title: Characteristics and origin of hydrothermal pebble dykes and associated host rock alteration on the Thames coast, Coromandel Volcanic Zone

authors: Harvey-Wishart, Holly

abstract: During the Miocene to early Pliocene (c. 18 Ma to 2 Ma), subduction-related  volcanism migrated down the Coromandel Peninsula forming the Coromandel  Volcanic Zone. This period resulted in the development of extensive  hydrothermal systems which interacted with the associated volcanic sequences, the Coromandel Group andesites and dacites. As well as introducing extensive alteration and epithermal Au-Ag deposits, the active environment resulted in the emplacement of co-hydrothermal pebble dyke units. Examples of these features have been identified on the Coromandel west coast, exposed as bodies of fractured rock material, hosting well-rounded clasts due to milling during transport forming “pebbles”. This material has been incorporated from a variety of lithologies from different stratigraphic depths, providing a ground surface expression of the subsurface. As the formation of these dykes is not well defined, whether they are a result of volcanic or hydrothermal activity, this study aims to investigate their origin and the influence they may have had on the character of proximal hydrothermal alteration.  

A combination of field descriptions, optical petrology, SEM, XRD, XRF and ICP-MS geochemistry was all involved in investigating the study site along the Thames coastline, where two clusters of dykes are exposed within a ~ 600 m span of beach. The local hydrothermal character was determined from the mineralogy, reflective of the fluids and physical conditions involved in the mineralization of altered products. The extent of the site hosts multiple alteration zones, recognised as propylitic and phyllic alteration associated with periods of mineralisation, and supergene argillic overprinting.  The gangue mineralogy also mirrors the character of the broader system, reflecting near-neutral fluids associated with the low-sulfidation epithermal environment at temperatures of  ~ 240 – 260 °C. 

To understand the role of the pebble dykes within this setting and the origin of their deposits, identifying the mechanisms involved in their formation is crucial. Characteristics of dyke morphologies, clast lithologies and morphologies, and  alteration character suggest fluidisation played a large role, particularly so in the 
transport of fragmented rock material from depth. The extent of their ascent is best reflected by the occurrences of greywacke argillite and sandstone components found in each of the exposures. These lithologies are sourced from the Manaia Hill group of the Waipapa Terrane, a deep basement unit recognised  as the basement rock of New Zealand. Therefore, the presence of greywacke and argillite clasts suggest possible significant depths of material transport and the interaction with high volumes of hydrothermal solutions. However, due to the alteration style and morphologies of the clasts, it is also possible they were instead fragmented at similar depths to the shallower local volcanic stratigraphy.  If pebble dykes were to act as permeable pathways for ore-bearing solutions within a hydrothermal system, it is possible they could play a significant role in the concentration of metals in economically viable quantities. Therefore, under the right circumstances; emplacement during or pre-mineralisation, orientated preferential to fluid flow direction and hosted within otherwise impermeable host rock, they could yet act as a vector towards potential mineralisation.

text: Characteristics and origin of hydrothermal pebble dykes and associated host rock alteration on the Thames coast, Coromandel Volcanic Zone During the Miocene to early Pliocene (c. 18 Ma to 2 Ma), subduction-related  volcanism migrated down the Coromandel Peninsula forming the Coromandel  Volcanic Zone. This period resulted in the development of extensive  hydrothermal systems which interacted with the associated volcanic sequences, the Coromandel Group andesites and dacites. As well as introducing extensive alteration and epithermal Au-Ag deposits, the active environment resulted in the emplacement of co-hydrothermal pebble dyke units. Examples of these features have been identified on the Coromandel west coast, exposed as bodies of fractured rock material, hosting well-rounded clasts due to milling during transport forming “pebbles”. This material has been incorporated from a variety of lithologies from different stratigraphic depths, providing a ground surface expression of the subsurface. As the formation of these dykes is not well defined, whether they are a result of volcanic or hydrothermal activity, this study aims to investigate their origin and the influence they may have had on the character of proximal hydrothermal alteration.  

A combination of field descriptions, optical petrology, SEM, XRD, XRF and ICP-MS geochemistry was all involved in investigating the study site along the Thames coastline, where two clusters of dykes are exposed within a ~ 600 m span of beach. The local hydrothermal character was determined from the mineralogy, reflective of the fluids and physical conditions involved in the mineralization of altered products. The extent of the site hosts multiple alteration zones, recognised as propylitic and phyllic alteration associated with periods of mineralisation, and supergene argillic overprinting.  The gangue mineralogy also mirrors the character of the broader system, reflecting near-neutral fluids associated with the low-sulfidation epithermal environment at temperatures of  ~ 240 – 260 °C. 

