozoic, several mafic dykes with variable trends and mineralogies intruded the Archaean basement of Southeast Greenland. Some of the younger ENE-trending dykes are interpreted to represent a prolongation of the Mesoproterozoic Gardar Province, and have been termed Timmiarmiit dykes. Extrapolations of their trends across the inland ice sheet coincide with the northernmost so-called brown dykes (BD’s) which are part of the Gardar Province. Baddeleyite U–Pb ID-TIMS analyses for three ENE-trending Timmiarmiit dykes give ages of 1277 ± 4, 1275 ± 3 and 1268 ± 4 Ma, which are slightly younger than the oldest (BD₀ = 1284–1279 ± 3 Ma, Upton 2013) and only dated generation of dykes in the Gardar Province, and thereby indirectly provide a possible age for the two younger dyke generations (BD₁ and BD₂). The Timmiarmiit–Gardar correlation is strengthened by a rigorous multivariate statistical analysis, on the basis of all major and trace elements. Thus, a coherent ENE-trending trans-Greenlandic dyke swarm is constituted. The major and trace element data of the Timmiarmiit dykes show that they crystallised from comparably evolved mantle-derived magma with minor crustal contamination and indicate a strong contribution of a metasomatised subcontinental lithospheric mantle component in the evolution of melts. This component was probably influenced by supra-subduction zone metasomatism during the Palaeoproterozoic Ketilidian orogeny. The data presented here, in addition to recent plate reconstruction models, give new evidence for a petrogenetic link between rift-related Mesoproterozoic magmatism in North America, South Greenland and Central Scandinavia which possibly formed in response to back-arc basin formation.