title: Volcanology and secondary alteration of the 1.6 Ma Ngaroma Ignimbrite, Upper Waipari Valley

authors: Ross, ChrisAnne

subjects: Taupo Volcanic Zone (TVZ)

abstract: The 1.6 Ma Ngaroma eruption from the Mangakino Volcanic Centre (MVC) is the first known rhyolitic event of the Taupo Volcanic Zone (TVZ), and variations of primary components recorded throughout the Ngaroma Ignimbrite provide insight(s) into pre-eruptive processes and post-emplacement mechanisms.

A field study of the Ngaroma Ignimbrite was undertaken proximal to the source caldera (~25 km) around the township of Ngaroma. Two primary facies (a lithic- rich and lithic-poor facies) and four subfacies have been identified and are presented in four stratigraphic logs, which vary both vertically and laterally throughout the field area. The facies reflect syn- and post-deposition process that are identifiable from one another based on macroscopic observations including changes in primary componentry, the degree of welding and nature of secondary alteration. Variations in depositional structures and textures highlight the intense welding, limited incorporation of vent-derived lithics, and the absence of a pumice/ash fall deposit underlying the ignimbrite, which suggest that the parent pyroclastic flow formed from the immediate collapse of a highly explosive, caldera-forming eruption column.
Petrographic observations and mineralogic analyses involving optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) record high concentrations of sanidine and cristobalite, followed by clay minerals (kaolinite), which suggest the deposit endured significant post-emplacement processes such as vapour-phase alteration and devitrification. The ignimbrite matrix varies from a eutaxitic texture comprising (a) visible, well-formed, but devitrified, glass shards typically 300 to 800 μm, to (b) a fine-grained, homogenous, optically unresolvable medium; the latter can be resolved under SEM and comprises intergrown <3 μm- sized K-feldspar (sanidine), amorphous/nano-crystalline silica (cristobalite ± tridymite), and pore cavities.

Geochemical analyses of major and trace elements on bulk ignimbrite and pumice were determined using x-ray fluorescence (XRF) spectrometry and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and on individual minerals by electron microprobe analysis (EPMA). Samples used in these geochemical analyses have been pervasively altered, and that due to the lack or absence of primary material (fresh glass and pumice), some of the patterns observed here are presumed to in part reflect post alteration processes (vapour-phase alteration and devitrification) and therefore, are of limited use for understanding primary magmatic processes. The major and selective trace elements of bulk rock ignimbrite and pumice confirm a rhyolitic composition and are consistent with the effect of syn- and post-emplacement alteration processes. Geochemical signatures of rare earth elements (REE) observed on multielement diagrams are associated with subduction related magmas and indicative of crustal contamination. Major element compositions of both feldspar and pyroxene phenocrysts range from An₁₅₋ An₂₈ and Or₅₋Or₁₂ and from En₃₂ to En₄₁, respectively, and are typical composition of rhyolitic magmas.

text: Volcanology and secondary alteration of the 1.6 Ma Ngaroma Ignimbrite, Upper Waipari Valley The 1.6 Ma Ngaroma eruption from the Mangakino Volcanic Centre (MVC) is the first known rhyolitic event of the Taupo Volcanic Zone (TVZ), and variations of primary components recorded throughout the Ngaroma Ignimbrite provide insight(s) into pre-eruptive processes and post-emplacement mechanisms.

A field study of the Ngaroma Ignimbrite was undertaken proximal to the source caldera (~25 km) around the township of Ngaroma. Two primary facies (a lithic- rich and lithic-poor facies) and four subfacies have been identified and are presented in four stratigraphic logs, which vary both vertically and laterally throughout the field area. The facies reflect syn- and post-deposition process that are identifiable from one another based on macroscopic observations including changes in primary componentry, the degree of welding and nature of secondary alteration. Variations in depositional structures and textures highlight the intense welding, limited incorporation of vent-derived lithics, and the absence of a pumice/ash fall deposit underlying the ignimbrite, which suggest that the parent pyroclastic flow formed from the immediate collapse of a highly explosive, caldera-forming eruption column.
Petrographic observations and mineralogic analyses involving optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) record high concentrations of sanidine and cristobalite, followed by clay minerals (kaolinite), which suggest the deposit endured significant post-emplacement processes such as vapour-phase alteration and devitrification. The ignimbrite matrix varies from a eutaxitic texture comprising (a) visible, well-formed, but devitrified, glass shards typically 300 to 800 μm, to (b) a fine-grained, homogenous, optically unresolvable medium; the latter can be resolved under SEM and comprises intergrown <3 μm- sized K-feldspar (sanidine), amorphous/nano-crystalline silica (cristobalite ± tridymite), and pore cavities.

Geochemical analyses of major and trace elements on bulk ignimbrite and pumice were determined using x-ray fluorescence (XRF) spectrometry and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and on individual minerals by electron microprobe analysis (EPMA). Samples used in these geochemical analyses have been pervasively altered, and that due to the lack or absence of primary material (fresh glass and pumice), some of the patterns observed here are presumed to in part reflect post alteration processes (vapour-phase alteration and devitrification) and therefore, are of limited use for understanding primary magmatic processes. The major and selective trace elements of bulk rock ignimbrite and pumice confirm a rhyolitic composition and are consistent with the effect of syn- and post-emplacement alteration processes. Geochemical signatures of rare earth elements (REE) observed on multielement diagrams are associated with subduction related magmas and indicative of crustal contamination. Major element compositions of both feldspar and pyroxene phenocrysts range from An₁₅₋ An₂₈ and Or₅₋Or₁₂ and from En₃₂ to En₄₁, respectively, and are typical composition of rhyolitic magmas.

year: 2020

title: Exact and quasiexact solvability of second-order superintegrable quantum systems: I. Euclidean space preliminaries

authors: Kalnins, Ernie G.

subjects: Mathematics

abstract: We show that second-order superintegrable systems in two-dimensional and three-dimensional Euclidean space generate both exactly solvable (ES) and quasiexactly solvable (QES) problems in quantum mechanics via separation of variables, and demonstrate the increased insight into the structure of such problems provided by superintegrability. A principal advantage of our analysis using nondegenerate superintegrable systems is that they are multiseparable. Most past separation of variables treatments of QES problems via partial differential equations have only incorporated separability, not multiseparability. Also, we propose another definition of ES and QES. The quantum mechanical problem is called ES if the solution of Schrödinger equation can be expressed in terms of hypergeometric functions mFn and is QES if the Schrödinger equation admits polynomial solutions with coefficients necessarily satisfying a three-term or higher order of recurrence relations. In three dimensions we give an example of a system that is QES in one set of separable coordinates, but is not ES in any other separable coordinates. This example encompasses Ushveridze's tenth-order polynomial QES problem in one set of separable coordinates and also leads to a fourth-order polynomial QES problem in another separable coordinate set.

text: Exact and quasiexact solvability of second-order superintegrable quantum systems: I. Euclidean space preliminaries We show that second-order superintegrable systems in two-dimensional and three-dimensional Euclidean space generate both exactly solvable (ES) and quasiexactly solvable (QES) problems in quantum mechanics via separation of variables, and demonstrate the increased insight into the structure of such problems provided by superintegrability. A principal advantage of our analysis using nondegenerate superintegrable systems is that they are multiseparable. Most past separation of variables treatments of QES problems via partial differential equations have only incorporated separability, not multiseparability. Also, we propose another definition of ES and QES. The quantum mechanical problem is called ES if the solution of Schrödinger equation can be expressed in terms of hypergeometric functions mFn and is QES if the Schrödinger equation admits polynomial solutions with coefficients necessarily satisfying a three-term or higher order of recurrence relations. In three dimensions we give an example of a system that is QES in one set of separable coordinates, but is not ES in any other separable coordinates. This example encompasses Ushveridze's tenth-order polynomial QES problem in one set of separable coordinates and also leads to a fourth-order polynomial QES problem in another separable coordinate set.

year: 2006-03

title: Place imaginaries: Photography and place-making at Te Awa River Ride

authors: Hill, Rodrigo

subjects: photography

abstract: Contemporary photographic practice has evolved into a field of possibilities, which includes a flux of representational modes that depict experiences, feelings and emotions. This PhD with Creative Practice Components investigates how photography is embedded within ways of knowing, experiencing and making places and the subsequent visual constructions of place imaginaries.  Drawing on contemporary photographic practice and theory, I position myself as a qualitative researcher engaged in creative practice, specifically lens-based approaches and modes of photographic representation. In contrast to photography’s dominant discourse centred on indexical and objective assumptions, I understand photographic practices and images as constructions of multiple meanings.

I use Te Awa River Ride as my research locale, a place where different practices and discourses entangle, forming a diverse set of dynamic and intersecting meanings. Te Awa River Ride is a shared pathway, with a planned total length of 70 kilometres, that edges the banks of the Waikato River from Ngāruawāhia to Cambridge, in the central North Island of Aotearoa New Zealand. I understand Te Awa River Ride as a place-composite, layered by multiple place imaginaries, including indigenous Māori, Pākehā and European ways of meaning and place-making. In this thesis I draw upon place imaginaries as a way of expressing visual possibilities, constructions and affective responses to my own and others’ experiences at this unique research location. 

My photography practice aims to actualise particular place imaginaries through curation and sequencing of lens-based explorations of light, movement and water. This process and the compilation of imagery into curatorial products, such as photography installations, generate novel ways of perceiving the Waikato River and Te Awa River Ride, revealing the centrality of photography in place-making processes.

text: Place imaginaries: Photography and place-making at Te Awa River Ride Contemporary photographic practice has evolved into a field of possibilities, which includes a flux of representational modes that depict experiences, feelings and emotions. This PhD with Creative Practice Components investigates how photography is embedded within ways of knowing, experiencing and making places and the subsequent visual constructions of place imaginaries.  Drawing on contemporary photographic practice and theory, I position myself as a qualitative researcher engaged in creative practice, specifically lens-based approaches and modes of photographic representation. In contrast to photography’s dominant discourse centred on indexical and objective assumptions, I understand photographic practices and images as constructions of multiple meanings.

I use Te Awa River Ride as my research locale, a place where different practices and discourses entangle, forming a diverse set of dynamic and intersecting meanings. Te Awa River Ride is a shared pathway, with a planned total length of 70 kilometres, that edges the banks of the Waikato River from Ngāruawāhia to Cambridge, in the central North Island of Aotearoa New Zealand. I understand Te Awa River Ride as a place-composite, layered by multiple place imaginaries, including indigenous Māori, Pākehā and European ways of meaning and place-making. In this thesis I draw upon place imaginaries as a way of expressing visual possibilities, constructions and affective responses to my own and others’ experiences at this unique research location. 

My photography practice aims to actualise particular place imaginaries through curation and sequencing of lens-based explorations of light, movement and water. This process and the compilation of imagery into curatorial products, such as photography installations, generate novel ways of perceiving the Waikato River and Te Awa River Ride, revealing the centrality of photography in place-making processes.

year: 2019