To understand the role of the pebble dykes within this setting and the origin of their deposits, identifying the mechanisms involved in their formation is crucial. Characteristics of dyke morphologies, clast lithologies and morphologies, and  alteration character suggest fluidisation played a large role, particularly so in the 
transport of fragmented rock material from depth. The extent of their ascent is best reflected by the occurrences of greywacke argillite and sandstone components found in each of the exposures. These lithologies are sourced from the Manaia Hill group of the Waipapa Terrane, a deep basement unit recognised  as the basement rock of New Zealand. Therefore, the presence of greywacke and argillite clasts suggest possible significant depths of material transport and the interaction with high volumes of hydrothermal solutions. However, due to the alteration style and morphologies of the clasts, it is also possible they were instead fragmented at similar depths to the shallower local volcanic stratigraphy.  If pebble dykes were to act as permeable pathways for ore-bearing solutions within a hydrothermal system, it is possible they could play a significant role in the concentration of metals in economically viable quantities. Therefore, under the right circumstances; emplacement during or pre-mineralisation, orientated preferential to fluid flow direction and hosted within otherwise impermeable host rock, they could yet act as a vector towards potential mineralisation.

year: 2020

title: Dating the emergence of the divaricate habit in the New Zealand flora

authors: Maurin, Kévin Jean Louis

subjects: Botany

abstract: The New Zealand divaricates are a collection of shrubs, short trees and tree juveniles whose crowns are made of tough interlaced twigs branching at wide angles and bearing small leaves. These species represent c. 13% of the native woody flora, a proportion not seen in any other region of the world. Since the late 19ᵗʰ century, ecologists and botanists have sought to understand the of drivers this unique case of convergent evolution. Debate has been dominated by two main competing hypotheses invoking (1) the effect of browsing by now-extinct avian herbivores (moa) and (2) a response to frosty and droughty Plio-Pleistocene climates. Observational and experimental evidence, as well as theoretical discussions, have not clearly favoured one over the other. More recently, a synthetic hypothesis involving both climate and browsing has been proposed, but has not been specifically tested yet: the divaricate habit did not become advantageous as an anti-browsing defence until Plio-Pleistocene climatic constraints prevented young trees and shrubs from growing quickly out of reach of ground-dwelling herbivores.
These hypotheses imply different expected divergence periods between divaricate species and their non-divaricate relatives. The focus of this PhD project is to produce a dated phylogeny including as many divaricates as possible, with the aim of bringing new evidence to help tease apart the various hypotheses about their evolution.
This PhD thesis is built from a previously published paper and draft manuscripts intended for submission to scientific journals. The first two papers report phylogenies of small genera (Pennantia J.R.Forst. & G.Forst. and Corokia A.Cunn.) that include divaricate species. These studies helped develop lab methods and offered the opportunity to test diverse phylogenetic methods on a smaller scale in preparation for the third paper, which is the core dating work of this PhD.
The phylogenies of Pennantia and Corokia provided in this thesis (Chapter 2 and 3, respectively) are the first published dated phylogenies of all the species of each genus. Building the phylogeny of Corokia was also the occasion to discuss two theories trying to explain the distribution of extant species on landmasses formerly part of Gondwana: vicariance and long-distance dispersal—Corokia appears to be one of an increasing number of cases where long-distance dispersal is indicated. The dated phylogeny of most New Zealand divaricate species presented in Chapter 4 reveals that, in the great majority of genera with divaricate representatives, the divaricate habit appeared in New Zealand within the last 5 My, i.e. since the beginning of the Pliocene. 
On one hand, this research constitutes a valuable methodological addition to the field of molecular phylogenetics by (1) disseminating a method for retrieving extra genetic markers, at no marginal cost, from Next Generation Sequencing shotgun sequencing data of DNA samples enriched for a specific set of markers, and (2) developing a guide to using a piece of phylogenetic reconstruction software (treePL), which was missing from the literature and needed by users. On the other hand, dating the emergence of the divaricate habit brought new and crucial evidence to the debate over what promoted the evolution of the divaricate habit in New Zealand: the findings are clearly consistent with a major effect of Plio-Pleistocene climates—and given evidence and discussion from past studies of these plants and similar plants around the world, the effect of browsing by moa was also probably involved.

