Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield
The ratios of refractory element such as Nb/Ta and Zr/Hf (17,5-19.9 and 34.3-36, respectively [1,2]), in the unfractionated and in the silicate Earth are assumed to follow those of the chondrites. However, the Earth’s crust and other major silicate reservoirs show subchondritic Nb/Ta values (~12-15....
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European Association of Geochemistry
2019
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ftunivturku:oai:www.utupub.fi:10024/172935 2023-05-15T16:12:55+02:00 Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield Kara Jaakko Väisänen Markku geologia, Geology 2606902 2019-08-18T00:00:00 https://www.utupub.fi/handle/10024/172935 https://goldschmidtabstracts.info/2019/1610.pdf unknown European Association of Geochemistry Goldschmidt Abstracts, 2019 Goldschmidt2019 https://www.utupub.fi/handle/10024/172935 https://goldschmidtabstracts.info/2019/1610.pdf URN:NBN:fi-fe2021042827688 2019 ftunivturku 2022-11-03T00:03:03Z The ratios of refractory element such as Nb/Ta and Zr/Hf (17,5-19.9 and 34.3-36, respectively [1,2]), in the unfractionated and in the silicate Earth are assumed to follow those of the chondrites. However, the Earth’s crust and other major silicate reservoirs show subchondritic Nb/Ta values (~12-15.5) suggesting a mass imbalance for Nb and Ta in Earth which have led to so-called “Nb-Ta paradox” and searching for a suprachondritic Nb/Ta reservoir and “missing Nb” [3]. During its formation Earth’s core might have fractionated Nb making it a potential reservoir for Nb [4]. The Nb/Ta fractionation, however, is an ongoing process during continent formation so other reservoirs such as refractory rutile-bearing eclogites [2], subcontinental lithospheric mantle [5] or rutile-bearing deep arc cumulates [6] could explain part of the HFSE mass inbalance. We have studied Nb, Ta, Zr and Hf concentrations of 1.86 Ga monzogabbros from southwestern Finland. The rocks show elevated Nb/Ta (~16-38) and Zr/Hf (~ 41-48) ratios and OIB-like enriched geochemical features with low initial zircon ε Hf values but high ε Nd values. This is in contrast to the older 1.90-1.88 Ga magmatism within the same area [7]. Our results suggest a residence of a high Nb/Ta and Zr/Hf reservoir under the central Fennoscandian shield during the Paleoproterozoic and a link between the voluminous 1.90-1.88 Ga synorogenic magmatism with low Nb/Ta ratios and elevated Nb/Ta and Zr/Hf ratios in the 1.86 Ga gabbroic magmatism. Other/Unknown Material Fennoscandian University of Turku: UTUPub |
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University of Turku: UTUPub |
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The ratios of refractory element such as Nb/Ta and Zr/Hf (17,5-19.9 and 34.3-36, respectively [1,2]), in the unfractionated and in the silicate Earth are assumed to follow those of the chondrites. However, the Earth’s crust and other major silicate reservoirs show subchondritic Nb/Ta values (~12-15.5) suggesting a mass imbalance for Nb and Ta in Earth which have led to so-called “Nb-Ta paradox” and searching for a suprachondritic Nb/Ta reservoir and “missing Nb” [3]. During its formation Earth’s core might have fractionated Nb making it a potential reservoir for Nb [4]. The Nb/Ta fractionation, however, is an ongoing process during continent formation so other reservoirs such as refractory rutile-bearing eclogites [2], subcontinental lithospheric mantle [5] or rutile-bearing deep arc cumulates [6] could explain part of the HFSE mass inbalance. We have studied Nb, Ta, Zr and Hf concentrations of 1.86 Ga monzogabbros from southwestern Finland. The rocks show elevated Nb/Ta (~16-38) and Zr/Hf (~ 41-48) ratios and OIB-like enriched geochemical features with low initial zircon ε Hf values but high ε Nd values. This is in contrast to the older 1.90-1.88 Ga magmatism within the same area [7]. Our results suggest a residence of a high Nb/Ta and Zr/Hf reservoir under the central Fennoscandian shield during the Paleoproterozoic and a link between the voluminous 1.90-1.88 Ga synorogenic magmatism with low Nb/Ta ratios and elevated Nb/Ta and Zr/Hf ratios in the 1.86 Ga gabbroic magmatism. |
author2 |
geologia, Geology 2606902 |
author |
Kara Jaakko Väisänen Markku |
spellingShingle |
Kara Jaakko Väisänen Markku Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield |
author_facet |
Kara Jaakko Väisänen Markku |
author_sort |
Kara Jaakko |
title |
Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield |
title_short |
Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield |
title_full |
Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield |
title_fullStr |
Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield |
title_full_unstemmed |
Source for suprachondritic Nb/Ta and Zr/Hf values in 1.86 Ga monzogabbros in south-central Fennoscandian Shield |
title_sort |
source for suprachondritic nb/ta and zr/hf values in 1.86 ga monzogabbros in south-central fennoscandian shield |
publisher |
European Association of Geochemistry |
publishDate |
2019 |
url |
https://www.utupub.fi/handle/10024/172935 https://goldschmidtabstracts.info/2019/1610.pdf |
genre |
Fennoscandian |
genre_facet |
Fennoscandian |
op_relation |
Goldschmidt Abstracts, 2019 Goldschmidt2019 https://www.utupub.fi/handle/10024/172935 https://goldschmidtabstracts.info/2019/1610.pdf URN:NBN:fi-fe2021042827688 |
_version_ |
1765998518809395200 |