title: Geology of the northern Mamaku Plateau

authors: Morgan, Michael Denis

abstract: The geology of the northern Mamaku Plateau is dominated by the rhyolitic Mamaku and Waimakariri lgnimbrites, although exposures of the dacitic Waiteariki Ignimbrite are common in river gorges. 

The Mamaku lgnimbrite comprises 4 flow units (sheets 1 to 4). The base of sheet 2 (the bulk of the ignimbrite) is an uncompacted pyroclastic breccia to lapilli tuff grading into a moderate to strongly welded zone, often lenticulitic. The upper zone is incipiently welded, often light pinkish grey, with poor to moderate crystal contents. Fossil fumeroles are common in the upper middle of the flow, devitrification and vapour phase alteration is extensive. The upper zone of the Waimakariri Ignimbrite is usually light grey and incipiently welded. Towards the lower middle of the flow this grades down into a welded lenticulite, occasionally eutaxitic. The base is usually an incipiently welded pyroclastic breccia enriched in lithics. This ignimbrite has a poor to moderate crystal content, is composed of at least three flow units and often has an underlying Plinian airfall. Gas escape structures appear in distal outcrops.

The unwelded top of the Waiteariki Ignimbrite is often eroded. Usually only the middle of the flow, a densely welded lenticulitic with eutaxitic texture is present. The base of the flow is a moderately devitrified, incipiently welded, pyroclastic breccia to fine tuff. Evidence suggests the Waiteariki Ignimbrite comprises 2 cooling units both of which are crystal rich.

With increasing distance from source plagioclase crystal percentages, pumice size and pumice percentages decrease in the Mamaku Ignimbrite (sheet 2). For the Waimakariri Ignimbrite, there is a decrease in crystal lengths with distance from source (assumed to be the Taupo Volcanic Zone). There is an increase in crystal percentages from a medial to distal position, and a moderate increase in pumice percentages. This is explained by elutruation of vitric material from the Waimakariri as a co-ignimbrite air fall ash concentrating pumice and crystals.

No relationship exists between crystal length and vertical position in the Mamaku ignimbrite. Pumice percentages often increase towards the top of the flow, while pumice numbers increase towards the middle of the flow. Welding is at a minimum at the base, at a maximum in the lower middle of the outcrop, reducing towards the top of the flow. Phenocryst increase towards the base of sheet 2 is attributed to welding/compaction. No relation exists between crystal length and vertical position in the Waimakariri Ignimbrite; pumice percentages and size increase towards the base of the flow, while pumice numbers often increase towards the base and top of the flow. 

Horizontal sections over distances of 194 and 350 m for the Mamaku and Waimakariri Ignimbrites respectively, demonstrated that they are relatively homogeneous over short distances.

Both the Mamaku and Waimakariri Ignimbrites traveled as moderately fluidized laminar flows, but the surge deposits separating Mamaku flow units were turbulent as were parts of distal Waimakariri. The surges (probably foward jetting from the front of the flow) imply the Waimakariri flowed faster than the Mamaku Ignimbrite. A new flow unit is presented, perhaps more applicable to distal large ignimbrite eruptions, than the standard ignimbrite flow unit. Most field evidence indicated the Mamaku and Waimakariri Ignimbrites were emplaced en masse. The diversity of facies in both Mamaku and Waimakariri Ignimbrites implies a single large pyroclastic flow can operate under several flow regimes, dependent to some extent on local paleo-surface conditions.

text: Geology of the northern Mamaku Plateau The geology of the northern Mamaku Plateau is dominated by the rhyolitic Mamaku and Waimakariri lgnimbrites, although exposures of the dacitic Waiteariki Ignimbrite are common in river gorges. 

The Mamaku lgnimbrite comprises 4 flow units (sheets 1 to 4). The base of sheet 2 (the bulk of the ignimbrite) is an uncompacted pyroclastic breccia to lapilli tuff grading into a moderate to strongly welded zone, often lenticulitic. The upper zone is incipiently welded, often light pinkish grey, with poor to moderate crystal contents. Fossil fumeroles are common in the upper middle of the flow, devitrification and vapour phase alteration is extensive. The upper zone of the Waimakariri Ignimbrite is usually light grey and incipiently welded. Towards the lower middle of the flow this grades down into a welded lenticulite, occasionally eutaxitic. The base is usually an incipiently welded pyroclastic breccia enriched in lithics. This ignimbrite has a poor to moderate crystal content, is composed of at least three flow units and often has an underlying Plinian airfall. Gas escape structures appear in distal outcrops.

The unwelded top of the Waiteariki Ignimbrite is often eroded. Usually only the middle of the flow, a densely welded lenticulitic with eutaxitic texture is present. The base of the flow is a moderately devitrified, incipiently welded, pyroclastic breccia to fine tuff. Evidence suggests the Waiteariki Ignimbrite comprises 2 cooling units both of which are crystal rich.

With increasing distance from source plagioclase crystal percentages, pumice size and pumice percentages decrease in the Mamaku Ignimbrite (sheet 2). For the Waimakariri Ignimbrite, there is a decrease in crystal lengths with distance from source (assumed to be the Taupo Volcanic Zone). There is an increase in crystal percentages from a medial to distal position, and a moderate increase in pumice percentages. This is explained by elutruation of vitric material from the Waimakariri as a co-ignimbrite air fall ash concentrating pumice and crystals.

No relationship exists between crystal length and vertical position in the Mamaku ignimbrite. Pumice percentages often increase towards the top of the flow, while pumice numbers increase towards the middle of the flow. Welding is at a minimum at the base, at a maximum in the lower middle of the outcrop, reducing towards the top of the flow. Phenocryst increase towards the base of sheet 2 is attributed to welding/compaction. No relation exists between crystal length and vertical position in the Waimakariri Ignimbrite; pumice percentages and size increase towards the base of the flow, while pumice numbers often increase towards the base and top of the flow. 

