Combined U–Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii
MetadataShow full item record
NOTICE: This is the author’s version of a work that was accepted for publication in Geochimica et Cosmochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Geochimica et Cosmochimica Acta [74, 5, 2010] DOI 10.1016/j.gca.2009.11.020
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.
Showing items related by title, author, creator and subject.
Olivine-phyric basalt in the Mesoproterozoic Gawler silicic large igneous province, South Australia: Examples at the Olympic Dam Iron Oxide Cu-U-Au-Ag deposit and other localitiesHuang, Q.; Kamenetsky, V.; Ehrig, K.; McPhie, J.; Kamenetsky, M.; Cross, K.; Meffre, S.; Agangi, Andrea; Chambefort, I.; Direen, N.; Maas, R.; Apukhtina, O. (2016)The felsic-dominant Gawler Range Volcanics and cogenetic Hiltaba Suite granitoids constitute the ca. 1590 Ma Gawler silicic large igneous province in the Gawler Craton, South Australia. The province includes minor occurrences ...
Temperature, Pressure, and Composition of the Mantle Source Region of Late Cenozoic Basalts in Hainan Island, SE Asia: a Consequence of a Young Thermal Mantle Plume close to Subduction Zones?Wang, Xuan-Ce; Li, Zheng-Xiang; Li, X.; Li, J.; Liu, Y.; Long, W.; Zhou, J.; Wang, F. (2012)Basaltic lavas from Hainan Island near the northern edge of the South China Sea have an age range of between late Miocene (about 13 Ma) and Holocene, with a peak age of late Pliocene to middle Pleistocene. The basaltic ...
The mafic-ultramafic dykes in the Yanbian Terrane (Sichuan Province, SW China): Record of magma differentiation and emplacement in the Emeishan large igneous provinceMunteanu, M.; Wilson, A.; Costin, G.; Yao, Y.; Lum, J.; Jiang, S.; Jourdan, Fred; Chunnett, G.; Cioaca, M. (2017)© The Author 2017. Published by Oxford University Press. All rights reserved. Numerous olivine-rich dykes intruded the late Proterozoic Yanbian terrane, Sichuan, SW China. The dykes are less than 10m thick and show thin ...