238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean
Phonolite pumice found floating offshore of Tristan da Cunha following intense seismic activity southeast of the island July 29–30, 2004 was analyzed for 238U- and 232Th-series nuclides to determine initial 230Th, 226Ra, 210Pb, 210Po, 228Ra, and 228Th activities. The initial (210Po/210Pb) value of 0...
Published in: | Geochimica et Cosmochimica Acta |
---|---|
Main Authors: | , , , , |
Format: | Article in Journal/Newspaper |
Language: | unknown |
Published: |
Elsevier
2008
|
Subjects: | |
Online Access: | http://nora.nerc.ac.uk/id/eprint/4855/ http://www.sciencedirect.com/science/journal/00167037 |
id |
ftnerc:oai:nora.nerc.ac.uk:4855 |
---|---|
record_format |
openpolar |
spelling |
ftnerc:oai:nora.nerc.ac.uk:4855 2024-06-09T07:49:34+00:00 238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean Reagan, M.K. Turner, S. Legg, M. Simms, K.W.W. Hards, Vicky 2008 http://nora.nerc.ac.uk/id/eprint/4855/ http://www.sciencedirect.com/science/journal/00167037 unknown Elsevier Reagan, M.K.; Turner, S.; Legg, M.; Simms, K.W.W.; Hards, Vicky. 2008 238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean. Geochimica et Cosmochimica Acta, 72 (17). 4367-4378. https://doi.org/10.1016/j.gca.2008.06.002 <https://doi.org/10.1016/j.gca.2008.06.002> Earth Sciences Publication - Article PeerReviewed 2008 ftnerc https://doi.org/10.1016/j.gca.2008.06.002 2024-05-15T08:49:44Z Phonolite pumice found floating offshore of Tristan da Cunha following intense seismic activity southeast of the island July 29–30, 2004 was analyzed for 238U- and 232Th-series nuclides to determine initial 230Th, 226Ra, 210Pb, 210Po, 228Ra, and 228Th activities. The initial (210Po/210Pb) value of 0.15 for the phonolite shows that, like most subaerial lavas, this subaqueous tephra degassed most of its 210Po upon eruption. The (230Th/232Th) and (238U/232Th) values for the phonolite are similar to those of the trachyandesites erupted in 1961 from Tristan da Cunha. However, the relative activities of 210Pb, 226Ra, and 230Th in the phonolite contrast with those of the trachyandesites, in that 210Pb and 230Th are both strongly enriched with respect to 226Ra. In addition, the phonolite had a small deficit in 228Ra with respect to 232Th. The Ra deficits likely resulted from partitioning into feldspars and hornblende in a time frame that extended over several decades to a century. These disequilibria can be explained by crystal fractionation at a decreasing rate through time at an average of 3–5 × 10−3 year−1. The calculated crystallization rate is about an order of magnitude faster than has been calculated for most other phonolites and trachytes, and about half that calculated for crystallization of the Makaopuhi lava lake. These data imply that the 2004 magma was not the differentiated cap of a much larger body that remained at depth. Instead, it was likely the residue of a relatively small body of more mafic magma that was injected into the crust southeast Tristan and underwent extensive and rapid crystal fractionation before it erupted. Article in Journal/Newspaper South Atlantic Ocean Natural Environment Research Council: NERC Open Research Archive Lava Lake ENVELOPE(-128.996,-128.996,55.046,55.046) Tristan ENVELOPE(140.900,140.900,-66.735,-66.735) Geochimica et Cosmochimica Acta 72 17 4367 4378 |
institution |
Open Polar |
collection |
Natural Environment Research Council: NERC Open Research Archive |
op_collection_id |
ftnerc |
language |
unknown |
topic |
Earth Sciences |
spellingShingle |
Earth Sciences Reagan, M.K. Turner, S. Legg, M. Simms, K.W.W. Hards, Vicky 238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean |
topic_facet |
Earth Sciences |
description |
Phonolite pumice found floating offshore of Tristan da Cunha following intense seismic activity southeast of the island July 29–30, 2004 was analyzed for 238U- and 232Th-series nuclides to determine initial 230Th, 226Ra, 210Pb, 210Po, 228Ra, and 228Th activities. The initial (210Po/210Pb) value of 0.15 for the phonolite shows that, like most subaerial lavas, this subaqueous tephra degassed most of its 210Po upon eruption. The (230Th/232Th) and (238U/232Th) values for the phonolite are similar to those of the trachyandesites erupted in 1961 from Tristan da Cunha. However, the relative activities of 210Pb, 226Ra, and 230Th in the phonolite contrast with those of the trachyandesites, in that 210Pb and 230Th are both strongly enriched with respect to 226Ra. In addition, the phonolite had a small deficit in 228Ra with respect to 232Th. The Ra deficits likely resulted from partitioning into feldspars and hornblende in a time frame that extended over several decades to a century. These disequilibria can be explained by crystal fractionation at a decreasing rate through time at an average of 3–5 × 10−3 year−1. The calculated crystallization rate is about an order of magnitude faster than has been calculated for most other phonolites and trachytes, and about half that calculated for crystallization of the Makaopuhi lava lake. These data imply that the 2004 magma was not the differentiated cap of a much larger body that remained at depth. Instead, it was likely the residue of a relatively small body of more mafic magma that was injected into the crust southeast Tristan and underwent extensive and rapid crystal fractionation before it erupted. |
format |
Article in Journal/Newspaper |
author |
Reagan, M.K. Turner, S. Legg, M. Simms, K.W.W. Hards, Vicky |
author_facet |
Reagan, M.K. Turner, S. Legg, M. Simms, K.W.W. Hards, Vicky |
author_sort |
Reagan, M.K. |
title |
238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean |
title_short |
238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean |
title_full |
238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean |
title_fullStr |
238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean |
title_full_unstemmed |
238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean |
title_sort |
238u and 232th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near tristan da cunha, south atlantic ocean |
publisher |
Elsevier |
publishDate |
2008 |
url |
http://nora.nerc.ac.uk/id/eprint/4855/ http://www.sciencedirect.com/science/journal/00167037 |
long_lat |
ENVELOPE(-128.996,-128.996,55.046,55.046) ENVELOPE(140.900,140.900,-66.735,-66.735) |
geographic |
Lava Lake Tristan |
geographic_facet |
Lava Lake Tristan |
genre |
South Atlantic Ocean |
genre_facet |
South Atlantic Ocean |
op_relation |
Reagan, M.K.; Turner, S.; Legg, M.; Simms, K.W.W.; Hards, Vicky. 2008 238U and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean. Geochimica et Cosmochimica Acta, 72 (17). 4367-4378. https://doi.org/10.1016/j.gca.2008.06.002 <https://doi.org/10.1016/j.gca.2008.06.002> |
op_doi |
https://doi.org/10.1016/j.gca.2008.06.002 |
container_title |
Geochimica et Cosmochimica Acta |
container_volume |
72 |
container_issue |
17 |
container_start_page |
4367 |
op_container_end_page |
4378 |
_version_ |
1801382252750307328 |