Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland
The Ilímaussaq complex in southern Greenland is a shallow crustal composite intrusion comprising augite syenite, peralkaline granite and volumetrically dominant agpaitic nepheline syenites. Previous studies indicated a baddeleyite U-Pb age of 1160 ± 5 Ma for the augite syenite, the earliest intrusiv...
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Language: | English |
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2019
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Online Access: | https://risweb.st-andrews.ac.uk/portal/en/researchoutput/dating-agpaitic-rocks(c7e521e4-c2ef-4b34-8bfd-d109408e5c63).html https://doi.org/10.1016/j.lithos.2018.10.037 https://research-repository.st-andrews.ac.uk/bitstream/10023/18835/1/Borst_2018_Lithos_Agpaiticrocks_AAM.pdf |
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ftunstandrewcris:oai:risweb.st-andrews.ac.uk:publications/c7e521e4-c2ef-4b34-8bfd-d109408e5c63 2023-05-15T16:28:56+02:00 Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland Borst, A. M. Waight, Tod Finch, A. A. Storey, Michael Le Roux, Petrus 2019-01 application/pdf https://risweb.st-andrews.ac.uk/portal/en/researchoutput/dating-agpaitic-rocks(c7e521e4-c2ef-4b34-8bfd-d109408e5c63).html https://doi.org/10.1016/j.lithos.2018.10.037 https://research-repository.st-andrews.ac.uk/bitstream/10023/18835/1/Borst_2018_Lithos_Agpaiticrocks_AAM.pdf eng eng info:eu-repo/semantics/openAccess Borst , A M , Waight , T , Finch , A A , Storey , M & Le Roux , P 2019 , ' Dating agpaitic rocks : a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland ' , Lithos , vol. 324-325 , pp. 74-88 . https://doi.org/10.1016/j.lithos.2018.10.037 Geochronology Agpaitic nepheline syenites Peralkaline rocks Ilimaussaq Radiogenic isotopes Eudialyte article 2019 ftunstandrewcris https://doi.org/10.1016/j.lithos.2018.10.037 2022-06-02T07:49:27Z The Ilímaussaq complex in southern Greenland is a shallow crustal composite intrusion comprising augite syenite, peralkaline granite and volumetrically dominant agpaitic nepheline syenites. Previous studies indicated a baddeleyite U-Pb age of 1160 ± 5 Ma for the augite syenite, the earliest intrusive unit of the complex. A similar crystallization age, within error, is inferred for the main sequence of agpaitic nepheline syenites. However, direct age determination of these units has been challenging because agpaitic rocks characteristically lack robust phases for in situ U-Pb dating (e.g. zircon/baddeleyite). An additional challenge is the pervasive subsolidus alteration, of which the isotopic effects are poorly constrained. Here we present new U-Pb, Sm-Nd and Rb-Sr isotopic data from whole rocks and mineral separates and a 40 Ar/ 39 Ar amphibole age of three co-genetic agpaitic nepheline syenites (kakortokite) from the lowermost exposed part of the complex. Using a multi-system geochronological approach for mineral separates and whole rocks, we explore the effects of late-stage alteration for each isotopic system. Assuming a closed-system evolution for the hydrothermal fluids (i.e. isotopically similar to the melts) and cooling within a relatively short time-frame (<0.8 Ma), we evaluate whether traditional mineral-whole rock isochron methods can provide useful age constraints for agpaitic rocks. We compare our data with those in the literature, corrected for the most recent decay constants. Single-crystal 40 Ar/ 39 Ar step-heating experiments yield an amphibole plateau age of 1156.6 ± 1.4 Ma (MSWD = 1.5, external error ± 7.7 Ma), which we put forward as the most precise crystallization age for the agpaitic units to date. Kakortokite whole rock and mineral separates (amphibole, eudialyte, feldspar) yield a 206 Pb- 207 Pb isochron age of 1159 ± 17 Ma (MSWD = 0.96) and a 235 U- 207 Pb isochron age of 1168.5 ± 8.8 Ma (MSWD = 0.82). These are within error of the baddeleyite and zircon U-Pb ages from the augite ... Article in Journal/Newspaper Greenland University of St Andrews: Research Portal Greenland Ilimaussaq ENVELOPE(-45.900,-45.900,60.983,60.983) Lithos 324-325 74 88 |
institution |
Open Polar |
collection |
University of St Andrews: Research Portal |
op_collection_id |
ftunstandrewcris |
language |
English |
topic |
Geochronology Agpaitic nepheline syenites Peralkaline rocks Ilimaussaq Radiogenic isotopes Eudialyte |
