title: Volcanology of the basaltic lava succession within the Auckland pit of the Bombay Quarry, Bombay Volcanic Complex, South Auckland Volcanic Field

authors: Kapasi, Aliasgar

subjects: Volcanology

abstract: The South Auckland Volcanic Field (SAVF), which was active 1.59 – 0.51 million years ago and comprises around 82 volcanic centres, represents a complete history of a monogenetic field preserved in the geological record. The Auckland pit in the Bombay Quarry was recently exposed, revealing an infilled palaeovalley of volcanic and sedimentary deposits possibly associated with the nearby Bombay Volcanic Complex. A set of vertical drill cores from across the quarry were available for this study.
 
The stratigraphy of the volcanic and sedimentary deposits and the facies architecture were examined and described from the drill cores available, and a set of stratigraphic logs were produced. Volcanic and sedimentary units identified were: basement Waitemata and Tauranga group sediments, three individual ponded basalt lavas with intercalated scoria and Quaternary alluvium and/or Kauroa ash deposits. Facies identified include: moderately vesicular basalt (A.1), vesicular basalt with vesicle trails (A.2), non-vesicular basalt (A.3), poorly vesicular basalt (A.4), scoria deposit (B), scoriaceous basalt (C) and intercalated silt/clay (D).

Petrographic characteristics were analysed by optical microscopy, which show that all three basalt lavas have minerals comprising: olivine and clinopyroxene phenocrysts, and a groundmass of plagioclase, opaques and mafic minerals, however, the proportions of each mineral vary between samples. Olivine, clinopyroxene and plagioclase elemental compositions for each of the three basalt units were determined by electron microprobe analysis and revealed that the middle basalt had relatively lower proportion of Mg- and Ca-rich minerals compared to the upper and lower basalts. Furthermore, mineral compositions were consistent with the broad group B rock type of the SAVF lavas.
  
Bulk-rock geochemical characteristics were analysed by X-ray fluorescence spectrometry where the basalt samples were classified as basanites and ne-hawaiites. The lower and upper basalts have a relatively wide range of major and trace element compositions; whereas, the middle basalt has less variation.

The three basalt lava flows represent pahoehoe and/or transitional lava flows, which occurred during magmatic eruptions separated by periods of volcanic quiescence represented by Quaternary alluvium and/or Kauroa ash deposits. The magma source beneath the Bombay area reveals that it consists of dominantly a garnet-bearing peridotite source where only group B type lavas were erupted over time. This process indicates a polygenetic-like eruption history within a monogenetic field, which may be an ideal analogue for understanding the future of shield volcanism in the South Auckland and Auckland Volcanic Field.

text: Volcanology of the basaltic lava succession within the Auckland pit of the Bombay Quarry, Bombay Volcanic Complex, South Auckland Volcanic Field The South Auckland Volcanic Field (SAVF), which was active 1.59 – 0.51 million years ago and comprises around 82 volcanic centres, represents a complete history of a monogenetic field preserved in the geological record. The Auckland pit in the Bombay Quarry was recently exposed, revealing an infilled palaeovalley of volcanic and sedimentary deposits possibly associated with the nearby Bombay Volcanic Complex. A set of vertical drill cores from across the quarry were available for this study.
 
The stratigraphy of the volcanic and sedimentary deposits and the facies architecture were examined and described from the drill cores available, and a set of stratigraphic logs were produced. Volcanic and sedimentary units identified were: basement Waitemata and Tauranga group sediments, three individual ponded basalt lavas with intercalated scoria and Quaternary alluvium and/or Kauroa ash deposits. Facies identified include: moderately vesicular basalt (A.1), vesicular basalt with vesicle trails (A.2), non-vesicular basalt (A.3), poorly vesicular basalt (A.4), scoria deposit (B), scoriaceous basalt (C) and intercalated silt/clay (D).

Petrographic characteristics were analysed by optical microscopy, which show that all three basalt lavas have minerals comprising: olivine and clinopyroxene phenocrysts, and a groundmass of plagioclase, opaques and mafic minerals, however, the proportions of each mineral vary between samples. Olivine, clinopyroxene and plagioclase elemental compositions for each of the three basalt units were determined by electron microprobe analysis and revealed that the middle basalt had relatively lower proportion of Mg- and Ca-rich minerals compared to the upper and lower basalts. Furthermore, mineral compositions were consistent with the broad group B rock type of the SAVF lavas.
  
