Geological processes defining the formation of plumasite-type corundum in the Paleoproterozoic Isertoq Terrane, South-East Greenland
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Plumasite-type corundum occurrences in the Nattivit area in South-East Greenland offer a unique opportunity to study corundum formation in-situ where pegmatites intruded into metamorphosed lherzolite and dunite of the Archean-Paleoproterozoic continental crust. The Nattivit area, located in the Isertoq Terrane of North Atlantic Craton, forms part of the overriding plate during convergence of the Nagssugtoqidian orogen (1910-1840 Ma). New field observations and elemental and isotopic geochemical analysis provide further insights in the history of crustal convergence, its exhumation and how corundum was formed. The continental crust in the area consists of metamorphosed mafic to ultramafic rocks and tonalite-trondhjemite-granodiorite (TTG) gneisses, where the mafic rocks in the Isertoq Terrane yield a εNd TDM model age of 3000–2800 Ma. Dunite and lherzolite sills/dikes intruded the mafic rocks before the intrusion of the TTG sheets. The intrusion ages for the TTG obtained from zircon U-Pb geochronology are 2818 ± 8 Ma, 2760 ± 13 Ma to 2667 ± 7 Ma. U-Pb zircon data, zircon textures and Th/U ratios indicate metamorphism occurred at 2698 ± 7 Ma to 2629 ± 11 Ma, 2500–2400 Ma and 1900–1600 Ma. Whole rock geochemical data of mafic to ultramafic rocks show a continental arc affinity, with negative Ta, Nb and positive Pb anomalies. A metasomatic event at 2390 ± 70 Ma partly reset the isotopic signature in the mafic to ultramafic rocks. A marked absence of ages between 2350 and 2100 Ma in the TTG zircon age populations exists, indicating a period with minimal magmatic and/or metamorphic activity. The metamorphic mineral assemblages of the schist, amphibolite, ultramafic rocks and metasomatic reaction zones in ultramafic rocks indicate upper to medium–high amphibolite facies conditions. Kyanite in the metasomatic reaction zones in ultramafic rocks indicate the higher end of the temperature and pressure range above 4.2–10 kbar and 530–800 °C, similar to estimates from dolerite dikes in the Kitak area. The syn-tectonic pegmatites with an intrusion age of 1843 ± 4 Ma formed corundum. The new data indicate that the pegmatite melt/fluid and the geotectonic setting are defining factors for generating plumasite-type corundum.
| Originalsprog | Engelsk |
|---|---|
| Artikelnummer | 106940 |
| Tidsskrift | Precambrian Research |
| Vol/bind | 385 |
| Antal sider | 23 |
| ISSN | 0301-9268 |
| DOI | |
| Status | Udgivet - 2023 |
Bibliografisk note
Funding Information:
This work is part of a PhD project and was supported by the Danish State Fund for Arctic Research and the Geological Survey of Denmark and Greenland (80.15). The authors would like to thank the following people from GEUS: Mojagan Alaei for help with zircon preparation for LA-ICP-MS U-Pb zircon dating, Olga Nielsen for preparation and analysis for major and trace elements, Toke Hvenegaard for sample preparation for geochemical analysis and thin section preparation and Simon Hansen Serre and Maja B. Rasmussen for help with set up to LA-ICP-MS analysis. Thomas F. Kokfelt is thanked for discussion on U-Pb zircon data interpretations and the geology of South-East Greenland. Christina N. Jensen from Department of Geosciences and Natural Resource Management at Copenhagen University is thanked for help with ion chromotographic procedures and preparation for TIMS analysis. We would like to thank Scott Boroughs from the Peter Hooper GeoAnalytical Lab in Washington State University for major element analyses for ultramafic rocks. We would like to thank Vittus Sakæussen, the 2009-winner of the Greenlandic national mineral hunt for guiding us to his corundum locality in 2014. We also thank Dan & Marie Reimer and Hans Christian Florian for boat assistance during field work in the Tasiilaq area in 2014 and 2015.
Funding Information:
This work is part of a PhD project and was supported by the Danish State Fund for Arctic Research and the Geological Survey of Denmark and Greenland (80.15). The authors would like to thank the following people from GEUS: Mojagan Alaei for help with zircon preparation for LA-ICP-MS U-Pb zircon dating, Olga Nielsen for preparation and analysis for major and trace elements, Toke Hvenegaard for sample preparation for geochemical analysis and thin section preparation and Simon Hansen Serre and Maja B. Rasmussen for help with set up to LA-ICP-MS analysis. Thomas F. Kokfelt is thanked for discussion on U-Pb zircon data interpretations and the geology of South-East Greenland. Christina N. Jensen from Department of Geosciences and Natural Resource Management at Copenhagen University is thanked for help with ion chromotographic procedures and preparation for TIMS analysis. We would like to thank Scott Boroughs from the Peter Hooper GeoAnalytical Lab in Washington State University for major element analyses for ultramafic rocks. We would like to thank Vittus Sakæussen, the 2009-winner of the Greenlandic national mineral hunt for guiding us to his corundum locality in 2014. We also thank Dan & Marie Reimer and Hans Christian Florian for boat assistance during field work in the Tasiilaq area in 2014 and 2015.
Publisher Copyright:
© 2022 The Author(s)
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