title: Using a tephrostratigraphic framework to determine the past 40,000 yrs of fault rupture and paleohydrothermal activity on the east strand of the Whirinaki Fault, Ngakuru Graben, central Taupo Volcanic Zone

authors: Loame, Remedy Charlotte

subjects: seismology

abstract: The Ngakuru Graben in the central Taupo Volcanic Zone, North Island, New Zealand, is largely thermally inactive, but several fossil geothermal systems have been mapped throughout the area parallel to the Whirinaki Fault (WF). A fossil geothermal system was identified on the northeast section of the east strand of the WF at a location on Hossack Road hereafter referred to as the Meade-Hossack site. The aim of this study was to establish a history of fault rupture and sinter development at the Meade-Hossack site, and to relate the observed faulting and paleogeothermal activity to that at other locations on the WF. The objectives were to (i) describe the stratigraphy exposed in a trench and outcrop, (ii) identify (correlate) tephras using stratigraphic principles, ferromagnesian mineralogical assemblages, and electron microprobe-determined major-element compositions of glass shards, and (iii) restore tectonic deformation at the site using tephrochronology to date the timing of fault movement and the development of sinter formation.

A paleoseismic trench was excavated across the northeast section of the east strand of the WF. The stratigraphy and deformation in the trench were logged. Samples of tephras were taken for mineral and glass shard analysis by microscope petrography and electron microprobe analysis, respectively. Eight tephras were identified, namely the Kaharoa (AD 1314 ± 12 or 636 ± 12 cal. yr. BP) (95% probability age range), Taupo (AD 232 ± 10 or 1718 ± 10 cal. yr. BP), Rotoma (9423 ± 120 cal. yr. BP), Rotorua (15635 ± 412 cal. yr. BP), Okareka (21858 ± 290 cal. yr. BP), Kawakawa (25358 ± 162 cal. yr. BP), Poihipi (28446 ± 670 cal. yr. BP), and Tahuna (c. 40 ka), as well as the Ohakuri Ignimbrite (c. 240 ka).

Five fault rupture events were identified in the trench (MH1–5). The trench logs were used to reconstruct earlier stages of the stratigraphic succession at the site prior to deformation by each rupture events. The tephra ages were used to constrain the timing of fault movement. The slip rates and the vertical displacement measurements were also calculated using tephrochronology, and correlated with trends (fast-slow-fast) for events of similar ages observed in other trenches on the WF.

Rupture event MH1 occurred between the Taupo and Kaharoa eruption episodes at a slip rate of 0.87 ± 0.37 mm/yr, MH2 between the Rotoma and Taupo eruptions at a rate of 0.11 ± 0.20 mm/yr, MH3 between the Rotorua and Rotoma eruptions at a rate of 0.20 ± 0.22 mm/yr, MH4 between the Okareka and Rotorua eruptions at a rate of 0.13 ± 0.27 mm/yr, and MH5 between the Ohakuri and Okareka eruptions at a rate of 0.53 ± 0.24 mm/yr. The recurrence interval during the last 21.8 kyrs was calculated to be 1.8–5.4 kyrs, which fits within recurrence intervals calculated for other trenches on the WF.

The rupture events at the Meade-Hossack site show evidence of stress transfer from the southeast section of the east strand as well as the northwest section of the west strand of the WF, indicating that the strands are connected at depth. Sinter deposition mirrors that on the west strand from ~40–10 ka, indicating that the paleogeothermal fields were fed by the same source at depth.Sinter deposition mirrors that on the west strand from ~40–10 ka, indicating that the paleogeothermal fields were fed by the same source at depth. Fault rupture MH3 at the Meade-Hossack site altered the local fluid flow regime, leading to the cessation of sinter development on the east strand by 9423 ± 120 cal. yr. BP.

