Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland
Sm-Nd data on rock suites from early Archaean provinces in northern Canada and West Greenland clearly demonstrate that tectonothermal (i.e. igneous, metamorphic, tectonic) processes which affected the rocks long after their formation produced open-system behaviour leading to effective resetting of t...
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ftqueensland:oai:eprints.qut.edu.au:126207 2024-02-11T10:03:33+01:00 Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland Moorbath, S. Whitehouse, M. J. Kamber, B. S. 1997 https://eprints.qut.edu.au/126207/ unknown Elsevier doi:10.1016/s0009-2541(96)00117-9 Moorbath, S., Whitehouse, M. J., & Kamber, B. S. (1997) Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland. Chemical Geology, 135(3-4), pp. 213-231. https://eprints.qut.edu.au/126207/ Science & Engineering Faculty Consult author(s) regarding copyright matters This work is covered by copyright. Unless the document is being made available under a Creative Commons Licence, you must assume that re-use is limited to personal use and that permission from the copyright owner must be obtained for all other uses. If the document is available under a Creative Commons License (or other specified license) then refer to the Licence for details of permitted re-use. It is a condition of access that users recognise and abide by the legal requirements associated with these rights. If you believe that this work infringes copyright please provide details by email to qut.copyright@qut.edu.au Chemical Geology Archaean mantle crust Nd isotopes geochronology isua supracrustal belt early archean crust sm-nd amitsoq gneisses whole-rock isukasia area enderby land rb-sr age metamorphism Geochemistry & Geophysics Contribution to Journal 1997 ftqueensland https://doi.org/10.1016/s0009-2541(96)00117-9 2024-01-15T23:22:31Z Sm-Nd data on rock suites from early Archaean provinces in northern Canada and West Greenland clearly demonstrate that tectonothermal (i.e. igneous, metamorphic, tectonic) processes which affected the rocks long after their formation produced open-system behaviour leading to effective resetting of the Sm-Nd system accompanied by complete, or near-complete, Nd-isotope homogenisation. This means that extreme caution is required in interpreting highly variable initial epsilon(Nd) values of ancient rocks in terms of long-standing regional mantle heterogeneity or of complex mantle-crust interaction processes. In particular, calculated initial epsilon(Nd), values based on high-precision zircon U-Pb dates may be of little or no significance in terms of geochemical evolution of early mantle and crust source regions. A striking example is provided by the Acasta gneisses of northern Canada, with published SHRIMP U-Pb zircon dates in the range 3.6-4.0 Ga and apparent, initial epsilon(Nd) values in the range -4.8 to +3.6 (Bowring and Housh, 1995). A combination of 34 published and new Sm-Nd whole-rock analyses for a wide range of rock types yields a regression (errorchron) age of 3371 +/- 59 Ma (MSWD = 9.2), with initial epsilon(Nd) = -5.6 +/- 0.7. Whilst the very negative initial epsilon(Nd) provides strong, independent support for the extreme age of the Acasta gneiss protolith, resetting of the Sm-Nd system at similar to 3.4 Ga renders calculation of initial epsilon(Nd) based on the zircon U-Pb dates geologically meaningless. Analogous considerations for early Archaean Akilia enclaves and host Amitsoq gneisses of West Greenland suggest that their published range of initial epsilon(Nd) values of similar to -4.5 to +4.5 at similar to 3.73-3.87 Ca (Bennett et al., 1993) may be unrealistically wide and, therefore, inappropriate for modelling upper-mantle heterogeneity. In an attempt to determine a realistic initial epsilon(Nd) value, we have regressed 58 published and new Sm-Nd data for two major rock units of the Isua ... Article in Journal/Newspaper Enderby Land Greenland Queensland University of Technology: QUT ePrints Canada Greenland Chemical Geology 135 3-4 213 231 |
institution |
Open Polar |
collection |
Queensland University of Technology: QUT ePrints |
op_collection_id |
ftqueensland |
language |
unknown |
topic |
Archaean mantle crust Nd isotopes geochronology isua supracrustal belt early archean crust sm-nd amitsoq gneisses whole-rock isukasia area enderby land rb-sr age metamorphism Geochemistry & Geophysics |
spellingShingle |
Archaean mantle crust Nd isotopes geochronology isua supracrustal belt early archean crust sm-nd amitsoq gneisses whole-rock isukasia area enderby land rb-sr age metamorphism Geochemistry & Geophysics Moorbath, S. Whitehouse, M. J. Kamber, B. S. Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland |
topic_facet |
Archaean mantle crust Nd isotopes geochronology isua supracrustal belt early archean crust sm-nd amitsoq gneisses whole-rock isukasia area enderby land rb-sr age metamorphism Geochemistry & Geophysics |
description |
Sm-Nd data on rock suites from early Archaean provinces in northern Canada and West Greenland clearly demonstrate that tectonothermal (i.e. igneous, metamorphic, tectonic) processes which affected the rocks long after their formation produced open-system behaviour leading to effective resetting of the Sm-Nd system accompanied by complete, or near-complete, Nd-isotope homogenisation. This means that extreme caution is required in interpreting highly variable initial epsilon(Nd) values of ancient rocks in terms of long-standing regional mantle heterogeneity or of complex mantle-crust interaction processes. In particular, calculated initial epsilon(Nd), values based on high-precision zircon U-Pb dates may be of little or no significance in terms of geochemical evolution of early mantle and crust source regions. A striking example is provided by the Acasta gneisses of northern Canada, with published SHRIMP U-Pb zircon dates in the range 3.6-4.0 Ga and apparent, initial epsilon(Nd) values in the range -4.8 to +3.6 (Bowring and Housh, 1995). A combination of 34 published and new Sm-Nd whole-rock analyses for a wide range of rock types yields a regression (errorchron) age of 3371 +/- 59 Ma (MSWD = 9.2), with initial epsilon(Nd) = -5.6 +/- 0.7. Whilst the very negative initial epsilon(Nd) provides strong, independent support for the extreme age of the Acasta gneiss protolith, resetting of the Sm-Nd system at similar to 3.4 Ga renders calculation of initial epsilon(Nd) based on the zircon U-Pb dates geologically meaningless. Analogous considerations for early Archaean Akilia enclaves and host Amitsoq gneisses of West Greenland suggest that their published range of initial epsilon(Nd) values of similar to -4.5 to +4.5 at similar to 3.73-3.87 Ca (Bennett et al., 1993) may be unrealistically wide and, therefore, inappropriate for modelling upper-mantle heterogeneity. In an attempt to determine a realistic initial epsilon(Nd) value, we have regressed 58 published and new Sm-Nd data for two major rock units of the Isua ... |
format |
Article in Journal/Newspaper |
author |
Moorbath, S. Whitehouse, M. J. Kamber, B. S. |
author_facet |
Moorbath, S. Whitehouse, M. J. Kamber, B. S. |
author_sort |
Moorbath, S. |
title |
Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland |
title_short |
Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland |
title_full |
Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland |
title_fullStr |
Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland |
title_full_unstemmed |
Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland |
title_sort |
extreme nd-isotope heterogeneity in the early archaean - fact or fiction? case histories from northern canada and west greenland |
publisher |
Elsevier |
publishDate |
1997 |
url |
https://eprints.qut.edu.au/126207/ |
geographic |
Canada Greenland |
geographic_facet |
Canada Greenland |
genre |
Enderby Land Greenland |
genre_facet |
Enderby Land Greenland |
op_source |
Chemical Geology |
op_relation |
doi:10.1016/s0009-2541(96)00117-9 Moorbath, S., Whitehouse, M. J., & Kamber, B. S. (1997) Extreme Nd-isotope heterogeneity in the early Archaean - Fact or fiction? Case histories from northern Canada and West Greenland. Chemical Geology, 135(3-4), pp. 213-231. https://eprints.qut.edu.au/126207/ Science & Engineering Faculty |
op_rights |
Consult author(s) regarding copyright matters This work is covered by copyright. Unless the document is being made available under a Creative Commons Licence, you must assume that re-use is limited to personal use and that permission from the copyright owner must be obtained for all other uses. If the document is available under a Creative Commons License (or other specified license) then refer to the Licence for details of permitted re-use. It is a condition of access that users recognise and abide by the legal requirements associated with these rights. If you believe that this work infringes copyright please provide details by email to qut.copyright@qut.edu.au |
op_doi |
https://doi.org/10.1016/s0009-2541(96)00117-9 |
container_title |
Chemical Geology |
container_volume |
135 |
container_issue |
3-4 |
container_start_page |
213 |
op_container_end_page |
231 |
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1790599818647699456 |