TY - JOUR
T1 - The complex tectonic evolution of the craton-adjacent northern margin of the Palaeoproterozoic Ketilidian Orogen, southeastern Greenland
T2 - Evidence from the geochemistry of mafic to intermediate and granitic intrusions
AU - Bagas, Leon
AU - Kolb, Jochen
AU - Nielsen, Troels F.D.
AU - Groves, David I.
N1 - Funding Information:
Greenland Bureau of Minerals and Petroleum (BMP) and the Geological Survey of Denmark and Greenland (GEUS) are gratefully acknowledged for financial support of the field and analytical work. Dr. Allen Nutman, Dr. Gautier Nicoli, Dr. Thomas Ulrich, Dr. Agnete Steenfelt, and an anonymous reviewer are thanked for their reviews of this manuscript. Thomas is also thanked for his participation in fieldwork.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/4
Y1 - 2020/4
N2 - The Archaean Thrym Complex, exposed in southeastern Greenland, is part of the North Atlantic Craton. Its southernmost part is in a transitional zone containing Archaean orthogneiss to the north, and Palaeoproterozoic paragneiss and granitic rocks to the south that are part of the Ketilidian Orogen. This 50 km wide transitional zone includes ca. 2830 Ma orthogneiss that is similar in age to orthogneiss in the central and northern parts of the complex, and ca. 2740 Ma orthogneiss that is synchronous with the ca. 2790–2700 Ma Skjoldungen Orogeny. A significant difference between this zone and the complex to the north is the presence of greenschist-facies sedimentary rocks unconformably overlying orthogneiss and intruded by ca. 1820–1800 Ma granitic and mafic to intermediate intrusions. These intrusions are within the ca. 1854–1799 Ma age-range of the Julianehåb Igneous Complex, with suites, both older and younger than ca. 1830 Ma, that are not restricted to specific zones within the Ketilidian Orogen. The geochemistry of the Palaeoproterozoic mafic to intermediate rocks in the transitional zone shows contamination by orthogneiss from the Thrym Complex, and emplacement within an oceanic-continental transition in a within-plate setting unrelated to subduction. In contrast, the Palaeoproterozoic granites were sourced entirely from Archaean orthogneiss of the Thrym Complex, making them technically I-type granites that have inherited their petrogenetic signature from the orthogneiss. As a result, the Palaeoproterozoic granites and intermediate to mafic igneous rocks have similar chondrite-normalised patterns to the orthogneiss in the Archaean complex. This demonstrates that discrimination diagrams cannot be assumed to be unequivocal for the rocks studied unless the geochemistry of the source rocks is also known.
AB - The Archaean Thrym Complex, exposed in southeastern Greenland, is part of the North Atlantic Craton. Its southernmost part is in a transitional zone containing Archaean orthogneiss to the north, and Palaeoproterozoic paragneiss and granitic rocks to the south that are part of the Ketilidian Orogen. This 50 km wide transitional zone includes ca. 2830 Ma orthogneiss that is similar in age to orthogneiss in the central and northern parts of the complex, and ca. 2740 Ma orthogneiss that is synchronous with the ca. 2790–2700 Ma Skjoldungen Orogeny. A significant difference between this zone and the complex to the north is the presence of greenschist-facies sedimentary rocks unconformably overlying orthogneiss and intruded by ca. 1820–1800 Ma granitic and mafic to intermediate intrusions. These intrusions are within the ca. 1854–1799 Ma age-range of the Julianehåb Igneous Complex, with suites, both older and younger than ca. 1830 Ma, that are not restricted to specific zones within the Ketilidian Orogen. The geochemistry of the Palaeoproterozoic mafic to intermediate rocks in the transitional zone shows contamination by orthogneiss from the Thrym Complex, and emplacement within an oceanic-continental transition in a within-plate setting unrelated to subduction. In contrast, the Palaeoproterozoic granites were sourced entirely from Archaean orthogneiss of the Thrym Complex, making them technically I-type granites that have inherited their petrogenetic signature from the orthogneiss. As a result, the Palaeoproterozoic granites and intermediate to mafic igneous rocks have similar chondrite-normalised patterns to the orthogneiss in the Archaean complex. This demonstrates that discrimination diagrams cannot be assumed to be unequivocal for the rocks studied unless the geochemistry of the source rocks is also known.
KW - Archaean
KW - Greenland
KW - Palaeoproterozoic Ketilidian Orogen
KW - Plate tectonics
KW - Thrym Complex
UR - http://www.scopus.com/inward/record.url?scp=85078715203&partnerID=8YFLogxK
U2 - 10.1016/j.lithos.2020.105384
DO - 10.1016/j.lithos.2020.105384
M3 - Article
AN - SCOPUS:85078715203
SN - 0024-4937
VL - 358-359
JO - Lithos
JF - Lithos
M1 - 105384
ER -