1 10 1 https://theses.otagogeology.org.nz/files/original/8a16ab04ccdeccf48feed1874cf0cbcd.pdf dd468a74dc4b461dfe2ecefd93bcab76 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Author last name Last name of the Author Lewis Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? MSc Advisers Who supervised/advised this student White, J.D.L. Abstract The Abstract for this thesis The Potaka Tephra was deposited in a range of conditions across the Wanganui Basin including: nearshore/delta front, restricted-sediment-input, nearshore marine environment, and mid-basin with highly variable sediment supply (paleobathymetry and lcaol current fluctuation controlled). Evidence exists for two stages of volcaniclastic sedimentation at Kai Iwi, the result of a delayed (relative to other localities) major influx of material to the site. A rapid influx of sediments is suggested by componentry, sedimentary structures, thickness, and a prograding delta environment. The main controls on this process is sediment supply. The Potaka Tephra is a good example of post volcanism sedimentary response in a distal basinal environment. The chemistry of the Potaka Tephra pumice-glass and ash shards ranges from ~72-78% SiO2. Minor variations in other elements occur non-systemically across all localities. Wholepumice compositions range from dacite to high SiO2 rhyolite. All pumice are peraluminous, and range from medium-high K2O. Phenocrysts make up 6-7.5% of the solid material in Potaka Tephra pumice. Phenocrysts identified are: plagioclase (73%), hornblende (8%), OPX (7%), iron oxides (5%), quartz (3%), biotite (3%), CPX (<0.5%), +/- accessory minerals apatite and zircon. Free crystals in the Potaka Tephra make up approximately 5-85% of the tephra depending on locality. The free crystal assemblage consists of: plagioclase feldspar, hornblende, OPX, CPX, quartz, biotite, muscovite, iron oxides, ± alkali feldspar, apatite, and zircons. The proportion of free crystals present in any one sample is highly varied. All glass and whole-pumice major and trace element compositions show minor compositional variations consistent with fractionation of the observed mineral assemblage ± monazite, allanite, and xenotime. Overall they look similar, and are suggestive of a single population. The Potaka Tephra trace element composition is nearly identical to that of the Kidnappers Ignimbrite and Fall Deposits. For the first time, a definitive correlation of the Potaka Tephra with the Kidnappers Fall and Ignimbrite Deposits can be made. Magma evolution in the Potaka tephra was dominated by plagioclase fractionation. No definitive evidence of magma mixing was seen. Trace element ratios suggest that the Potaka Tephra was sourced from two separate batches of magma (melt + crystals). Each batch of magma evolved by fractionation of plagioclase and zircon, but to different degrees. To produce chemical signatures like these, the magma batches would have to have been isolated from each other, either by chemical zoning or physical isolation. Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Whanganui Thesis description Number of pages, maps, CDs, etc. xviii, 304, [110] p. : col. ill., maps ; 30 cm. + 1 CD-ROM. Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2007Lewis Creator An entity primarily responsible for making the resource Lewis, Bridgette. Date A point or period of time associated with an event in the lifecycle of the resource 2007 Title A name given to the resource Eruptive source and depositional characteristics of the Potaka Tephra, Wanganui Basin, New Zealand Subject The topic of the resource Sedimentology Petrology depostition sedimentation volcanic ash Whanganui River Watershed