scholarly journals Structural Controls on Shallow Cenozoic Fluid Flow in the Otago Schist, New Zealand

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-25
Author(s):  
Simon C. Holbek ◽  
Madison Frank ◽  
James M. Scott ◽  
Steven A. F. Smith ◽  
Petrus J. le Roux ◽  
...  
Keyword(s):  
Fluid Flow ◽  
New Zealand ◽  
Hydrothermal Systems ◽  
Strike Slip ◽  
Geochemical Data ◽  
Small Displacement ◽  
Type I ◽  
The South ◽  
Vein Formation ◽  
Otago Schist

The Otago Schist in the South Island of New Zealand represents an exhumed Mesozoic accretionary prism. Two coastal areas (Akatore Creek and Bruce Rocks) south of Dunedin preserve structural and geochemical evidence for the development of postmetamorphic hydrothermal systems that involved widespread fluid-rock reaction at shallow crustal depths. The Jurassic to Triassic pumpellyite-actinolite (Akatore Creek) to upper greenschist facies (Bruce Rocks) metamorphic fabrics were crosscut by sets of regionally extensive Cretaceous exhumation joints. Many of the joints were subsequently reactivated to form networks of small-displacement (<metres) strike-slip faults containing cemented fault breccias and veins composed of hydrothermal calcite, siderite, and ankerite. Paleostress analysis performed on infrequent fault slickenlines indicates an overall strike-slip paleostress regime and a paleo-σ1 orientation (azimuth 094°) similar to the contemporary σ1 orientation in Otago and Canterbury (azimuth c. 110°-120°). High δ18O values in vein calcite (δ18OVPDB=21 to 28‰), together with the predominance of Type I calcite twins, suggest that vein formation occurred at low temperatures (<200°C) in the shallow crust and was associated with strongly channelized fluid flow along the joint and fault networks. Mass-balance calculations performed on samples from carbonate alteration zones show that significant mobilisation of elements occurred during fluid flow and fluid-rock reaction. Whole-rock and in situ carbonate 87Sr/86Sr data indicate varying degrees of interaction between the hydrothermal fluids and the host rock schists. Fluids were likely derived from the breakdown of metamorphic Ca-rich mineral phases with low 87Rb in the host schists (e.g., epidote or calcite), as well as more radiogenic components such as mica. Overall, the field and geochemical data suggest that shallow fluid flow in the field areas was channelized along foliation surfaces, exhumation joints, and networks of brittle faults, and that these structures controlled the distribution of fluid-rock reactions and hydrothermal veins. The brittle fault networks and associated hydrothermal systems are interpreted to have formed after the onset of Early Miocene compression in the South Island and may represent the manifestation of fracturing and fluid flow associated with reverse reactivation of regional-scale faults such as the nearby Akatore Fault.

scholarly journals Self-Potential Studies in Volcanic Environments: A Cheap and Efficient Method for Multiscale Fluid-Flow Investigations

2019 ◽  
Vol 2019 ◽  
pp. 1-19 ◽  
Author(s):  
N. Grobbe ◽  
S. Barde-Cabusson
Keyword(s):  
Electrical Resistivity ◽  
Fluid Flow ◽  
Case Studies ◽  
Potential Method ◽  
Hydrothermal Systems ◽  
Geochemical Data ◽  
Data Types ◽  
Spatial And Temporal Scales ◽  
Cooling Behavior ◽  
Self Potential

We demonstrate the value of using the self-potential method to study volcanic environments, and particularly fluid flow in those environments. We showcase the fact that self-potential measurements are a highly efficient way to map large areas of volcanic systems under challenging terrain conditions, where other geophysical techniques may be challenging or expensive to deploy. Using case studies of a variety of volcano types, including tuff cones, shield volcanoes, stratovolcanoes, and monogenetic fields, we emphasize the fact that self-potential signals enable us to study fluid flow in volcanic settings on multiple spatial and temporal scales. We categorize the examples into the following three multiscale fluid-flow processes: (1) deep hydrothermal systems, (2) shallow hydrothermal systems, and (3) groundwater. These examples highlight the different hydrological, hydrothermal, and structural inferences that can be made from self-potential signals, such as insight into shallow and deep hydrothermal systems, cooling behavior of lava flows, different hydrogeological domains, upwelling, infiltration, and lateral groundwater and hydrothermal fluid flow paths and velocities, elevation of the groundwater level, crater limits, regional faults, rift zones, incipient collapse limits, structural domains, and buried calderas. The case studies presented in this paper clearly demonstrate that the measured SP signals are a result of the coplay between microscale processes (e.g., electrokinetic, thermoelectric) and macroscale structural and environmental features. We discuss potential challenges and their causes when trying to uniquely interpret self-potential signals. Through integration with different geophysical and geochemical data types such as subsurface electrical resistivity distributions obtained from, e.g., electrical resistivity tomography or magnetotellurics, soil CO2 flux, and soil temperature, it is demonstrated that the hydrogeological interpretations obtained from SP measurements can be better constrained and/or validated.