text: Using a tephrostratigraphic framework to determine the past 40,000 yrs of fault rupture and paleohydrothermal activity on the east strand of the Whirinaki Fault, Ngakuru Graben, central Taupo Volcanic Zone The Ngakuru Graben in the central Taupo Volcanic Zone, North Island, New Zealand, is largely thermally inactive, but several fossil geothermal systems have been mapped throughout the area parallel to the Whirinaki Fault (WF). A fossil geothermal system was identified on the northeast section of the east strand of the WF at a location on Hossack Road hereafter referred to as the Meade-Hossack site. The aim of this study was to establish a history of fault rupture and sinter development at the Meade-Hossack site, and to relate the observed faulting and paleogeothermal activity to that at other locations on the WF. The objectives were to (i) describe the stratigraphy exposed in a trench and outcrop, (ii) identify (correlate) tephras using stratigraphic principles, ferromagnesian mineralogical assemblages, and electron microprobe-determined major-element compositions of glass shards, and (iii) restore tectonic deformation at the site using tephrochronology to date the timing of fault movement and the development of sinter formation.

A paleoseismic trench was excavated across the northeast section of the east strand of the WF. The stratigraphy and deformation in the trench were logged. Samples of tephras were taken for mineral and glass shard analysis by microscope petrography and electron microprobe analysis, respectively. Eight tephras were identified, namely the Kaharoa (AD 1314 ± 12 or 636 ± 12 cal. yr. BP) (95% probability age range), Taupo (AD 232 ± 10 or 1718 ± 10 cal. yr. BP), Rotoma (9423 ± 120 cal. yr. BP), Rotorua (15635 ± 412 cal. yr. BP), Okareka (21858 ± 290 cal. yr. BP), Kawakawa (25358 ± 162 cal. yr. BP), Poihipi (28446 ± 670 cal. yr. BP), and Tahuna (c. 40 ka), as well as the Ohakuri Ignimbrite (c. 240 ka).

Five fault rupture events were identified in the trench (MH1–5). The trench logs were used to reconstruct earlier stages of the stratigraphic succession at the site prior to deformation by each rupture events. The tephra ages were used to constrain the timing of fault movement. The slip rates and the vertical displacement measurements were also calculated using tephrochronology, and correlated with trends (fast-slow-fast) for events of similar ages observed in other trenches on the WF.

Rupture event MH1 occurred between the Taupo and Kaharoa eruption episodes at a slip rate of 0.87 ± 0.37 mm/yr, MH2 between the Rotoma and Taupo eruptions at a rate of 0.11 ± 0.20 mm/yr, MH3 between the Rotorua and Rotoma eruptions at a rate of 0.20 ± 0.22 mm/yr, MH4 between the Okareka and Rotorua eruptions at a rate of 0.13 ± 0.27 mm/yr, and MH5 between the Ohakuri and Okareka eruptions at a rate of 0.53 ± 0.24 mm/yr. The recurrence interval during the last 21.8 kyrs was calculated to be 1.8–5.4 kyrs, which fits within recurrence intervals calculated for other trenches on the WF.

The rupture events at the Meade-Hossack site show evidence of stress transfer from the southeast section of the east strand as well as the northwest section of the west strand of the WF, indicating that the strands are connected at depth. Sinter deposition mirrors that on the west strand from ~40–10 ka, indicating that the paleogeothermal fields were fed by the same source at depth.Sinter deposition mirrors that on the west strand from ~40–10 ka, indicating that the paleogeothermal fields were fed by the same source at depth. Fault rupture MH3 at the Meade-Hossack site altered the local fluid flow regime, leading to the cessation of sinter development on the east strand by 9423 ± 120 cal. yr. BP.

year: 2016

title: Plasticization of Bloodmeal-based Thermoplastics

authors: Verbeek, Casparus Johan R.

