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dc.contributor.authorChamberlain, Katy J.en
dc.contributor.authorWilson, Colin J. N.en
dc.contributor.authorWallace, Paul J.en
dc.contributor.authorMillet, Marli Bryanten
dc.date.accessioned2018-03-13T12:22:51Z
dc.date.available2018-03-13T12:22:51Z
dc.date.issued2015-04-23
dc.identifier.citationChamberlain, K. J. et al (2015) 'Micro-analytical Perspectives on the Bishop Tuff and its Magma Chamber', Journal of Petrology, 56 (3):605.en
dc.identifier.issn00223530
dc.identifier.issn14602415
dc.identifier.doi10.1093/petrology/egv012
dc.identifier.urihttp://hdl.handle.net/10545/622294
dc.description.abstractNew in situ major and trace element analytical data are presented for crystals (sanidine, plagioclase, biotite, orthopyroxene, clinopyroxene) and matrix glasses from juvenile materials representing the full Bishop Tuff sequence from the earliest fall unit (F1) to the latest ignimbrite package (Ig2Nc). These data are combined with published information to investigate the nature and zonation of the pre-eruptive Bishop magma chamber. Our data confirm that this magma chamber was a single unitary body that was thermally and compositionally zoned. The zonation was largely established prior to the growth of crystals, and also prior to mixing in the lower parts of the chamber induced by late-stage intrusion of a magma of contrasting composition and slightly higher temperature (the ‘bright-rim’ magma). Sparse mixed swirly and dacitic pumices show enrichments in Ba, Sr and Ti that identify these pumices as possible representatives of the ‘bright-rim’ magma. A model (revised from previously published work) for the pre-eruptive magma chamber comprises three main parts: (1) an upper, volumetrically dominant (∼2/3), relatively unzoned region that was the source of the earlier, eastern-erupted ignimbrite units and their coeval fall units; (2) a volumetrically minor transition zone that shows evidence for minor degrees of mixing and was the dominant source for the latest, eastern-erupted part of Ig1Eb (Sherwin subunit) and the earlier part of the northern-erupted ignimbrite (Ig 2Na); (3) a lower, volumetrically subordinate (∼1/3) region that was affected by mixing with the ‘bright-rim’ invasive magma in the lead-up to the eruption, and fed later northern-erupted units. Ingress of the ‘bright-rim’ magma introduced orthopyroxene and bright-rimmed zircon crystals, and induced partial resorption then overgrowth of rims enriched in Ti, Sr and Ba on sanidine and quartz, and development of zoning in clinopyroxene. Based on pumice proportions and associated crystal and glass chemistries through the eruptive sequence, we infer that the roof and floor of the magma chamber were stepped down to the north, such that the transition zone magma formed the floor of the southern part of the melt-dominant chamber and the roof of the northern part. Our data reinforce the previous concept of a single compositionally and thermally zoned Bishop magma chamber and additionally support a temporally constrained role for pre-eruptive magma mixing and the introduction of melts and minerals with contrasting compositions to the resident Bishop magma.
dc.description.sponsorshipK.J.C. acknowledges with thanks the receipt of a New Zealand International Doctoral Research Scholarship, administered by Education New Zealand. We also acknowledge generous support from the Marsden Fund (grant VUW0813) and award of a James Cook Fellowship to C.J.N.W., both administered by the Royal Society of New Zealand. Fieldwork by K.J.C. was partially supported by a Kleinman Award, administered by the US Geological Survey and by grants from the Faculty of Science at Victoria University.en
dc.language.isoenen
dc.publisherOxford Academicen
dc.relation.urlhttps://academic.oup.com/petrology/article-lookup/doi/10.1093/petrology/egv012en
dc.rightsArchived with thanks to Journal of Petrologyen
dc.subjectBishop Tuffen
dc.subjectSupereruptionen
dc.subjectMagma chamber processesen
dc.subjectPetrogenesisen
dc.subjectMagma stratificationen
dc.subjectGeologyen
dc.titleMicro-analytical perspectives on the Bishop Tuff and its magma chamber.en
dc.typeArticleen
dc.contributor.departmentVictoria University of Wellingtonen
dc.contributor.departmentDurham Universityen
dc.contributor.departmentUniversity of Oregonen
dc.identifier.journalJournal of Petrologyen
refterms.dateFOA2018-06-13T00:00:00Z
html.description.abstractNew in situ major and trace element analytical data are presented for crystals (sanidine, plagioclase, biotite, orthopyroxene, clinopyroxene) and matrix glasses from juvenile materials representing the full Bishop Tuff sequence from the earliest fall unit (F1) to the latest ignimbrite package (Ig2Nc). These data are combined with published information to investigate the nature and zonation of the pre-eruptive Bishop magma chamber. Our data confirm that this magma chamber was a single unitary body that was thermally and compositionally zoned. The zonation was largely established prior to the growth of crystals, and also prior to mixing in the lower parts of the chamber induced by late-stage intrusion of a magma of contrasting composition and slightly higher temperature (the ‘bright-rim’ magma). Sparse mixed swirly and dacitic pumices show enrichments in Ba, Sr and Ti that identify these pumices as possible representatives of the ‘bright-rim’ magma. A model (revised from previously published work) for the pre-eruptive magma chamber comprises three main parts: (1) an upper, volumetrically dominant (∼2/3), relatively unzoned region that was the source of the earlier, eastern-erupted ignimbrite units and their coeval fall units; (2) a volumetrically minor transition zone that shows evidence for minor degrees of mixing and was the dominant source for the latest, eastern-erupted part of Ig1Eb (Sherwin subunit) and the earlier part of the northern-erupted ignimbrite (Ig 2Na); (3) a lower, volumetrically subordinate (∼1/3) region that was affected by mixing with the ‘bright-rim’ invasive magma in the lead-up to the eruption, and fed later northern-erupted units. Ingress of the ‘bright-rim’ magma introduced orthopyroxene and bright-rimmed zircon crystals, and induced partial resorption then overgrowth of rims enriched in Ti, Sr and Ba on sanidine and quartz, and development of zoning in clinopyroxene. Based on pumice proportions and associated crystal and glass chemistries through the eruptive sequence, we infer that the roof and floor of the magma chamber were stepped down to the north, such that the transition zone magma formed the floor of the southern part of the melt-dominant chamber and the roof of the northern part. Our data reinforce the previous concept of a single compositionally and thermally zoned Bishop magma chamber and additionally support a temporally constrained role for pre-eruptive magma mixing and the introduction of melts and minerals with contrasting compositions to the resident Bishop magma.


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