Inter- and intra-crystal quartz δ18O homogeneity at Okataina volcano, Aotearoa New Zealand: Implications for rhyolite genesis

Sas M; Shane P; Kawasaki N; Sakamoto N; Zellmer GF; Yurimoto H

Inter- and intra-crystal quartz δ18O homogeneity at Okataina volcano, Aotearoa New Zealand: Implications for rhyolite genesis

dc.citation.issue	January 2022
dc.citation.volume	421
dc.contributor.author	Sas M
dc.contributor.author	Shane P
dc.contributor.author	Kawasaki N
dc.contributor.author	Sakamoto N
dc.contributor.author	Zellmer GF
dc.contributor.author	Yurimoto H
dc.date.accessioned	2024-11-18T02:16:51Z
dc.date.available	2024-11-18T02:16:51Z
dc.date.issued	2022-01
dc.description.abstract	The sources and processes involved in the genesis of the voluminous rhyolitic magmas of cataclysmic caldera-forming eruptions, and the intervening lower-volume intra-caldera extrusions, have been subject to much debate. To better understand generation of high-volume and low-volume silicic eruptions within a single volcanic centre, and how they may differ, we examined ten volumetrically varied high-SiO2 rhyolite eruptions from the Okataina Volcanic Centre (OVC) in Aotearoa New Zealand. The OVC is one of the world's most recurrently active silicic volcanoes. In the last ~600 ky, the OVC was the focus of three known caldera-forming events and numerous intermittent dome-building and fissure eruption episodes, with rhyolitic eruption activity as recent as 1314 CE. To elucidate how mass contributions from the mantle and crust may have fluctuated over the lifespan of the OVC magmatic system, oxygen isotopic ratios (δ18O) of quartz in rhyolites were investigated for the first time at inter-crystal and intra-crystal scales. Quartz crystals from four eruption episodes (two caldera-forming events, Utu, ~557 ka, Rotoiti, ~45 ka, and two intra-caldera dome-building events, Rotoma, ~9.5 ka, and Kaharoa, ~0.7 ka) yielded intra-crystal δ18O isotopic homogeneity (±0.23‰, 2sd) based on secondary ion mass spectrometry (SIMS). These samples also display inter-crystal and inter-unit homogeneity within slightly lower precision (7.6 ± 0.5‰, 2sd). Whole-crystal quartz from the same four units, as well as six other units (two intra-caldera dome-building episodes, Okareka, ~21.8 ka, Whakatane, ~5.5 ka, three pre-Rotoiti extra-caldera domes, Round Hill, Haparangi, Kakapiko, and one immediately post-Rotoiti eruption, Earthquake Flat), were then examined using high-precision laser fluorination. Single crystals also yielded mostly homogenous ratios with average δ18O = 7.6 ± 0.5‰ (2sd), which is consistent with intra-crystal SIMS analyses, albeit for a larger set of samples. Stable and radiogenic isotope mixing models using the newly obtained δ18O ratios demonstrate that OVC rhyolites can be produced by ≥25% assimilation of a regional (Torlesse-like) metasedimentary endmember by a depleted mantle source with slightly variable amounts of subduction flux, and that any incorporation of hydrothermally altered material to the system is limited to <5% in caldera and intra-caldera eruptions. The δ18O records of the OVC are among the most homogenous currently known and indicate stable and consistent mantle and crustal contributions across the lifespan of the magmatic system, with assimilation largely occurring prior to segregation of rhyolitic melts within the silicic reservoir. This isotopic homogeneity may be due to a relatively high-volume and constant magma flux at the OVC, which contrasts to other rhyolitic caldera volcanoes with greater isotopic variability.
dc.description.confidential	false
dc.identifier.author-url	http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000754627100003&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=c5bb3b2499afac691c2e3c1a83ef6fef
dc.identifier.citation	Sas M, Shane P, Kawasaki N, Sakamoto N, Zellmer GF, Yurimoto H. (2022). Inter- and intra-crystal quartz δ<sup>18</sup>O homogeneity at Okataina volcano, Aotearoa New Zealand: Implications for rhyolite genesis. Journal of Volcanology and Geothermal Research. 421. January 2022.
dc.identifier.doi	10.1016/j.jvolgeores.2021.107430
dc.identifier.eissn	1872-6097
dc.identifier.elements-type	journal-article
dc.identifier.issn	0377-0273
dc.identifier.number	ARTN 107430
dc.identifier.pii	S0377027321002596
dc.identifier.uri	https://mro.massey.ac.nz/handle/10179/72018
dc.language	English
dc.publisher	Elsevier B V, Amsterdam
dc.publisher.uri	https://www.sciencedirect.com/science/article/pii/S0377027321002596
dc.relation.isPartOf	Journal of Volcanology and Geothermal Research
dc.rights	(c) 2022 The Author/s
dc.rights	CC BY-NC-ND 4.0
dc.rights.uri	https://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject	Stable isotopes
dc.subject	Caldera
dc.subject	Petrogenesis
dc.subject	Rhyolite
dc.subject	Quartz
dc.title	Inter- and intra-crystal quartz δ18O homogeneity at Okataina volcano, Aotearoa New Zealand: Implications for rhyolite genesis
dc.type	Journal article
pubs.elements-id	450003
pubs.organisational-group	Other