title: Geophysical characterisation of the Onewhero and Kellyville volcanic complexes, South Auckland Volcanic Field

authors: Mullane, Kevin Joseph Chase

subjects: South Auckland Volcanic Field

abstract: The Quaternary-aged (1.59 – 0.51 Ma) intraplate, monogenetic, basaltic South Auckland Volcanic Field consists of at least 82 volcanic centres that span an area of 300 km². This study focusses on the volcanic and sedimentary histories of the Onewhero and Kellyville maars, interpreted from additional geological observations, which build upon previous geological studies, and gravimetric and magnetic surveys.
New geological observations of the Onewhero maar reveal the presence of diatomaceous sediment, and at least one lava flow, that probably originated from the nearby Klondyke cone to the south, and which occupies a significant area of the crater floor. A geological investigation of the Kellyville maar reveals a crater that has been partially filled by a thick accumulation of basalt and scoria and overlain by Karapiro Formation sediments and diatomite. Available borehole stratigraphy suggests that the Glass Hill basalt cone present in the Kellyville maar was an early-stage volcanic product rather than a late-stage product as previously thought.
Gravimetric surveys in the Onewhero and Kellyville maars revealed contrasting crater fill deposits. Raw gravity data was acquired in the field, corrected for drift and then reduced to a Bouguer anomaly. The Onewhero maar is characterised by an anomaly of -5.8 mGal that has a concave profile. The post-eruption geological body present at Onewhero is two-dimensionally modelled with a density of 1.3 g/cm³, and has a maximum thickness of 100 m in the northwest of the crater. The Kellyville maar is characterised by an anomaly of +2.5 mGal that has a convex profile. The dominant geological body present in the crater is a lava-lake deposit that is two-dimensionally modelled with a density of 2.9 g/cm³, and has a maximum thickness of 60 m.
The total magnetic field strength of the Onewhero and Kellyville maars was recorded with a proton magnetometer and the values were mapped in ArcMap. In the Onewhero maar, two subdued anomalies were outliers. A positive magnetic anomaly (213 nT) with a broad crescent shape was identified in the middle of the crater and interpreted to be either an extrusive feeder dyke or an accumulation of highly magnetic volcanic sediment deposited in a topographic trough. A circular negative anomaly (-1057 nT) in the northwest of the crater is an accumulation of lake sediment with a low magnetic susceptibility. In the Kellyville maar, two contrasting anomalies were observed. The strongly positive anomaly (1275 nT) corresponds to the geographical position of Glass Hill, a basaltic cone. A strong negative anomaly (-3315 nT) in the middle of the crater corresponds to a known deposit of diatomite.
Overall, the structure of the Onewhero maar, as inferred by this investigation, is similar to many other maars globally and its sedimentary fill is remarkably similar to the Dottingen maar in Germany. The Kellyville maar has a more unique structure but can be compared to the Domain maar in the nearby Auckland Volcanic Field.

text: Geophysical characterisation of the Onewhero and Kellyville volcanic complexes, South Auckland Volcanic Field The Quaternary-aged (1.59 – 0.51 Ma) intraplate, monogenetic, basaltic South Auckland Volcanic Field consists of at least 82 volcanic centres that span an area of 300 km². This study focusses on the volcanic and sedimentary histories of the Onewhero and Kellyville maars, interpreted from additional geological observations, which build upon previous geological studies, and gravimetric and magnetic surveys.
New geological observations of the Onewhero maar reveal the presence of diatomaceous sediment, and at least one lava flow, that probably originated from the nearby Klondyke cone to the south, and which occupies a significant area of the crater floor. A geological investigation of the Kellyville maar reveals a crater that has been partially filled by a thick accumulation of basalt and scoria and overlain by Karapiro Formation sediments and diatomite. Available borehole stratigraphy suggests that the Glass Hill basalt cone present in the Kellyville maar was an early-stage volcanic product rather than a late-stage product as previously thought.
Gravimetric surveys in the Onewhero and Kellyville maars revealed contrasting crater fill deposits. Raw gravity data was acquired in the field, corrected for drift and then reduced to a Bouguer anomaly. The Onewhero maar is characterised by an anomaly of -5.8 mGal that has a concave profile. The post-eruption geological body present at Onewhero is two-dimensionally modelled with a density of 1.3 g/cm³, and has a maximum thickness of 100 m in the northwest of the crater. The Kellyville maar is characterised by an anomaly of +2.5 mGal that has a convex profile. The dominant geological body present in the crater is a lava-lake deposit that is two-dimensionally modelled with a density of 2.9 g/cm³, and has a maximum thickness of 60 m.
The total magnetic field strength of the Onewhero and Kellyville maars was recorded with a proton magnetometer and the values were mapped in ArcMap. In the Onewhero maar, two subdued anomalies were outliers. A positive magnetic anomaly (213 nT) with a broad crescent shape was identified in the middle of the crater and interpreted to be either an extrusive feeder dyke or an accumulation of highly magnetic volcanic sediment deposited in a topographic trough. A circular negative anomaly (-1057 nT) in the northwest of the crater is an accumulation of lake sediment with a low magnetic susceptibility. In the Kellyville maar, two contrasting anomalies were observed. The strongly positive anomaly (1275 nT) corresponds to the geographical position of Glass Hill, a basaltic cone. A strong negative anomaly (-3315 nT) in the middle of the crater corresponds to a known deposit of diatomite.
Overall, the structure of the Onewhero maar, as inferred by this investigation, is similar to many other maars globally and its sedimentary fill is remarkably similar to the Dottingen maar in Germany. The Kellyville maar has a more unique structure but can be compared to the Domain maar in the nearby Auckland Volcanic Field.

