Chemical and isotopic changes induced by pyrometamorphism in metasedimentary xenoliths at Tongariro volcano, New Zealand

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dc.contributor.authorPure, Leo R.
dc.contributor.authorCharlier, Bruce L. A.
dc.contributor.authorWilson, Colin J. N.
dc.contributor.authorGamble, John A.
dc.contributor.authorVry, Julie K.
dc.contributor.authorTownsend, Dougal B.
dc.contributor.authorLeonard, Graham S.
dc.contributor.funderVictoria University of Wellingtonen
dc.contributor.funderMinistry of Business, Innovation and Employmenten
dc.contributor.funderGNS Science, New Zealanden
dc.contributor.funderEarthquake Commission of New Zealanden
dc.date.accessioned2021-08-12T11:15:17Z
dc.date.available2021-08-12T11:15:17Z
dc.date.issued2021-08-04
dc.date.updated2021-08-12T10:43:24Z
dc.description.abstractAndesites erupted from Tongariro volcano, North Island, New Zealand contain feldspathic and quartzose xenoliths derived from basement rocks. New major oxide, trace element and Sr-Nd-Pb isotopic data indicate that both the Waipapa and Kaweka (meta)sedimentary terranes are represented in erupted xenoliths, rather than only the Kaweka terrane as previously thought. Xenolith mineral assemblages differ from their likely source materials, notably through the lack of white mica, illite, chlorite and quartz, which is reflected in contrasting chemical and isotopic compositions. Major and trace element data indicate that most xenoliths underwent bulk mass decreases of about 50% when pyrometamorphosed at temperatures of ~800–980 °C, similar to typical Tongariro magma temperatures of ~800–1000 °C. Bulk Eu concentrations were retained (in restitic plagioclase); however, other rare earth elements are commonly lower in xenoliths than in protoliths. In xenoliths, the 143Nd/144Nd ratios of protoliths were also retained, which indicates that xenoliths were derived from the Kaweka and Waipapa terranes in subequal amounts. Reductions in 87Sr/86Sr ratios by up to 0.003 in xenoliths, relative to their likely protoliths, were accompanied by decreases in Rb/Sr ratios from 0.1–0.8 down to <0.1, reflecting the dissolution of hydrous, Rb-rich minerals (white mica ± illite) with their radiogenic isotopic ingrowths liberated into surrounding andesitic magmas. Varied amounts of U/Pb, Th/Pb and Th/U fractionation demonstrably occurred between xenoliths and protoliths, but these are challenging to correlate with Pb isotopic fractionation that also occurred. One xenolith contains a vein of clinopyroxene, calcic plagioclase, silicic glass and graphite that formed when quartz + calcite veins were pyrometamorphosed. The vein-bearing xenolith possesses unusual chemical and isotopic features, which include a negative Ce anomaly, LaN/YbN ~ 2 and high 143Nd/144Nd (0.51284), which are also reported for xenolithic material erupted at neighbouring Ruapehu volcano.en
dc.description.sponsorshipVictoria University of Wellington (PhD Scholarship); Ministry of Business, Innovation and Employment, New Zealand (ECLIPSE Programme); Earthquake Commission of New Zealand (grant 16/U735)en
dc.description.statusPeer revieweden
dc.description.versionAccepted Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.articleid106404en
dc.identifier.citationPure, L. R., Charlier, B. L. A., Wilson, C. J. N., Gamble, J. A., Vry, J. K., Townsend, D. B. and Leonard, G. S. (2021) 'Chemical and isotopic changes induced by pyrometamorphism in metasedimentary xenoliths at Tongariro volcano, New Zealand', Lithos, 106404. doi: 10.1016/j.lithos.2021.106404en
dc.identifier.doi10.1016/j.lithos.2021.106404en
dc.identifier.issn0024-4937
dc.identifier.journaltitleLithosen
dc.identifier.urihttps://hdl.handle.net/10468/11734
dc.language.isoenen
dc.publisherElsevier B.V.en
dc.rights© 2021, Elsevier B.V. All rights reserved. This manuscript version is made available under the CC BY-NC-ND 4.0 license.en
dc.rights.urihttps://creativecommons.org/licenses/by-nc-nd/4.0/en
dc.subjectFractionationen
dc.subjectMetasedimentaryen
dc.subjectPyrometamorphismen
dc.subjectAndesiteen
dc.subjectRestiteen
dc.subjectXenolithen
dc.titleChemical and isotopic changes induced by pyrometamorphism in metasedimentary xenoliths at Tongariro volcano, New Zealanden
dc.typeArticle (peer-reviewed)en
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