Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii
Late Quaternary, post-shield lavas from the Mauna Kea and Kohala volcanoes on the Big Island of Hawaii have been dated using the 40Ar/39Ar and U–Th/He methods. The objective of the study is to compare the recently demonstrated U–Th/He age method, which uses basaltic olivine phenocrysts, with 40Ar/39...
| Main Authors: | , , , |
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| Format: | Journal Article |
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Pergamon-Elsevier Science Ltd
2010
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| Online Access: | http://hdl.handle.net/20.500.11937/33956 |
| _version_ | 1848754089638232064 |
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| author | Aciego, S. Jourdan, Fred DePaolo, D. Kennedy, B. |
| author_facet | Aciego, S. Jourdan, Fred DePaolo, D. Kennedy, B. |
| author_sort | Aciego, S. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Late Quaternary, post-shield lavas from the Mauna Kea and Kohala volcanoes on the Big Island of Hawaii have been dated using the 40Ar/39Ar and U–Th/He methods. The objective of the study is to compare the recently demonstrated U–Th/He age method, which uses basaltic olivine phenocrysts, with 40Ar/39Ar ages measured on groundmass from the same samples. As a corollary, the age data also increase the precision of the chronology of volcanism on the Big Island. For the U–Th/He ages, U, Th and He concentrations and isotopes were measured to account for U-series disequilibrium and initial He. Single analyses U–Th/He ages for Hamakua lavas from Mauna Kea are 87 ± 40 to 119 ± 23 ka (2σ uncertainties), which are in general equal to or younger than 40Ar/39Ar ages. Basalt from the Polulu sequence on Kohala gives a U–Th/He age of 354 ± 54 ka and a 40Ar/39Ar age of 450 ± 40 ka. All of the U–Th/He ages, and all but one spurious 40Ar/39Ar ages conform to the previously proposed stratigraphy and published 14C and K–Ar ages.The ages also compare favorably to U–Th whole rock–olivine ages calculated from 238U–230Th disequilibria. The U–Th/He and 40Ar/39Ar results agree best where there is a relatively large amount of radiogenic 40Ar (>10%), and where the 40Ar/36Ar intercept calculated from the Ar isochron diagram is close to the atmospheric value. In two cases, it is not clear why U–Th/He and 40Ar/39Ar ages do not agree within uncertainty. U–Th/He and 40Ar/39Ar results diverge the most on a low-K transitional tholeiitic basalt with abundant olivine. For the most alkalic basalts with negligible olivine phenocrysts, U–Th/He ages were unattainable while 40Ar/39Ar results provide good precision even on ages as low as 19 ± 4 ka. Hence, the strengths and weaknesses of the U–Th/He and 40Ar/39Ar methods are complimentary for basalts with ages of order 100–500 ka. |
| first_indexed | 2025-11-14T08:34:52Z |
| format | Journal Article |
| id | curtin-20.500.11937-33956 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T08:34:52Z |
| publishDate | 2010 |
| publisher | Pergamon-Elsevier Science Ltd |
| recordtype | eprints |
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| spelling | curtin-20.500.11937-339562019-02-19T04:27:57Z Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii Aciego, S. Jourdan, Fred DePaolo, D. Kennedy, B. Late Quaternary, post-shield lavas from the Mauna Kea and Kohala volcanoes on the Big Island of Hawaii have been dated using the 40Ar/39Ar and U–Th/He methods. The objective of the study is to compare the recently demonstrated U–Th/He age method, which uses basaltic olivine phenocrysts, with 40Ar/39Ar ages measured on groundmass from the same samples. As a corollary, the age data also increase the precision of the chronology of volcanism on the Big Island. For the U–Th/He ages, U, Th and He concentrations and isotopes were measured to account for U-series disequilibrium and initial He. Single analyses U–Th/He ages for Hamakua lavas from Mauna Kea are 87 ± 40 to 119 ± 23 ka (2σ uncertainties), which are in general equal to or younger than 40Ar/39Ar ages. Basalt from the Polulu sequence on Kohala gives a U–Th/He age of 354 ± 54 ka and a 40Ar/39Ar age of 450 ± 40 ka. All of the U–Th/He ages, and all but one spurious 40Ar/39Ar ages conform to the previously proposed stratigraphy and published 14C and K–Ar ages.The ages also compare favorably to U–Th whole rock–olivine ages calculated from 238U–230Th disequilibria. The U–Th/He and 40Ar/39Ar results agree best where there is a relatively large amount of radiogenic 40Ar (>10%), and where the 40Ar/36Ar intercept calculated from the Ar isochron diagram is close to the atmospheric value. In two cases, it is not clear why U–Th/He and 40Ar/39Ar ages do not agree within uncertainty. U–Th/He and 40Ar/39Ar results diverge the most on a low-K transitional tholeiitic basalt with abundant olivine. For the most alkalic basalts with negligible olivine phenocrysts, U–Th/He ages were unattainable while 40Ar/39Ar results provide good precision even on ages as low as 19 ± 4 ka. Hence, the strengths and weaknesses of the U–Th/He and 40Ar/39Ar methods are complimentary for basalts with ages of order 100–500 ka. 2010 Journal Article http://hdl.handle.net/20.500.11937/33956 10.1016/j.gca.2009.11.020 Pergamon-Elsevier Science Ltd fulltext |
| spellingShingle | Aciego, S. Jourdan, Fred DePaolo, D. Kennedy, B. Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii |
| title | Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii |
| title_full | Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii |
| title_fullStr | Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii |
| title_full_unstemmed | Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii |
| title_short | Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii |
| title_sort | combined u–th/he and 40ar/39ar geochronology of post-shield lavas from the mauna kea and kohala volcanoes, hawaii |
| url | http://hdl.handle.net/20.500.11937/33956 |