New zircon U-Pb geochronology from the Ketilidian orogen of South Greenland

The Paleoproterozoic Ketilidian orogen in South Greenland (1.85-1.73 Ga) is interpreted to be the result of northwards-dipping oblique subduction of an oceanic plate beneath the Archaean continental crust of the North Atlantic Craton. The Ketilidian orogen was part of the subducted-related magmatism and accretionary orogenic belt named the Great Paleoproterozoic Accretionary Orogen that existed along an active margin stretching through Laurentia (North America and South Greenland) to Baltica (Northeast Europe), which formed the supercontinent Columbia/Nuna. Thus, the orogeny represents part of an important episode of crustal growth and preservation in Earth’s history. The Central Domain of the orogeny is dominated by the plutonic remnants of a magmatic arc (the Julianehåb Igneous Complex (JIC), ca. 1.85-1.80 Ga), which eventually grew sufficiently large and stable to subsequently uplift and unroof, to produce rocks interpreted to represent erosional fore-arc deposits that are preserved to the south in the Southern Domain. Between ca. 1.80 Ga and 1.76 Ga, the fore-arc was subjected to metamorphism of amphibolite to granulite facies, and was subsequently intruded by post-tectonic granites (including rapakivi variants) of the Ilua Suite (1.75-1.73 Ga). We present new zircon U-Pb SIMS ages for granitic and metasedimentary rocks sampled at a regional scale in a traverse stretching NW to SW through the Central and Southern Domains of the Ketilidian Orogen in South Greenland. Previous studies have distinguished two pulses of magmatism in the JIC, an early event at ca. 1.85-1.83 Ga and a later phase at ca. 1.80-1.78 Ga. Our JIC samples are dominated by the late stage (<1.83 Ga) with most ages concentrated at 1.8 Ga, suggesting that the main volume of crust in the western portion of the arc was generated over a relatively short period. Ages for the Ilua Suite agree well with previous studies. Zircon age distributions in the metasedimentary rocks of the Southern Domain are consist with detritus dominantly sourced from the JIC, however the presence of small populations of older zircons (up to 2.8 Ga) not observed as inherited zircons in the JIC, indicates that older crustal components also eroded into the fore-arc. These U-Pb zircon results are part of an ongoing larger investigation combining O-Hf isotope compositions in zircon, coupled with whole rock geochemical and isotope data. This research will provide the first thorough geochemical and petrogenetic investigation of the timing, across arc variations, and source components involved in the formation and evolution of South Greenland as well as its contribution in one of the worldwide peaks of continental crustal growth.