abstract: Water is the most common plasticizer for proteinbased thermoplastics, lowering the softening point to a allow processing without excessive degradation. The biggest drawback of using water a plasticizer is that water easily evaporates from the material during use or storage. This leads to embrittlement and loss of functionality over time. In this study a series of high molecular mass plasticizers were evaluated for their efficiency in plasticizing bloodmeal-based thermoplastics. It was found that propylene glycol, di and tri-ethylene glycol were most efficient in increasing the material’s ductility, as measured by elongation at break. Using 10 parts plasticizer per hundred bloodmeal (pphBM) in combination with 10 pphBM urea gave optimal results in terms of Young’s modulus, tensile strength and processability. The mechanical properties of plasticized samples showed a stronger dependency on moisture content, compared to unplasticized samples and reached higher equilibrium moisture content in a shorter time. Using 10 pphBM TEG as plasticizer in resulted in a plastic material with a Young’s modulus of 869 MPa, tensile strength of 14.7 MPa and an elongation at break of 46%.

text: Plasticization of Bloodmeal-based Thermoplastics Water is the most common plasticizer for proteinbased thermoplastics, lowering the softening point to a allow processing without excessive degradation. The biggest drawback of using water a plasticizer is that water easily evaporates from the material during use or storage. This leads to embrittlement and loss of functionality over time. In this study a series of high molecular mass plasticizers were evaluated for their efficiency in plasticizing bloodmeal-based thermoplastics. It was found that propylene glycol, di and tri-ethylene glycol were most efficient in increasing the material’s ductility, as measured by elongation at break. Using 10 parts plasticizer per hundred bloodmeal (pphBM) in combination with 10 pphBM urea gave optimal results in terms of Young’s modulus, tensile strength and processability. The mechanical properties of plasticized samples showed a stronger dependency on moisture content, compared to unplasticized samples and reached higher equilibrium moisture content in a shorter time. Using 10 pphBM TEG as plasticizer in resulted in a plastic material with a Young’s modulus of 869 MPa, tensile strength of 14.7 MPa and an elongation at break of 46%.

year: 2013

title: Moving away from home: Some social consequences for Tūhoe migrating to the Waikato

authors: Nikora, Linda Waimarie

subjects: psychology

abstract: To better understand the social consequences of migration away from traditional iwi regions, Tūhoe researchers intensively interviewed 40 Tūhoe people who had moved to the Waikato. It was found that most missed whanau and the community and made regular visits back home. Participants reported utilizing extensive whanau links to set themselves up in the Waikato, and many joined the Tūhoe associations in the Waikato. Others who did not join reported liking the idea that Tūhoe were there if needed. Some participants felt stronger in their Tūhoe identity since moving, and most reported noticing changes occurring in themselves or those back home over this period (they felt more worldly but saw those back home as more insular). While they did not interact much with tangata whenua, or participate in tangata whenua events, many said that they had a better appreciation of the local Tainui and the Kīngitanga groups since migrating. Finally, most would like to return to their iwi region for employment if it were available but saw little chance of this happening, and most reported wanting to retire there. The policy implications of both these points are explored.

text: Moving away from home: Some social consequences for Tūhoe migrating to the Waikato To better understand the social consequences of migration away from traditional iwi regions, Tūhoe researchers intensively interviewed 40 Tūhoe people who had moved to the Waikato. It was found that most missed whanau and the community and made regular visits back home. Participants reported utilizing extensive whanau links to set themselves up in the Waikato, and many joined the Tūhoe associations in the Waikato. Others who did not join reported liking the idea that Tūhoe were there if needed. Some participants felt stronger in their Tūhoe identity since moving, and most reported noticing changes occurring in themselves or those back home over this period (they felt more worldly but saw those back home as more insular). While they did not interact much with tangata whenua, or participate in tangata whenua events, many said that they had a better appreciation of the local Tainui and the Kīngitanga groups since migrating. Finally, most would like to return to their iwi region for employment if it were available but saw little chance of this happening, and most reported wanting to retire there. The policy implications of both these points are explored.

year: 2004