spellingShingle |
Geochronology Agpaitic nepheline syenites Peralkaline rocks Ilimaussaq Radiogenic isotopes Eudialyte Borst, A. M. Waight, Tod Finch, A. A. Storey, Michael Le Roux, Petrus Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland |
topic_facet |
Geochronology Agpaitic nepheline syenites Peralkaline rocks Ilimaussaq Radiogenic isotopes Eudialyte |
description |
The Ilímaussaq complex in southern Greenland is a shallow crustal composite intrusion comprising augite syenite, peralkaline granite and volumetrically dominant agpaitic nepheline syenites. Previous studies indicated a baddeleyite U-Pb age of 1160 ± 5 Ma for the augite syenite, the earliest intrusive unit of the complex. A similar crystallization age, within error, is inferred for the main sequence of agpaitic nepheline syenites. However, direct age determination of these units has been challenging because agpaitic rocks characteristically lack robust phases for in situ U-Pb dating (e.g. zircon/baddeleyite). An additional challenge is the pervasive subsolidus alteration, of which the isotopic effects are poorly constrained. Here we present new U-Pb, Sm-Nd and Rb-Sr isotopic data from whole rocks and mineral separates and a 40 Ar/ 39 Ar amphibole age of three co-genetic agpaitic nepheline syenites (kakortokite) from the lowermost exposed part of the complex. Using a multi-system geochronological approach for mineral separates and whole rocks, we explore the effects of late-stage alteration for each isotopic system. Assuming a closed-system evolution for the hydrothermal fluids (i.e. isotopically similar to the melts) and cooling within a relatively short time-frame (<0.8 Ma), we evaluate whether traditional mineral-whole rock isochron methods can provide useful age constraints for agpaitic rocks. We compare our data with those in the literature, corrected for the most recent decay constants. Single-crystal 40 Ar/ 39 Ar step-heating experiments yield an amphibole plateau age of 1156.6 ± 1.4 Ma (MSWD = 1.5, external error ± 7.7 Ma), which we put forward as the most precise crystallization age for the agpaitic units to date. Kakortokite whole rock and mineral separates (amphibole, eudialyte, feldspar) yield a 206 Pb- 207 Pb isochron age of 1159 ± 17 Ma (MSWD = 0.96) and a 235 U- 207 Pb isochron age of 1168.5 ± 8.8 Ma (MSWD = 0.82). These are within error of the baddeleyite and zircon U-Pb ages from the augite ... |
format |
Article in Journal/Newspaper |
author |
Borst, A. M. Waight, Tod Finch, A. A. Storey, Michael Le Roux, Petrus |
author_facet |
Borst, A. M. Waight, Tod Finch, A. A. Storey, Michael Le Roux, Petrus |
author_sort |
Borst, A. M. |
title |
Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland |
title_short |
Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland |
title_full |
Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland |
title_fullStr |
Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland |
title_full_unstemmed |
Dating agpaitic rocks:a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland |
title_sort |
dating agpaitic rocks:a multi-system (u/pb, sm/nd, rb/sr and 40 ar/ 39 ar) isotopic study of layered nepheline syenites from the ilímaussaq complex, greenland |
publishDate |
2019 |
url |
https://risweb.st-andrews.ac.uk/portal/en/researchoutput/dating-agpaitic-rocks(c7e521e4-c2ef-4b34-8bfd-d109408e5c63).html https://doi.org/10.1016/j.lithos.2018.10.037 https://research-repository.st-andrews.ac.uk/bitstream/10023/18835/1/Borst_2018_Lithos_Agpaiticrocks_AAM.pdf |
long_lat |
ENVELOPE(-45.900,-45.900,60.983,60.983) |
geographic |
Greenland Ilimaussaq |
geographic_facet |
Greenland Ilimaussaq |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
Borst , A M , Waight , T , Finch , A A , Storey , M & Le Roux , P 2019 , ' Dating agpaitic rocks : a multi-system (U/Pb, Sm/Nd, Rb/Sr and 40 Ar/ 39 Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland ' , Lithos , vol. 324-325 , pp. 74-88 . https://doi.org/10.1016/j.lithos.2018.10.037 |
op_rights |
info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.1016/j.lithos.2018.10.037 |
container_title |
Lithos |
container_volume |
324-325 |
container_start_page |
74 |
op_container_end_page |
88 |
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1766018628012998656 |