TY - JOUR

T1 - Pressure-Temperature history of the 1.9 Ga Nagssugtoqidian Orogeny in the Tasiilaq Region, South-East Greenland

T2 - Amphibolite facies metamorphism of a Palaeoproterozoic accretionary prism

AU - Crotty, Catherine

AU - van Hinsberg, Vincent

AU - Szilas, Kristoffer

N1 - Funding Information: The presented work is based on fieldwork in 2014 in south-east Greenland, which was organised and led by GEUS and co-financed by GEUS and MMR . The research was funded by an Osisko research stipend and NSERC Discovery Grant (no. RGPIN-418727-2012 ) to VJvH. We thank Majken Djurhuus Poulsen, Lærke L. Thomsen, Diogo Rosa, Annika Dziggel, Sascha Müller, Thomas Kokfelt, Bo Møller Stensgaard and all other participants of the 2014 SEGMENT expedition for help in the field, and a fruitful exchange of ideas on the geological history of the Tasiilaq area. We are grateful for Glenn Poirier and David Diekrup at the University of Ottawa for WDS-EMPA analysis at the Canadian Museum-University of Ottawa Microanalysis laboratory. Funding Information: The presented work is based on fieldwork in 2014 in south-east Greenland, which was organised and led by GEUS and co-financed by GEUS and MMR. The research was funded by an Osisko research stipend and NSERC Discovery Grant (no. RGPIN-418727-2012) to VJvH. We thank Majken Djurhuus Poulsen, Lærke L. Thomsen, Diogo Rosa, Annika Dziggel, Sascha Müller, Thomas Kokfelt, Bo Møller Stensgaard and all other participants of the 2014 SEGMENT expedition for help in the field, and a fruitful exchange of ideas on the geological history of the Tasiilaq area. We are grateful for Glenn Poirier and David Diekrup at the University of Ottawa for WDS-EMPA analysis at the Canadian Museum-University of Ottawa Microanalysis laboratory. Publisher Copyright: © 2022

PY - 2023

Y1 - 2023

N2 - 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 hydrothermal fluids at temperatures of <400 °C resulted in region wide retrogression.

AB - 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 hydrothermal fluids at temperatures of <400 °C resulted in region wide retrogression.

KW - Craton collision

KW - Greenland

KW - Metamorphic history

KW - Palaeoproterozoic

KW - Tasiilaq

U2 - 10.1016/j.lithos.2022.106993

DO - 10.1016/j.lithos.2022.106993

M3 - Journal article

AN - SCOPUS:85144750402

VL - 438-439

JO - Lithos

JF - Lithos

SN - 0024-4937

M1 - 106993

ER -