Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite
Excesses of 230Th over 238U in mid-ocean ridge basalts (MORB) require that the mantle source region preferentially retains U over Th during partial melting. Based on existing mineral-melt partitioning data, 230Th excesses are widely cited as evidence that partial melting beneath ridges begins within...
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2016
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Online Access: | https://doi.org/10.1016/S0009-2541(99)00127-8 https://ora.ox.ac.uk/objects/uuid:764cc3a2-ac56-4336-8aec-906f5b038aa2 |
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ftuloxford:oai:ora.ox.ac.uk:uuid:764cc3a2-ac56-4336-8aec-906f5b038aa2 2023-05-15T13:41:28+02:00 Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite Turner, S Blundy, J Wood, B Hole, M 2016-07-28 https://doi.org/10.1016/S0009-2541(99)00127-8 https://ora.ox.ac.uk/objects/uuid:764cc3a2-ac56-4336-8aec-906f5b038aa2 eng eng doi:10.1016/S0009-2541(99)00127-8 https://ora.ox.ac.uk/objects/uuid:764cc3a2-ac56-4336-8aec-906f5b038aa2 https://doi.org/10.1016/S0009-2541(99)00127-8 info:eu-repo/semantics/embargoedAccess Journal article 2016 ftuloxford https://doi.org/10.1016/S0009-2541(99)00127-8 2022-06-28T20:15:44Z Excesses of 230Th over 238U in mid-ocean ridge basalts (MORB) require that the mantle source region preferentially retains U over Th during partial melting. Based on existing mineral-melt partitioning data, 230Th excesses are widely cited as evidence that partial melting beneath ridges begins within the garnet stability field, at pressures over 2.8 GPa. However, recent experimental and theoretical studies of U-Th partitioning show that melting in the presence of aluminous mantle clinopyroxene may also generate 230Th-excess. In order to try to distinguish between these models we sought basalts with independent constraints on their depth and extent of partial melting. We report data from alkali basalts from the Antarctic Peninsula whose tectonic setting indicates that they formed by < 6% partial melting at pressures of < 2 GPa, well within the spinel stability field. Their major and trace element chemistry is best modelled by ~ 4% partial melting at pressures of 1-2 GPa, in excellent agreement with that inferred from the plate structure. However, these rocks preserve large (6-26%) 230Th-excesses, which would conventionally be ascribed to the involvement of garnet. Instead we show that the trace element signature and isotopic data can be reconciled with partial melting involving residual aluminous-clinopyroxene within the spinel stability field. These Antarctic Peninsula basalts provide the first observational evidence that significant 230Th-excesses can be produced by partial melting of spinel lherzolite and challenge the perceived importance of garnet in MORB petrogenesis. Article in Journal/Newspaper Antarc* Antarctic Antarctic Peninsula ORA - Oxford University Research Archive Antarctic Antarctic Peninsula The Antarctic Chemical Geology 162 2 127 136 |
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Open Polar |
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ORA - Oxford University Research Archive |
op_collection_id |
ftuloxford |
language |
English |
description |
Excesses of 230Th over 238U in mid-ocean ridge basalts (MORB) require that the mantle source region preferentially retains U over Th during partial melting. Based on existing mineral-melt partitioning data, 230Th excesses are widely cited as evidence that partial melting beneath ridges begins within the garnet stability field, at pressures over 2.8 GPa. However, recent experimental and theoretical studies of U-Th partitioning show that melting in the presence of aluminous mantle clinopyroxene may also generate 230Th-excess. In order to try to distinguish between these models we sought basalts with independent constraints on their depth and extent of partial melting. We report data from alkali basalts from the Antarctic Peninsula whose tectonic setting indicates that they formed by < 6% partial melting at pressures of < 2 GPa, well within the spinel stability field. Their major and trace element chemistry is best modelled by ~ 4% partial melting at pressures of 1-2 GPa, in excellent agreement with that inferred from the plate structure. However, these rocks preserve large (6-26%) 230Th-excesses, which would conventionally be ascribed to the involvement of garnet. Instead we show that the trace element signature and isotopic data can be reconciled with partial melting involving residual aluminous-clinopyroxene within the spinel stability field. These Antarctic Peninsula basalts provide the first observational evidence that significant 230Th-excesses can be produced by partial melting of spinel lherzolite and challenge the perceived importance of garnet in MORB petrogenesis. |
format |
Article in Journal/Newspaper |
author |
Turner, S Blundy, J Wood, B Hole, M |
spellingShingle |
Turner, S Blundy, J Wood, B Hole, M Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite |
author_facet |
Turner, S Blundy, J Wood, B Hole, M |
author_sort |
Turner, S |
title |
Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite |
title_short |
Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite |
title_full |
Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite |
title_fullStr |
Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite |
title_full_unstemmed |
Large Th-230-excesses in basalts produced by partial melting of spinel lherzolite |
title_sort |
large th-230-excesses in basalts produced by partial melting of spinel lherzolite |
publishDate |
2016 |
url |
https://doi.org/10.1016/S0009-2541(99)00127-8 https://ora.ox.ac.uk/objects/uuid:764cc3a2-ac56-4336-8aec-906f5b038aa2 |
geographic |
Antarctic Antarctic Peninsula The Antarctic |
geographic_facet |
Antarctic Antarctic Peninsula The Antarctic |
genre |
Antarc* Antarctic Antarctic Peninsula |
genre_facet |
Antarc* Antarctic Antarctic Peninsula |
op_relation |
doi:10.1016/S0009-2541(99)00127-8 https://ora.ox.ac.uk/objects/uuid:764cc3a2-ac56-4336-8aec-906f5b038aa2 https://doi.org/10.1016/S0009-2541(99)00127-8 |
op_rights |
info:eu-repo/semantics/embargoedAccess |
op_doi |
https://doi.org/10.1016/S0009-2541(99)00127-8 |
container_title |
Chemical Geology |
container_volume |
162 |
container_issue |
2 |
container_start_page |
127 |
op_container_end_page |
136 |
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1766151070142169088 |