Horizontal sections over distances of 194 and 350 m for the Mamaku and Waimakariri Ignimbrites respectively, demonstrated that they are relatively homogeneous over short distances.

Both the Mamaku and Waimakariri Ignimbrites traveled as moderately fluidized laminar flows, but the surge deposits separating Mamaku flow units were turbulent as were parts of distal Waimakariri. The surges (probably foward jetting from the front of the flow) imply the Waimakariri flowed faster than the Mamaku Ignimbrite. A new flow unit is presented, perhaps more applicable to distal large ignimbrite eruptions, than the standard ignimbrite flow unit. Most field evidence indicated the Mamaku and Waimakariri Ignimbrites were emplaced en masse. The diversity of facies in both Mamaku and Waimakariri Ignimbrites implies a single large pyroclastic flow can operate under several flow regimes, dependent to some extent on local paleo-surface conditions.

year: 1986

title: The Solution to the problem of the individuation of actions

authors: Jones, Donald Robert

abstract: How many possible answers are there to the problem of the individuation of actions? In this dissertation I shall confine myself to but two answers. I will not state categorically that there are no other lines of approach to the problem. I am, however, reasonably confident that no other line is at all feasible and that no one has formulated one. There is the possibility of blending the two answers with which I shall deal, but such a blending would at best be mere temporising. It should become obvious that the two answers are mutually antagonistic and that no such blending could be convincingly defended.

text: The Solution to the problem of the individuation of actions How many possible answers are there to the problem of the individuation of actions? In this dissertation I shall confine myself to but two answers. I will not state categorically that there are no other lines of approach to the problem. I am, however, reasonably confident that no other line is at all feasible and that no one has formulated one. There is the possibility of blending the two answers with which I shall deal, but such a blending would at best be mere temporising. It should become obvious that the two answers are mutually antagonistic and that no such blending could be convincingly defended.

year: 1973

title: A core phyllosphere microbiome exists across distant populations of a tree species indigenous to New Zealand

authors: Noble, Anya S.

subjects: Science & Technology

abstract: The phyllosphere microbiome is increasingly recognised as an influential component of plant physiology, yet it remains unclear whether stable host-microbe associations generally exist in the phyllosphere. Leptospermum scoparium (mānuka) is a tea tree indigenous to New Zealand, and honey derived from mānuka is widely known to possess unique antimicrobial properties. However, the host physiological traits associated with these antimicrobial properties vary widely, and the specific cause of such variation has eluded scientists despite decades of research. Notably, the mānuka phyllosphere microbiome remains uncharacterised, and its potential role in mediating host physiology has not been considered. Working within the prevailing core microbiome conceptual framework, we hypothesise that the phyllosphere microbiome of mānuka exhibits specific host association patterns congruent with those of a microbial community under host selective pressure (null hypothesis: the mānuka phyllosphere microbiome is recruited stochastically from the surrounding environment). To examine our hypothesis, we characterised the phyllosphere and associated soil microbiomes of five distinct and geographically distant mānuka populations across the North Island of New Zealand. We identified a habitat-specific and relatively abundant core microbiome in the mānuka phyllosphere, which was persistent across all samples. In contrast, non-core phyllosphere microorganisms exhibited significant variation across individual host trees and populations that was strongly driven by environmental and spatial factors. Our results demonstrate the existence of a dominant and ubiquitous core microbiome in the phyllosphere of mānuka, supporting our hypothesis that phyllosphere microorganisms of mānuka exhibit specific host association and potentially mediate physiological traits of this nationally and culturally treasured indigenous plant. In addition, our results illustrate biogeographical patterns in mānuka phyllosphere microbiomes and offer insight into factors contributing to phyllosphere microbiome assembly.

text: A core phyllosphere microbiome exists across distant populations of a tree species indigenous to New Zealand The phyllosphere microbiome is increasingly recognised as an influential component of plant physiology, yet it remains unclear whether stable host-microbe associations generally exist in the phyllosphere. Leptospermum scoparium (mānuka) is a tea tree indigenous to New Zealand, and honey derived from mānuka is widely known to possess unique antimicrobial properties. However, the host physiological traits associated with these antimicrobial properties vary widely, and the specific cause of such variation has eluded scientists despite decades of research. Notably, the mānuka phyllosphere microbiome remains uncharacterised, and its potential role in mediating host physiology has not been considered. Working within the prevailing core microbiome conceptual framework, we hypothesise that the phyllosphere microbiome of mānuka exhibits specific host association patterns congruent with those of a microbial community under host selective pressure (null hypothesis: the mānuka phyllosphere microbiome is recruited stochastically from the surrounding environment). To examine our hypothesis, we characterised the phyllosphere and associated soil microbiomes of five distinct and geographically distant mānuka populations across the North Island of New Zealand. We identified a habitat-specific and relatively abundant core microbiome in the mānuka phyllosphere, which was persistent across all samples. In contrast, non-core phyllosphere microorganisms exhibited significant variation across individual host trees and populations that was strongly driven by environmental and spatial factors. Our results demonstrate the existence of a dominant and ubiquitous core microbiome in the phyllosphere of mānuka, supporting our hypothesis that phyllosphere microorganisms of mānuka exhibit specific host association and potentially mediate physiological traits of this nationally and culturally treasured indigenous plant. In addition, our results illustrate biogeographical patterns in mānuka phyllosphere microbiomes and offer insight into factors contributing to phyllosphere microbiome assembly.

year: 2020