title: Volcanic geology of the early Pleistocene ignimbrite succession in the western Papamoa Region, Bay of Plenty

authors: Namaliu, Miriam Darusila Mangon

abstract: Volcanic activity in the Tauranga Volcanic Center (TgaVC) occurred between 2.95 to 1.9 Ma, some of the eruptions were explosive and led to the distribution of ignimbrites of varying volumes across the western Bay of Plenty Region (Tauranga Basin), North Island. The Papamoa Formation forms part of the landscape in this area. This study was aimed at determining the volcanic history and processes involved in the distribution of the Papamoa Formation within the eastern Tauranga Basin.

Stratigraphic, petrographic and geochemical investigations were undertaken in the field and from samples within the study area. Field observations of the ignimbrites involved stratigraphic logging and lateral relationships, component measurements and lithological descriptions. Ignimbrite petrography was undertaken by optical microscopy. To determine the geochemical characteristics of the source magmas for the ignimbrites, the following analyses were conducted: electron microprobe analysis (EMPA) on glass shards extracted from the ignimbrite matrices, glass from pumice, and on minerals in the pumice, x-ray fluorescence spectroscopy (XRF) on whole pumice clasts and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on the same glass samples used for EMPA.

Five individual eruptions that led to the distribution of five ignimbrites have been identified within the ignimbrite succession of the Papamoa Formation: an early unnamed ignimbrite, followed by the Welcome Bay, Wharo, Arateka, and Otawera ignimbrites. The beige-brown, non-welded, pumice-rich, Welcome Bay Ignimbrite (2.4 Ma) is the most voluminous in the study area and also has an underlying pumice fall deposit. The dark brown to black, pumice-/fiamme-rich Wharo Ignimbrite (2.26 Ma, M. Prentice unpublished data, 2021) is the only moderate to densely welded ignimbrite. Both the Welcome Bay and Otawera ignimbrite contained black (andesitic-dacitic) and white (dacitic) pumice. The beige, non-welded Otawera Ignimbrite (2.21 Ma) is the least voluminous ignimbrite in the study area and comprises only white pumice. The beige-yellow brown Arateka ignimbrite is comprises of both the black and white pumice clasts. The unnamed Unit A ignimbrite, at the base of the succession has only one pumice population – grey pumice, but it is poorly exposed. All the ignimbrites are generally lithic poor. Petrographic analysis found that the main minerals occurring in the ignimbrites were: plagioclase, pyroxenes, hornblende and opaques. The main mineral in the black pumice was plagioclase and pyroxene. The white pumice, however, is mainly composed of plagioclase and hornblende. In terms of rock textures, the Welcome Bay Ignimbrite, Arateka Ignimbrite, Otawera Ignimbrite and Unit A-Unknown Ignimbrite had either a porphyritic or vitrophyric or a combination of both textures. The
Wharo Ignimbrite possessed a porphyritic and/or eutaxitic texture. Geochemical data showed that although the glass shards from each ignimbrite has a unique chemical composition, they were all rhyolitic. However, in terms of the two pumice types, the white pumice was dacitic while the black pumice was andesitic.

The presence of two pumice types (black and white) in the Welcome Bay, Wharo and Arateka Ignimbrites, supports the idea that the magma from which the ignimbrites were sourced, had a mixed andesitic to dacitic composition. The distribution and internal stratigraphy of the Papamoa Formation record a history of multiple ignimbrite-forming eruptions that were sourced locally, likely south of the study area; at least one ignimbrite (Welcome Bay Ignimbrite) was preceded by a sustained Plinian eruption column.

text: Volcanic geology of the early Pleistocene ignimbrite succession in the western Papamoa Region, Bay of Plenty Volcanic activity in the Tauranga Volcanic Center (TgaVC) occurred between 2.95 to 1.9 Ma, some of the eruptions were explosive and led to the distribution of ignimbrites of varying volumes across the western Bay of Plenty Region (Tauranga Basin), North Island. The Papamoa Formation forms part of the landscape in this area. This study was aimed at determining the volcanic history and processes involved in the distribution of the Papamoa Formation within the eastern Tauranga Basin.

Stratigraphic, petrographic and geochemical investigations were undertaken in the field and from samples within the study area. Field observations of the ignimbrites involved stratigraphic logging and lateral relationships, component measurements and lithological descriptions. Ignimbrite petrography was undertaken by optical microscopy. To determine the geochemical characteristics of the source magmas for the ignimbrites, the following analyses were conducted: electron microprobe analysis (EMPA) on glass shards extracted from the ignimbrite matrices, glass from pumice, and on minerals in the pumice, x-ray fluorescence spectroscopy (XRF) on whole pumice clasts and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on the same glass samples used for EMPA.

Five individual eruptions that led to the distribution of five ignimbrites have been identified within the ignimbrite succession of the Papamoa Formation: an early unnamed ignimbrite, followed by the Welcome Bay, Wharo, Arateka, and Otawera ignimbrites. The beige-brown, non-welded, pumice-rich, Welcome Bay Ignimbrite (2.4 Ma) is the most voluminous in the study area and also has an underlying pumice fall deposit. The dark brown to black, pumice-/fiamme-rich Wharo Ignimbrite (2.26 Ma, M. Prentice unpublished data, 2021) is the only moderate to densely welded ignimbrite. Both the Welcome Bay and Otawera ignimbrite contained black (andesitic-dacitic) and white (dacitic) pumice. The beige, non-welded Otawera Ignimbrite (2.21 Ma) is the least voluminous ignimbrite in the study area and comprises only white pumice. The beige-yellow brown Arateka ignimbrite is comprises of both the black and white pumice clasts. The unnamed Unit A ignimbrite, at the base of the succession has only one pumice population – grey pumice, but it is poorly exposed. All the ignimbrites are generally lithic poor. Petrographic analysis found that the main minerals occurring in the ignimbrites were: plagioclase, pyroxenes, hornblende and opaques. The main mineral in the black pumice was plagioclase and pyroxene. The white pumice, however, is mainly composed of plagioclase and hornblende. In terms of rock textures, the Welcome Bay Ignimbrite, Arateka Ignimbrite, Otawera Ignimbrite and Unit A-Unknown Ignimbrite had either a porphyritic or vitrophyric or a combination of both textures. The
Wharo Ignimbrite possessed a porphyritic and/or eutaxitic texture. Geochemical data showed that although the glass shards from each ignimbrite has a unique chemical composition, they were all rhyolitic. However, in terms of the two pumice types, the white pumice was dacitic while the black pumice was andesitic.