year: 2015

title: Ideology and the ANZUS dispute: the legacy of the New Left and the consequences for New Zealand’s security policy

authors: Sinclair, Brian James

abstract: This study of the ANZUS dispute examines the influence of the New Left’s ideology on NZ’s security discourse, and how the development of this ideology contributed to the rift between NZ and the US over the question of visits by US nuclear-powered or nuclear weapons-capable warships. In a break from past scholarship on the ANZUS dispute, this thesis examines the nature and history of the NZ peace movement, and it argues that New Left ideology became the main driving force of the peace movement after the 1960s. The NZ peace movement’s resulting desire to disengage NZ from military co-operation with the US was aided by the fact that, by 1984, the NZ Labour Party was also heavily influenced by the same ideology. Although the NZ public was supportive of ANZUS and collective security, its anti-nuclearism enabled the above organisations to impose a nuclear ship ban which resulted in an end to US military co-operation with NZ. This thesis uses a wide range of peace movement sources and other secondary sources to reveal the motivations lying behind the NZ ship ban, and to assess the consequences of the ban.

text: Ideology and the ANZUS dispute: the legacy of the New Left and the consequences for New Zealand’s security policy This study of the ANZUS dispute examines the influence of the New Left’s ideology on NZ’s security discourse, and how the development of this ideology contributed to the rift between NZ and the US over the question of visits by US nuclear-powered or nuclear weapons-capable warships. In a break from past scholarship on the ANZUS dispute, this thesis examines the nature and history of the NZ peace movement, and it argues that New Left ideology became the main driving force of the peace movement after the 1960s. The NZ peace movement’s resulting desire to disengage NZ from military co-operation with the US was aided by the fact that, by 1984, the NZ Labour Party was also heavily influenced by the same ideology. Although the NZ public was supportive of ANZUS and collective security, its anti-nuclearism enabled the above organisations to impose a nuclear ship ban which resulted in an end to US military co-operation with NZ. This thesis uses a wide range of peace movement sources and other secondary sources to reveal the motivations lying behind the NZ ship ban, and to assess the consequences of the ban.

year: 1998

title: Maori goddesses in literature. Part 2: 1900-1940

authors: Yates-Smith, Aroha

subjects: Atua wāhine

abstract: Many contemporary Māori are familiar with atua wāhine, Māori goddesses, through accounts that have been passed on to them by word of mouth. Few, however, have had an opportunity to consult accounts of atua wāhine that date from the early period of Māori-Pākehā contact. Those who wish to do so may have considerable difficulty in sifting through all of the written materials for the information they seek. For this reason, this paper provides a review of the literature pertaining to atua wāhine from 1900 to 1940, together with a commentary on the sources to which reference is made. A review of literature on atua wāhine from 1880 – 1900 appeared in the first issue of this Journal. The period 1940 towards 2000 will be reviewed in the next issue.

text: Maori goddesses in literature. Part 2: 1900-1940 Many contemporary Māori are familiar with atua wāhine, Māori goddesses, through accounts that have been passed on to them by word of mouth. Few, however, have had an opportunity to consult accounts of atua wāhine that date from the early period of Māori-Pākehā contact. Those who wish to do so may have considerable difficulty in sifting through all of the written materials for the information they seek. For this reason, this paper provides a review of the literature pertaining to atua wāhine from 1900 to 1940, together with a commentary on the sources to which reference is made. A review of literature on atua wāhine from 1880 – 1900 appeared in the first issue of this Journal. The period 1940 towards 2000 will be reviewed in the next issue.

year: 2001-02