Bulk-rock geochemical characteristics were analysed by X-ray fluorescence spectrometry where the basalt samples were classified as basanites and ne-hawaiites. The lower and upper basalts have a relatively wide range of major and trace element compositions; whereas, the middle basalt has less variation.

The three basalt lava flows represent pahoehoe and/or transitional lava flows, which occurred during magmatic eruptions separated by periods of volcanic quiescence represented by Quaternary alluvium and/or Kauroa ash deposits. The magma source beneath the Bombay area reveals that it consists of dominantly a garnet-bearing peridotite source where only group B type lavas were erupted over time. This process indicates a polygenetic-like eruption history within a monogenetic field, which may be an ideal analogue for understanding the future of shield volcanism in the South Auckland and Auckland Volcanic Field.

year: 2016

title: Application of lidar techniques to time-of-flight range imaging

authors: Whyte, Refael

subjects: Science & Technology

abstract: Amplitude modulated continuous wave (AMCW) time-of flight (ToF) range imaging cameras measure distance by illuminating the scene with amplitude modulated light and measuring the phase difference between the transmitted and reflected modulation envelope. This method of optical range measurement suffers from errors caused by multiple propagation paths, motion, phase wrapping and non-ideal amplitude modulation. In this paper a ToF camera is modified to operate in modes analogous to continuous wave (CW) and stepped frequency continuous wave (SFCW) lidar. In CW operation the velocity of objects can be measured. CW measurement of velocity was linear with true velocity (R² = 0.9969). Qualitative analysis of a complex scene confirms that range measured by SFCW is resilient to errors caused by multiple propagation paths, phase wrapping and non-ideal amplitude modulation which plague AMCW operation. In viewing a complicated scene through a translucent sheet, quantitative comparison of AMCW with SFCW demonstrated a reduction in the median error from −1.3 m to −0.06 m with inter-quartile range of error reduced from 4.0 m to 0.18 m.

text: Application of lidar techniques to time-of-flight range imaging Amplitude modulated continuous wave (AMCW) time-of flight (ToF) range imaging cameras measure distance by illuminating the scene with amplitude modulated light and measuring the phase difference between the transmitted and reflected modulation envelope. This method of optical range measurement suffers from errors caused by multiple propagation paths, motion, phase wrapping and non-ideal amplitude modulation. In this paper a ToF camera is modified to operate in modes analogous to continuous wave (CW) and stepped frequency continuous wave (SFCW) lidar. In CW operation the velocity of objects can be measured. CW measurement of velocity was linear with true velocity (R² = 0.9969). Qualitative analysis of a complex scene confirms that range measured by SFCW is resilient to errors caused by multiple propagation paths, phase wrapping and non-ideal amplitude modulation which plague AMCW operation. In viewing a complicated scene through a translucent sheet, quantitative comparison of AMCW with SFCW demonstrated a reduction in the median error from −1.3 m to −0.06 m with inter-quartile range of error reduced from 4.0 m to 0.18 m.

year: 2015

title: Data logging and performance analysis software for teachers of indigenous New Zealanders: early results

authors: Barbour, Robert H.

abstract: Technology, in the form of personal computers, is making inroads into everyday life in every part of every nation. It is frequently assumed that this is 'a good thing'. However, there is a need for the people in each cultural group in each nation to appropriate technology for themselves. Indigenous people, such as the Maori of New Zealand/Aotearoa, are in danger of losing their language because technology has a European face. Yet despite the fact that the Maori are currently experiencing a cultural renaissance, there are no commercially available products that are specifically designed for Maori-speaking people.

text: Data logging and performance analysis software for teachers of indigenous New Zealanders: early results Technology, in the form of personal computers, is making inroads into everyday life in every part of every nation. It is frequently assumed that this is 'a good thing'. However, there is a need for the people in each cultural group in each nation to appropriate technology for themselves. Indigenous people, such as the Maori of New Zealand/Aotearoa, are in danger of losing their language because technology has a European face. Yet despite the fact that the Maori are currently experiencing a cultural renaissance, there are no commercially available products that are specifically designed for Maori-speaking people.

year: 1992