text: Dating the emergence of the divaricate habit in the New Zealand flora The New Zealand divaricates are a collection of shrubs, short trees and tree juveniles whose crowns are made of tough interlaced twigs branching at wide angles and bearing small leaves. These species represent c. 13% of the native woody flora, a proportion not seen in any other region of the world. Since the late 19ᵗʰ century, ecologists and botanists have sought to understand the of drivers this unique case of convergent evolution. Debate has been dominated by two main competing hypotheses invoking (1) the effect of browsing by now-extinct avian herbivores (moa) and (2) a response to frosty and droughty Plio-Pleistocene climates. Observational and experimental evidence, as well as theoretical discussions, have not clearly favoured one over the other. More recently, a synthetic hypothesis involving both climate and browsing has been proposed, but has not been specifically tested yet: the divaricate habit did not become advantageous as an anti-browsing defence until Plio-Pleistocene climatic constraints prevented young trees and shrubs from growing quickly out of reach of ground-dwelling herbivores.
These hypotheses imply different expected divergence periods between divaricate species and their non-divaricate relatives. The focus of this PhD project is to produce a dated phylogeny including as many divaricates as possible, with the aim of bringing new evidence to help tease apart the various hypotheses about their evolution.
This PhD thesis is built from a previously published paper and draft manuscripts intended for submission to scientific journals. The first two papers report phylogenies of small genera (Pennantia J.R.Forst. & G.Forst. and Corokia A.Cunn.) that include divaricate species. These studies helped develop lab methods and offered the opportunity to test diverse phylogenetic methods on a smaller scale in preparation for the third paper, which is the core dating work of this PhD.
The phylogenies of Pennantia and Corokia provided in this thesis (Chapter 2 and 3, respectively) are the first published dated phylogenies of all the species of each genus. Building the phylogeny of Corokia was also the occasion to discuss two theories trying to explain the distribution of extant species on landmasses formerly part of Gondwana: vicariance and long-distance dispersal—Corokia appears to be one of an increasing number of cases where long-distance dispersal is indicated. The dated phylogeny of most New Zealand divaricate species presented in Chapter 4 reveals that, in the great majority of genera with divaricate representatives, the divaricate habit appeared in New Zealand within the last 5 My, i.e. since the beginning of the Pliocene. 
On one hand, this research constitutes a valuable methodological addition to the field of molecular phylogenetics by (1) disseminating a method for retrieving extra genetic markers, at no marginal cost, from Next Generation Sequencing shotgun sequencing data of DNA samples enriched for a specific set of markers, and (2) developing a guide to using a piece of phylogenetic reconstruction software (treePL), which was missing from the literature and needed by users. On the other hand, dating the emergence of the divaricate habit brought new and crucial evidence to the debate over what promoted the evolution of the divaricate habit in New Zealand: the findings are clearly consistent with a major effect of Plio-Pleistocene climates—and given evidence and discussion from past studies of these plants and similar plants around the world, the effect of browsing by moa was also probably involved.

year: 2021

title: E tama Hikairo

authors: Maxwell, Te Kahautu

subjects: Oriori

abstract: He oriori tēnei mō Hikairo, te mokopuna tuatahi a Kīngi Tūheitia. He oriori tēnei e whakanui ana i a Hikairo, tōna whakapapa, tōna tūranga i te ao Māori me te ao Kīngitanga. He mokopuna Ringatū anō a Hikairo, nā Kīngi Tūheitia i tuku mai a Hikairo kia tūātia e Te Hāhi Ringatū ki te Poukai o Wāhi Pā i te tuawaru o Whiringa-ā-Nuku 2014. Ka whakaaturia tōna whakapono Hāhi Ringatū ki roto i te oriori nei e kupu whakaaritia ana. I tohua hoki e Kīngi Tūheitia a Te Kāhautu hai pou whakaruruhau1 mō Hikairo koinei ia i titoa ai tēnei oriori mō tana tamaiti mokopuna, mō Hikairo. He aroha nui nō te matua mō wai oti, mō Hikairo.

I titoa tēnei oriori hai waiatatanga mā te kapa haka o Ōpōtiki Mai Tawhiti. I waiatatia e Ōpōtiki Mai Tawhiti tēnei ki Te Matatini i tū ki Ōtautahi te tau rua mano tekau mā rima. He huarahi anō tēnei mā Te Kāhautu ki te whakamānawa i tana mokopuna i a Hikairo, nara nā te kapa haka a Te Kāhautu i waiata, i whakanui a Hikairo ki te maraenui o te iwi Māori, ko Te Matatini. Ana i tuatahi a Hikairo i te wehenga o Te Waiata Tira. “E Tama Hikairo, haere mai rā.”

text: E tama Hikairo He oriori tēnei mō Hikairo, te mokopuna tuatahi a Kīngi Tūheitia. He oriori tēnei e whakanui ana i a Hikairo, tōna whakapapa, tōna tūranga i te ao Māori me te ao Kīngitanga. He mokopuna Ringatū anō a Hikairo, nā Kīngi Tūheitia i tuku mai a Hikairo kia tūātia e Te Hāhi Ringatū ki te Poukai o Wāhi Pā i te tuawaru o Whiringa-ā-Nuku 2014. Ka whakaaturia tōna whakapono Hāhi Ringatū ki roto i te oriori nei e kupu whakaaritia ana. I tohua hoki e Kīngi Tūheitia a Te Kāhautu hai pou whakaruruhau1 mō Hikairo koinei ia i titoa ai tēnei oriori mō tana tamaiti mokopuna, mō Hikairo. He aroha nui nō te matua mō wai oti, mō Hikairo.

I titoa tēnei oriori hai waiatatanga mā te kapa haka o Ōpōtiki Mai Tawhiti. I waiatatia e Ōpōtiki Mai Tawhiti tēnei ki Te Matatini i tū ki Ōtautahi te tau rua mano tekau mā rima. He huarahi anō tēnei mā Te Kāhautu ki te whakamānawa i tana mokopuna i a Hikairo, nara nā te kapa haka a Te Kāhautu i waiata, i whakanui a Hikairo ki te maraenui o te iwi Māori, ko Te Matatini. Ana i tuatahi a Hikairo i te wehenga o Te Waiata Tira. “E Tama Hikairo, haere mai rā.”

year: 2016