Pressure-Temperature history of the 1.9 Ga Nagssugtoqidian Orogeny in the Tasiilaq Region, South-East Greenland:Amphibolite facies metamorphism of a Palaeoproterozoic accretionary prism

• Published in: Lithos
• Main Authors: Crotty, Catherine, van Hinsberg, Vincent, Szilas, Kristoffer
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Craton collision; Greenland; Metamorphic history; Palaeoproterozoic; Tasiilaq; Isertoq; Rae; Schweizerland; Ammassalik; Kuummiut; North Atlantic
• Online Access: https://curis.ku.dk/portal/da/publications/pressuretemperature-history-of-the-19-ga-nagssugtoqidian-orogeny-in-the-tasiilaq-region-southeast-greenland(7defd16e-e411-4085-a2cd-6cc97b5fb039).html; https://doi.org/10.1016/j.lithos.2022.106993; https://curis.ku.dk/ws/files/345495795/2023_Crotty_et_al._Lithos_accepted_manuscript.pdf

The Tasiilaq region in SE Greenland records the suturing of two major cratons during the 1.9 Ga Nagssugtoqidian orogeny, with the Rae Craton to the north subducting beneath the North Atlantic Craton (NAC) to the south. Supracrustal rocks that were deposited prior to the orogeny, and record it, can be used to put constraints on the composition and geodynamic relationships between these two cratons. Here, we present a detailed study of the pressure-temperature conditions and metamorphic history of the Kuummiut Terrane (Rae craton) using geothermobarometry and pseudosection modelling and compare it to the adjacent Schweizerland (Rae) and Isertoq terranes (NAC). We show that the supracrustal rocks of the Tasiilaq region record an orogenic pressure temperature path, typical of an accretionary wedge, similar to what is seen in modern orogenies, including the Variscides. The Kuummiut Terrane contains two peak mineral assemblages with distinct peak pressure and temperature at 8.7 to 9.8 kbar at 636 to 680 °C in the west and ∼ 8.2 kbar at ∼735 °C in the east. The suture zone between the Isertoq and Kuummiut terranes was intruded by the Ammassalik Intrusive Complex resulting in the formation of anatectic melts at ∼790 °C and 6.3–8.0 kbar at 1910–1870 Ma, syn- to late- tectonically. This was followed by strike slip, crustal thickening, and regional shearing at 614 to 713 °C and 4.3 kbar to 7.4 kbar. This is the first event to affect all three terranes and juxtaposes blocks with differing peak metamorphism, bringing the Isertoq Supracrustal rocks to the same crustal level as the Kuummiut Supracrustal rocks and thrusting the Schweizerland Terrane on top of the Kuummiut Terrane. The nappe stacking kept upper to mid crustal rocks at close to peak temperatures, resulting in extensive melting, and the formation of pegmatites throughout the region. Post tectonic collapse began as early as 1820 Ma, which marks the end of decompression, with the intrusion of gabbro and granitic complexes at ∼8 km depth. Finally, circulation of ...