scholarly journals Strike-Slip Enables Subduction Initiation Beneath a Failed Rift: New Seismic Constraints from Puysegur Margin, New Zealand

2020 ◽  
Author(s):  
Brandon Shuck ◽  
Harm Van Avendonk ◽  
Sean Gulick ◽  
Michael Gurnis ◽  
Rupert Sutherland ◽  
...  
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
Plate Boundary ◽  
Strike Slip ◽  
Rift Basin ◽  
The South ◽  
Subduction Initiation ◽  
The North ◽  
Collision Zone ◽  
Seismic Images

&lt;p&gt;Critical ingredients and conditions necessary to initiate a new subduction zone are debated. General agreement is that subduction initiation likely takes advantage of previously weakened lithosphere and may prefer to nucleate along pre-existing plate boundaries. To evaluate how past tectonic regimes and lithospheric structures might facilitate underthrusting and lead to self-sustaining subduction, we present an analysis of the Puysegur Margin, a young subduction zone with a rapidly evolving tectonic history.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The Puysegur Margin, south of New Zealand, currently accommodates convergence between the Australian and Pacific plates, exhibits an active seismic Benioff zone, a deep ocean trench, and young adakitic volcanism on the overriding plate. Tectonic plate reconstructions show that the margin experienced a complicated transformation from rifting to seafloor spreading, to strike-slip motion, and most recently to incipient subduction, all in the last ~45 million years. Details of this tectonic record remained incomplete due to the lack of high-quality seismic data throughout much of the margin.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Here we present seismic images from the South Island Subduction Initiation Experiment (SISIE) which surveyed the Puysegur region February-March, 2018. SISIE acquired 1252 km of deep-penetrating multichannel seismic (MCS) data on 7 transects, including 2 regional dip lines coincident with Ocean Bottom Seismometers (OBS) deployments which extend (west to east) from the incoming Australian plate, across the Puysegur Trench and Puysegur Ridge, over the Solander Basin and onto the continental Campbell Plateau margin.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;We integrate pre-stack depth migrated MCS profiles with OBS tomography models to constrain the tectonic development of the Puysegur Margin. Based on our results we propose the following Cenozoic evolution: (1) The entire Solander Basin contains thinned continental crust which formed from orthogonal stretching between the Campbell and Challenger plateaus during the Eocene-Oligocene. This phase of rifting was more pronounced to the south, producing thinner crust with abundant syn-rift volcanism across a wider rift-basin, in contrast to the relatively thicker crust, moderate syn-rift volcanism and narrower rift basin in the north. (2) Strike-slip deformation subsequently developed along Puysegur Ridge, west of the locus of rifting and within relatively unstretched continental lithosphere. This young strike-slip plate boundary translated unstretched crust northward causing an oblique continent-collision zone, which led to a transpressional pattern of distributed left-stepping, right-lateral faults. (3) Subduction initiation was aided by large density contrasts as oceanic lithosphere translated from the south was forcibly underthrust beneath the continent-collision zone. Early development of oblique subduction generated modest and widespread reactivation of faults in the upper plate. (4) Present-day, the Puysegur Trench shows a spatiotemporal transition from nearly mature subduction in the north to a recently initiated stage along the southernmost margin, requiring a southward propagation of subduction through time.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Our new seismic images suggest subduction initiation at the Puysegur Margin was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the developing plate boundary. The Puysegur Margin demonstrates that forced nucleation along a strike-slip boundary is a viable subduction initiation model and should be considered throughout Earth&amp;#8217;s history.&lt;/p&gt;

