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 (BD 0 = 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 (BD 1 and BD 2). 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.
- Programområde 4: Mineralske råstoffer