scholarly journals Geophysical Studies in the Southwest Pacific : Primarily Studies of Crustal Structure between New Zealand and Antarctica

2021 ◽  
Author(s):  
◽  
Robin Keith Halcro Falconer
Keyword(s):  
New Zealand ◽  
Plate Tectonics ◽  
Magnetic Anomalies ◽  
Pacific Basin ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Southwest Pacific ◽  
Plate Movement ◽  
Model Studies ◽  
The Pacific

<p>Geophysical data - primarily magnetic field measurements, bathymetry, and seismicity data - are presented for the area between New Zealand and Antarctica from approximately 145[degrees]W to 155[degrees]E. The data are used to determine the structure of the Pacific-Antarctic boundary, the oceanic part of the Pacific plate and the area of intersection of the Indian, Pacific and Antarctic plates. In the southwest Pacific basin the magnetic anomalies are very clear and an extensive pattern of anomaly lineations with some offsets is mapped. The magnetic anomalies show that the uniform Pacific basin area formed between about 83 and 63 mybp. The Pacific-Antarctic boundary is shown to differ either side of about 175[degrees]W. To the east it is a relatively uniform aseismic spreading ridge, offset by some transform faults. West of 175[degrees]W, to 161[degrees]E, the boundary consists of a seismically active zone of disturbed bathymetry and magnetic anomalies striking about N.70[degrees]W. The zone, the Pacific-Antarctic fracture zone, probably consists of several fractures striking about N45[degrees]W. The area between the Pacific-Antarctic boundary and the southwest Pacific basin represents the interval 10 to -55 mybp, and only in the east are anomaly lineations clear. The Indian-Antarctic Pacific triple junction is near 61.5[degrees]S, 161[degrees]E and is a stable ridge-fault-fault junction; the Indian-Antarctic boundary being the ridge. Plate tectonics is applied to the area and the structure is shown to fit, and be explained by a different rotation pole for each of the major intervals indicated by the structure, i.e. 0-10 mybp, 10-63 mybp and 63-80 mybp. The poles, with rotation rates deduced from the magnetic anomalies, are used to reconstruct the position of New Zealand relative to Antarctica at 80 mybp. The two continents probably started to separate at close to 83 mybp. The times of the major changes of structure and plate movement in the area are shown to coincide with major plate movement changes in the southwest Pacific area and in the rest of the world. A new method for determining poles of rotation, based only on epicentre locations is presented, The method is applied to independently determine the Indian-Pacific, Pacific-Antarctic and Indian-Antarctic poles. The poles should form a consistent. set and they do. The method yields effectively instantaneous poles, is quantitative, and is applicable to most plate boundaries. Earthquake magnitude-frequency relationship b values for the plate boundaries in the area are determined. Comparisons with results from elsewhere indicate an association of high b with high temperature and conversely. Several factors which have previously been suggested as determining b value are shown to not be determinants. A revised and extended magnetic reversal time scale based on model studies of the southwest Pacific basin anomalies is presented. Other model studies indicate that a magnetized layer thickness of at least 2 km is probable. Variations of anomaly amplitudes are studied. A detailed study of the application of numerical correlation techniques to magnetic anomalies is presented. It is concluded that horizontal scale variations and discontinuities in profiles can be critical. Methods for over-coming some of the problems, and for determining quantitative error estimates, are. given. The methods, and conclusions, are applicable to any correlation problem.</p>

scholarly journals Geophysical Studies in the Southwest Pacific : Primarily Studies of Crustal Structure between New Zealand and Antarctica

2021 ◽  
Author(s):  
◽  
Robin Keith Halcro Falconer
Keyword(s):  
New Zealand ◽  
Plate Tectonics ◽  
Magnetic Anomalies ◽  
Pacific Basin ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Southwest Pacific ◽  
Plate Movement ◽  
Model Studies ◽  
The Pacific

<p>Geophysical data - primarily magnetic field measurements, bathymetry, and seismicity data - are presented for the area between New Zealand and Antarctica from approximately 145[degrees]W to 155[degrees]E. The data are used to determine the structure of the Pacific-Antarctic boundary, the oceanic part of the Pacific plate and the area of intersection of the Indian, Pacific and Antarctic plates. In the southwest Pacific basin the magnetic anomalies are very clear and an extensive pattern of anomaly lineations with some offsets is mapped. The magnetic anomalies show that the uniform Pacific basin area formed between about 83 and 63 mybp. The Pacific-Antarctic boundary is shown to differ either side of about 175[degrees]W. To the east it is a relatively uniform aseismic spreading ridge, offset by some transform faults. West of 175[degrees]W, to 161[degrees]E, the boundary consists of a seismically active zone of disturbed bathymetry and magnetic anomalies striking about N.70[degrees]W. The zone, the Pacific-Antarctic fracture zone, probably consists of several fractures striking about N45[degrees]W. The area between the Pacific-Antarctic boundary and the southwest Pacific basin represents the interval 10 to -55 mybp, and only in the east are anomaly lineations clear. The Indian-Antarctic Pacific triple junction is near 61.5[degrees]S, 161[degrees]E and is a stable ridge-fault-fault junction; the Indian-Antarctic boundary being the ridge. Plate tectonics is applied to the area and the structure is shown to fit, and be explained by a different rotation pole for each of the major intervals indicated by the structure, i.e. 0-10 mybp, 10-63 mybp and 63-80 mybp. The poles, with rotation rates deduced from the magnetic anomalies, are used to reconstruct the position of New Zealand relative to Antarctica at 80 mybp. The two continents probably started to separate at close to 83 mybp. The times of the major changes of structure and plate movement in the area are shown to coincide with major plate movement changes in the southwest Pacific area and in the rest of the world. A new method for determining poles of rotation, based only on epicentre locations is presented, The method is applied to independently determine the Indian-Pacific, Pacific-Antarctic and Indian-Antarctic poles. The poles should form a consistent. set and they do. The method yields effectively instantaneous poles, is quantitative, and is applicable to most plate boundaries. Earthquake magnitude-frequency relationship b values for the plate boundaries in the area are determined. Comparisons with results from elsewhere indicate an association of high b with high temperature and conversely. Several factors which have previously been suggested as determining b value are shown to not be determinants. A revised and extended magnetic reversal time scale based on model studies of the southwest Pacific basin anomalies is presented. Other model studies indicate that a magnetized layer thickness of at least 2 km is probable. Variations of anomaly amplitudes are studied. A detailed study of the application of numerical correlation techniques to magnetic anomalies is presented. It is concluded that horizontal scale variations and discontinuities in profiles can be critical. Methods for over-coming some of the problems, and for determining quantitative error estimates, are. given. The methods, and conclusions, are applicable to any correlation problem.</p>

scholarly journals GEODYNAMICS AND MAGMATISM OF THE PACIFIC-TYPE TRANSFORM MARGINS. ASPECTS AND DISCRIMINANT DIAGRAMS

2021 ◽  
pp. 3-24
Author(s):  
A.V. Grebennikov ◽  
◽  
A.I. Khanchuk ◽  
Keyword(s):  
Continental Margin ◽  
Tectonic Setting ◽  
Island Arc ◽  
Igneous Rocks ◽  
High Alumina ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Convergent Margins ◽  
Oceanic Plate ◽  
Plate Movement

Transform margins represent lithospheric plate boundaries with horizontal sliding of oceanic plate, which in time and space replaced the subduction related convergent margins. This happened due to: spreading ridge–trench intersection (California; Queen Charlotte–Northern Cordilleran, West of the Antarctic Peninsula, and probably the Late Miocene–Pleistocene Southernmost South America) or ridge death along continental margin (Baja California); change in the direction of oceanic plate movement (Western Aleutian–Komandorsk; Southernmost tip of the Andes); and island arc-continent collision (New Guinea Island). Post-subduction magmatism is related to a slab window that resulted either from the spreading ridge collision (subduction) with a continental margin or slab tear formation, or slab break-off after subduction cessation due to other reasons. Igneous magmatic series formed in consequence of these events show diversity of tholeiitic (sub-alkaline), alkaline or calc-alkaline, high-alumina and adakitic rocks. The comprehensive geochemical dataset (more than 2400 analyses) on igneous rocks of the model transform and convergent geodynamic settings allowed to substantiate the most informative triple diagrams for the petrogenic oxides TiO2 × 10 – Fe2O3Tot – MgO and trace elements Nb – La– Yb. Mostly approved for the rock compositions with SiO2 < 63 wt. %, the new plots are capable of distinguishing igneous rocks formed above zones of subduction at an island arc and continental margin (related to convergent margins), from those formed in the tectonic setting of transform margins along continents or island arcs.

Southeast Asian Defense Treaty

1954 ◽  
Vol 8 (4) ◽  
pp. 611-613
Keyword(s):  
United States ◽  
United Kingdom ◽  
New Zealand ◽  
Southeast Asia ◽  
The United States ◽  
The Philippines ◽  
Southeast Asian ◽  
Southwest Pacific ◽  
The Pacific ◽  
Collective Defense

On September 8, 1954, representatives of the United States, United Kingdom, France, the Philippines, Thailand, Pakistan, Australia and New Zealand signed the Southeast Asia Collective Defense Treaty, a protocol designating the areas to which the treaty was to apply, and the Pacific Charter, a declaration setting forth the aims of the eight countries in southeast Asia and the southwest Pacific. Negotiations leading up to the actual signature of the treaty had been underway throughout the summer of 1954 and had culminated in an eight-power conference in Manila which opened on September 6.

High-resolution constraints on LAB structure at the Blanco transform

2020 ◽  
Author(s):  
William Hawley ◽  
James Gaherty
Keyword(s):  
High Resolution ◽  
Azimuthal Anisotropy ◽  
Plate Motion ◽  
Pacific Basin ◽  
Mantle Flow ◽  
Detailed Knowledge ◽  
Plate Boundaries ◽  
Seismic Structure ◽  
The Pacific ◽  
Juan De Fuca

&lt;p&gt;Detailed knowledge of the seismic structure, fabric, and dynamics that surround the oceanic LAB continue to be refined through offshore seismic studies. Previous high-resolution studies in the Pacific basin far from plate boundaries show asthenospheric fabric that aligns neither with the lithospheric fabric (the paleo-spreading direction) nor with absolute plate motion, but rather in between. Here we present preliminary results from the Blanco Transform and Cascadia Initiative experiments, investigating the structure of the Juan de Fuca and Pacific plates on either side of the Blanco Transform. We measure ambient-noise and teleseismic Rayleigh-wave phase velocities, and solve for the period-dependent azimuthal anisotropy on either side of the transform. We will contextualize and interpret the fabrics based on mantle flow inferred from these previous Pacific basin studies.&amp;#160;&lt;/p&gt;

Evolutionary biogeography and tectonic history of the ghost moth families Hepialidae, Mnesarchaeidae, and Palaeosetidae in the Southwest Pacific (Lepidoptera: Exoporia)

Zootaxa ◽  
2018 ◽  
Vol 4415 (2) ◽  
pp. 243 ◽  
Author(s):  
JOHN R. GREHAN ◽  
CARLOS G.C. MIELKE
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
New Caledonia ◽  
Lateral Displacement ◽  
Southwest Pacific ◽  
Biogeographic History ◽  
The Pacific ◽  
Extant Species ◽  
Distribution Ranges ◽  
History Of

The biogeographic history of Exoporia (Lepidoptera) in the Southwest Pacific is reconstructed for genera and species that show distributional boundaries corresponding to tectonic structures in the region. Correlations with tectonic formations of Mesozoic origin such as the Whitsunday Volcanic Province and Otway-Bass-Gippsland Basin system in Australia, the Vitiaz Fracture Zone in northern Melanesia, and the Western Province-Eastern Province boundary, Waitaki Fault Zone, and Waihemo Fault Zone of New Zealand are presented as evidence of an East Gondwana origin for genera and species before the geological separation of Australia and New Zealand. The correlated boundaries also suggest that many extant species retain at least parts of their original East Gondwana distribution ranges. The presence of Exoporia on the northern Melanesian Arc, New Caledonia, and New Zealand is attributed to the tectonic isolation of these areas when East Gondwana expanded into the Pacific following retreat of the Pacific Plate subduction zone. Local endemism of Mnesarchaeidae in New Zealand is interpreted as the result of an original vicariance from a widespread ancestor (‘Exoporia’) resulting in two allopatric descendants —a narrowly distributed Mnesarchoidea and a widely distributed Hepialoidea. The current overlap of these two groups in New Zealand is explained as the result of subsequent range expansion by the Hepialoidea prior to geological fragmentation of East Gondwana. The potential impact of Cretaceous geography on modern distributions is also considered for Exoporia in southern Africa and northern America. Along with lateral displacement of Exoporia, tectonic processes also contributed to the origin of high elevation endemics through a process of passive tectonic uplift. 

scholarly journals A Magnetic Survey of the Southwest Pacific Ocean

2021 ◽  
Author(s):  
◽  
David Irwin Ross
Keyword(s):  
New Zealand ◽  
Pacific Ocean ◽  
Ross Sea ◽  
Magnetic Survey ◽  
Southwest Pacific ◽  
The North ◽  
Magnetic Pattern ◽  
The Pacific ◽  
Profiling Techniques ◽  
Ocean Ridge

<p>The design and construction of a free precession proton magnetometer which give a reading of the field directly in gamma is described. This instrument has been used to obtain magnetic profiles across the Southwest Pacific Ocean during the 1963-65 summer Antarctic supply cruises of H.M.N.Z.S. Endeavour. The magnetic and bathymetric profiler obtained on these cruises have been analysed to determine the nature and structure of the oceanic crust in this region. The region is divided into four divisions. (l) The New Zealand Plateau, with an almost continental crustal thickness. (2) The Southwest Pacific Basin, at a depth of 3,000 fathoms. (3) The Pacific-Antarctic Ridge, pert of the world encircling mind-ocean ridge system. (4) The Ross Sea, an epicontinental sea across the Antarctic continental shelf. Subtraction of the regional field form the magnetic results has enabled a regional field map of the area to be drawn. Comparison with earlier results indicates a westward drift of the earth's field of approximately 0.25 degrees /yr. Some discussion of regional anomalies (~ 100 miles period) has been given. Because of the excellent correlation of magnetic anomalies from track to track across the basin it has been possible to draw an anomaly contour map of this part. This map illustrates the predominantly east-west trend of features over the basin. To the north the features parallel the edge of the New Zealand Plateau. To the south the features swing more towards the Pacific-Antarctic Ridge. A major discontinuity is indicated along a direction 9 degrees E of S meeting the Plateau just southwest of Antipodes Islands. If this discontinuity is extrapolated south to the ridge it meets it at approximately 180 degrees E, where the ridge turns N-E towards Easter Island. Across the ridge the magnetic pattern shows three distinct regions. Over the northern flanks large anomalies are evident but the correlation of anomalies from track to track is very poor. Further south, across the upper flanks, the magnetic records are very much subdued. The extent of this region varies appreciably from track to track. Over the axis of the ridge large, steep-sided anomalies are obtained. These correlate well over part of the region studied. The southern flanks of the ridge are hidden by the Balleny Plateau which seems to form a link between Antarctica and the ridge in this region. The bathymetry records obtained indicate a step-type formation over the ridge. A narrow median valley appears to exist along the axis of the ridge. Some preliminary experimentation has been carried out with continual seismic profiling techniques over the region. The equipment that has been developed and the preliminary results obtained with it are discussed.</p>

scholarly journals A Magnetic Survey of the Southwest Pacific Ocean

2021 ◽  
Author(s):  
◽  
David Irwin Ross
Keyword(s):  
New Zealand ◽  
Pacific Ocean ◽  
Ross Sea ◽  
Magnetic Survey ◽  
Southwest Pacific ◽  
The North ◽  
Magnetic Pattern ◽  
The Pacific ◽  
Profiling Techniques ◽  
Ocean Ridge

<p>The design and construction of a free precession proton magnetometer which give a reading of the field directly in gamma is described. This instrument has been used to obtain magnetic profiles across the Southwest Pacific Ocean during the 1963-65 summer Antarctic supply cruises of H.M.N.Z.S. Endeavour. The magnetic and bathymetric profiler obtained on these cruises have been analysed to determine the nature and structure of the oceanic crust in this region. The region is divided into four divisions. (l) The New Zealand Plateau, with an almost continental crustal thickness. (2) The Southwest Pacific Basin, at a depth of 3,000 fathoms. (3) The Pacific-Antarctic Ridge, pert of the world encircling mind-ocean ridge system. (4) The Ross Sea, an epicontinental sea across the Antarctic continental shelf. Subtraction of the regional field form the magnetic results has enabled a regional field map of the area to be drawn. Comparison with earlier results indicates a westward drift of the earth's field of approximately 0.25 degrees /yr. Some discussion of regional anomalies (~ 100 miles period) has been given. Because of the excellent correlation of magnetic anomalies from track to track across the basin it has been possible to draw an anomaly contour map of this part. This map illustrates the predominantly east-west trend of features over the basin. To the north the features parallel the edge of the New Zealand Plateau. To the south the features swing more towards the Pacific-Antarctic Ridge. A major discontinuity is indicated along a direction 9 degrees E of S meeting the Plateau just southwest of Antipodes Islands. If this discontinuity is extrapolated south to the ridge it meets it at approximately 180 degrees E, where the ridge turns N-E towards Easter Island. Across the ridge the magnetic pattern shows three distinct regions. Over the northern flanks large anomalies are evident but the correlation of anomalies from track to track is very poor. Further south, across the upper flanks, the magnetic records are very much subdued. The extent of this region varies appreciably from track to track. Over the axis of the ridge large, steep-sided anomalies are obtained. These correlate well over part of the region studied. The southern flanks of the ridge are hidden by the Balleny Plateau which seems to form a link between Antarctica and the ridge in this region. The bathymetry records obtained indicate a step-type formation over the ridge. A narrow median valley appears to exist along the axis of the ridge. Some preliminary experimentation has been carried out with continual seismic profiling techniques over the region. The equipment that has been developed and the preliminary results obtained with it are discussed.</p>

scholarly journals Earth evolution and dynamics—a tribute to Kevin Burke

2016 ◽  
Vol 53 (11) ◽  
pp. 1073-1087 ◽  
Author(s):  
Trond H. Torsvik ◽  
Bernhard Steinberger ◽  
Lewis D. Ashwal ◽  
Pavel V. Doubrovine ◽  
Reidar G. Trønnes
Keyword(s):  
Plate Tectonics ◽  
Large Scale ◽  
Plate Boundaries ◽  
Mantle Plumes ◽  
The Past ◽  
The Pacific ◽  
Igneous Provinces ◽  
After Effect ◽  
Essential Contribution ◽  
Lowermost Mantle

Kevin Burke’s original and thought-provoking contributions have been published steadily for the past 60 years, and more than a decade ago he set out to resolve how plate tectonics and mantle plumes interact by proposing a simple conceptual model, which we will refer to as the Burkian Earth. On the Burkian Earth, mantle plumes take us from the deepest mantle to sub-lithospheric depths, where partial melting occurs, and to the surface, where hotspot lavas erupt today, and where large igneous provinces and kimberlites have erupted episodically in the past. The arrival of a plume head contributes to continental break-up and punctuates plate tectonics by creating and modifying plate boundaries. