A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation
New high-precision niobium (Nb) and tantalum (Ta) concentration data are presented for early Archaean metabasalts, metabasaltic komatiites and their erosion products (mafic metapelites) from SW Greenland and the Acasta gneiss complex, Canada. Individual datasets consistently show sub-chondritic Nb/T...
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ftqueensland:oai:eprints.qut.edu.au:126317 2024-05-19T07:41:21+00:00 A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation Kamber, B. S. Greig, A. Schoenberg, R. Collerson, K. D. 2003 https://eprints.qut.edu.au/126317/ unknown Elsevier doi:10.1016/s0301-9268(03)00100-1 Kamber, B. S., Greig, A., Schoenberg, R., & Collerson, K. D. (2003) A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation. Precambrian Research, 126(3-4), pp. 289-308. https://eprints.qut.edu.au/126317/ Science & Engineering Faculty; Australian Research Centre for Aerospace Automation 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 Precambrian Research earth niobium tantalum abitibi greenstone-belt trace-element systematics nd-isotope heterogeneity southern west greenland plume-arc interaction superior province geological samples northwest-territories lithospheric mantle supracrustal belt Geology Contribution to Journal 2003 ftqueensland https://doi.org/10.1016/s0301-9268(03)00100-1 2024-04-30T23:47:21Z New high-precision niobium (Nb) and tantalum (Ta) concentration data are presented for early Archaean metabasalts, metabasaltic komatiites and their erosion products (mafic metapelites) from SW Greenland and the Acasta gneiss complex, Canada. Individual datasets consistently show sub-chondritic Nb/Ta ratios averaging 15.1+/-11.6. This finding is discussed with regard to two competing models for the solution of the Nb-deficit that characterises the accessible Earth. Firstly, we test whether Nb could have sequestered into the core due to its slightly siderophile (or chalcophile) character under very reducing conditions, as recently proposed from experimental evidence. We demonstrate that troilite inclusions of the Canyon Diablo iron meteorite have Nb and V concentrations in excess of typical chondrites but that the metal phase of the Grant, Toluca and Canyon Diablo iron meteorites do not have significant concentrations of these lithophile elements. We find that if the entire accessible Earth Nb-deficit were explained by Nb in the core, only ca. 17% of the mantle could be depleted and that by 3.7 Ga, continental crust would have already achieved ca. 50% of its present mass. Nb/Ta systematics of late Archaean metabasalts compiled from the literature would further require that by 2.5 Ga, 90% of the present mass of continental crust was already in existence. As an alternative to this explanation, we propose that the average Nb/Ta ratio (15.1+/-11.6) of Earth's oldest mafic rocks is a valid approximation for bulk silicate Earth. This would require that ca. 13% of the terrestrial Nb resided in the Ta-free core. Since the partitioning of Nb between silicate and metal melts depends largely on oxygen fugacity and pressure, this finding could mean that metal/silicate segregation did not occur at the base of a deep magma ocean or that the early mantle was slightly less reducing than generally assumed. A bulk silicate Earth Nb/Ta ratio of 15.1 allows for depletion of up to 40% of the total mantle. This could indicate that in ... Article in Journal/Newspaper Greenland Northwest Territories Queensland University of Technology: QUT ePrints Precambrian Research 126 3-4 289 308 |
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Open Polar |
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Queensland University of Technology: QUT ePrints |
op_collection_id |
ftqueensland |
language |
unknown |
topic |
earth niobium tantalum abitibi greenstone-belt trace-element systematics nd-isotope heterogeneity southern west greenland plume-arc interaction superior province geological samples northwest-territories lithospheric mantle supracrustal belt Geology |
spellingShingle |
earth niobium tantalum abitibi greenstone-belt trace-element systematics nd-isotope heterogeneity southern west greenland plume-arc interaction superior province geological samples northwest-territories lithospheric mantle supracrustal belt Geology Kamber, B. S. Greig, A. Schoenberg, R. Collerson, K. D. A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
topic_facet |
earth niobium tantalum abitibi greenstone-belt trace-element systematics nd-isotope heterogeneity southern west greenland plume-arc interaction superior province geological samples northwest-territories lithospheric mantle supracrustal belt Geology |
description |
New high-precision niobium (Nb) and tantalum (Ta) concentration data are presented for early Archaean metabasalts, metabasaltic komatiites and their erosion products (mafic metapelites) from SW Greenland and the Acasta gneiss complex, Canada. Individual datasets consistently show sub-chondritic Nb/Ta ratios averaging 15.1+/-11.6. This finding is discussed with regard to two competing models for the solution of the Nb-deficit that characterises the accessible Earth. Firstly, we test whether Nb could have sequestered into the core due to its slightly siderophile (or chalcophile) character under very reducing conditions, as recently proposed from experimental evidence. We demonstrate that troilite inclusions of the Canyon Diablo iron meteorite have Nb and V concentrations in excess of typical chondrites but that the metal phase of the Grant, Toluca and Canyon Diablo iron meteorites do not have significant concentrations of these lithophile elements. We find that if the entire accessible Earth Nb-deficit were explained by Nb in the core, only ca. 17% of the mantle could be depleted and that by 3.7 Ga, continental crust would have already achieved ca. 50% of its present mass. Nb/Ta systematics of late Archaean metabasalts compiled from the literature would further require that by 2.5 Ga, 90% of the present mass of continental crust was already in existence. As an alternative to this explanation, we propose that the average Nb/Ta ratio (15.1+/-11.6) of Earth's oldest mafic rocks is a valid approximation for bulk silicate Earth. This would require that ca. 13% of the terrestrial Nb resided in the Ta-free core. Since the partitioning of Nb between silicate and metal melts depends largely on oxygen fugacity and pressure, this finding could mean that metal/silicate segregation did not occur at the base of a deep magma ocean or that the early mantle was slightly less reducing than generally assumed. A bulk silicate Earth Nb/Ta ratio of 15.1 allows for depletion of up to 40% of the total mantle. This could indicate that in ... |
format |
Article in Journal/Newspaper |
author |
Kamber, B. S. Greig, A. Schoenberg, R. Collerson, K. D. |
author_facet |
Kamber, B. S. Greig, A. Schoenberg, R. Collerson, K. D. |
author_sort |
Kamber, B. S. |
title |
A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
title_short |
A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
title_full |
A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
title_fullStr |
A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
title_full_unstemmed |
A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
title_sort |
refined solution to earth's hidden niobium: implications for evolution of continental crust and mode of core formation |
publisher |
Elsevier |
publishDate |
2003 |
url |
https://eprints.qut.edu.au/126317/ |
genre |
Greenland Northwest Territories |
genre_facet |
Greenland Northwest Territories |
op_source |
Precambrian Research |
op_relation |
doi:10.1016/s0301-9268(03)00100-1 Kamber, B. S., Greig, A., Schoenberg, R., & Collerson, K. D. (2003) A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation. Precambrian Research, 126(3-4), pp. 289-308. https://eprints.qut.edu.au/126317/ Science & Engineering Faculty; Australian Research Centre for Aerospace Automation |
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/s0301-9268(03)00100-1 |
container_title |
Precambrian Research |
container_volume |
126 |
container_issue |
3-4 |
container_start_page |
289 |
op_container_end_page |
308 |
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1799480949215330304 |