Heat-Etching with a Bullivant Type II Simple Freeze-Cleave Device

1970 ◽  
Vol 28 ◽  
pp. 106-107 ◽  
Author(s):  
Ronald S. Weinstein ◽  
N. Scott McNutt
Keyword(s):  
New Zealand ◽  
General Hospital ◽  
Massachusetts General Hospital ◽  
Type I ◽  
Type Ii ◽  
Collaborative Effort ◽  
Temperature And Pressure ◽  
The University

The Type I simple cold block device was described by Bullivant and Ames in 1966 and represented the product of the first successful effort to simplify the equipment required to do sophisticated freeze-cleave techniques. Bullivant, Weinstein and Someda described the Type II device which is a modification of the Type I device and was developed as a collaborative effort at the Massachusetts General Hospital and the University of Auckland, New Zealand. The modifications reduced specimen contamination and provided controlled specimen warming for heat-etching of fracture faces. We have now tested the Mass. General Hospital version of the Type II device (called the “Type II-MGH device”) on a wide variety of biological specimens and have established temperature and pressure curves for routine heat-etching with the device.

Literary Histories

2018 ◽  
Author(s):  
Eva-Marie Kröller
Keyword(s):  
New Zealand ◽  
Collective Identity ◽  
Literary History ◽  
English Language ◽  
South Pacific ◽  
The South ◽  
Cultural Elite ◽  
Historical Methodology ◽  
Literary Histories

This chapter discusses national literary histories in Australia, Canada, New Zealand, and the South Pacific and summarises the book's main findings regarding the construction and revision of narratives of national identity since 1950. In colonial and postcolonial cultures, literary history is often based on a paradox that says much about their evolving sense of collective identity, but perhaps even more about the strains within it. The chapter considers the complications typical of postcolonial literary history by focusing on the conflict between collective celebration and its refutation. It examines three issues relating to the histories of English-language fiction in Australia, Canada, New Zealand, and the South Pacific: problems of chronology and beginnings, with a special emphasis on Indigenous peoples; the role of the cultural elite and the history wars in the Australian context; and the influence of postcolonial networks on historical methodology.

Strike-slip ground-surface rupture (Greendale Fault) associated with the 4 September 2010 Darfield earthquake, Canterbury, New Zealand

2011 ◽  
Vol 44 (3) ◽  
pp. 283-291 ◽  
Author(s):  
D.J.A. Barrell ◽  
N.J. Litchfield ◽  
D.B. Townsend ◽  
M. Quigley ◽  
R.J. Van Dissen ◽  
...  
Keyword(s):  
New Zealand ◽  
Ground Surface ◽  
Strike Slip ◽  
Surface Rupture

scholarly journals Exploring the Role of Family and School as Spaces for 1.5 Generation South Korean’s Adjustment and Identity Negotiation in New Zealand: A Qualitative Study

2020 ◽  
Vol 17 (12) ◽  
pp. 4408
Author(s):  
Su Yeon Roh ◽  
Ik Young Chang
Keyword(s):  
New Zealand ◽  
Identity Negotiation ◽  
Identity Status ◽  
Traditional Values ◽  
The South ◽  
1.5 Generation ◽  
South Korean ◽  
The Family ◽  
Home And School ◽  
At Home

To date, the majority of research on migrant identity negotiation and adjustment has primarily focused on adults. However, identity- and adjustment-related issues linked with global migration are not only related to those who have recently arrived, but are also relevant for their subsequent descendants. Consequently, there is increasing recognition by that as a particular group, the “1.5 generation” who were born in their home country but came to new countries in early childhood and were educated there. This research, therefore, investigates 1.5 generation South Koreans’ adjustment and identity status in New Zealand. More specifically, this study explores two vital social spaces—family and school—which play a pivotal role in modulating 1.5 generation’s identity and adjustment in New Zealand. Drawing upon in-depth interviewing with twenty-five 1.5 generation Korean-New Zealanders, this paper reveals that there are two different experiences at home and school; (1) the family is argued to serve as a key space where the South Korean 1.5 generation confirms and retains their ethnic identity through experiences and embodiments of South Korean traditional values, but (2) school is almost the only space where the South Korean 1.5 generation in New Zealand can acquire the cultural tools of mainstream society through interaction with English speaking local peers and adults. Within this space, the South Korean 1.5 generation experiences the transformation of an ethnic sense of identity which is strongly constructed at home via the family. Overall, the paper discusses that 1.5 generation South Koreans experience a complex and contradictory process in negotiating their identity and adjusting into New Zealand through different involvement at home and school.

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