The presence of two pumice types (black and white) in the Welcome Bay, Wharo and Arateka Ignimbrites, supports the idea that the magma from which the ignimbrites were sourced, had a mixed andesitic to dacitic composition. The distribution and internal stratigraphy of the Papamoa Formation record a history of multiple ignimbrite-forming eruptions that were sourced locally, likely south of the study area; at least one ignimbrite (Welcome Bay Ignimbrite) was preceded by a sustained Plinian eruption column.

year: 2021

title: Influence of loading rate, alkali fibre treatment and crystallinity on fracture toughness of random short hemp fibre reinforced polylactide bio-composites

authors: Pickering, Kim L.

subjects: Polymer-matrix composites (PMCs)

abstract: Plane-strain fracture toughness (KIc) of random short hemp fibre reinforced polylactide (PLA) bio-composites was investigated along with the effect of loading rate, fibre treatment and PLA crystallinity. Fracture toughness testing was carried out at loading rates varying from 0.5 to 20 mm/min using single-edge-notched bending specimens with 0 to 30 wt% fibre. KQ (trial KIc) of composites decreased as loading rate increased, until stabilising to give KIc values at a loading rate of 10 mm/min and higher. The reduction of crazing and stress whitening, as well as a more direct crack path observed in PLA samples combined with reduced plastic deformation observed in composites provided explanation for this reduction. KIc of composites was found to decrease with increased fibre content and fibre treatment with sodium hydroxide. Studies controlling the degree of PLA crystallinity by heat treatment or “annealing” showed that reduction of KIc can be attributed to increased crystallinity.

text: Influence of loading rate, alkali fibre treatment and crystallinity on fracture toughness of random short hemp fibre reinforced polylactide bio-composites Plane-strain fracture toughness (KIc) of random short hemp fibre reinforced polylactide (PLA) bio-composites was investigated along with the effect of loading rate, fibre treatment and PLA crystallinity. Fracture toughness testing was carried out at loading rates varying from 0.5 to 20 mm/min using single-edge-notched bending specimens with 0 to 30 wt% fibre. KQ (trial KIc) of composites decreased as loading rate increased, until stabilising to give KIc values at a loading rate of 10 mm/min and higher. The reduction of crazing and stress whitening, as well as a more direct crack path observed in PLA samples combined with reduced plastic deformation observed in composites provided explanation for this reduction. KIc of composites was found to decrease with increased fibre content and fibre treatment with sodium hydroxide. Studies controlling the degree of PLA crystallinity by heat treatment or “annealing” showed that reduction of KIc can be attributed to increased crystallinity.

year: 2011

title: A Journey Beyond the Bars: Participants' Experiences of Psychological Treatment in a Prison Setting

authors: Terrill, Damian James

subjects: Prison

abstract: This study explored the experiences of high-risk male offenders at varying stages of a prison-based residential rehabilitation programme. Information was elicited by means of 1:1 semi-structured interviews with three adult offenders: one programme completer, one approaching completion and one non-completer. The opinions of three members of unit staff (two programme facilitators and one custodial officer) were also included. Having identified a lack of process-focused qualitative research in the criminological literature, this thesis has attempted to provide an insight into the lived experiences of offenders undergoing a residential rehabilitative intervention. The results are presented through a combined postmodernist, social constructionist discourse. They identify a series of coherent themes which emphasise the importance of numerous contextual, linguistic and communicative variables in dictating the participants’ self-perspectives and engagement with treatment. I will examine in particular, the role of motivation, the importance of the therapeutic bond established between participants and therapists, the relevance of the therapeutic environment, and the impact of both bi-cultural therapy and notions of individual stigmatisation. The overall findings are related to the broader penological literature in order to inspire further experiential analyses of offenders undergoing treatment, and to offer points for consideration in the application of prison-based rehabilitative interventions.

text: A Journey Beyond the Bars: Participants' Experiences of Psychological Treatment in a Prison Setting This study explored the experiences of high-risk male offenders at varying stages of a prison-based residential rehabilitation programme. Information was elicited by means of 1:1 semi-structured interviews with three adult offenders: one programme completer, one approaching completion and one non-completer. The opinions of three members of unit staff (two programme facilitators and one custodial officer) were also included. Having identified a lack of process-focused qualitative research in the criminological literature, this thesis has attempted to provide an insight into the lived experiences of offenders undergoing a residential rehabilitative intervention. The results are presented through a combined postmodernist, social constructionist discourse. They identify a series of coherent themes which emphasise the importance of numerous contextual, linguistic and communicative variables in dictating the participants’ self-perspectives and engagement with treatment. I will examine in particular, the role of motivation, the importance of the therapeutic bond established between participants and therapists, the relevance of the therapeutic environment, and the impact of both bi-cultural therapy and notions of individual stigmatisation. The overall findings are related to the broader penological literature in order to inspire further experiential analyses of offenders undergoing treatment, and to offer points for consideration in the application of prison-based rehabilitative interventions.

year: 2010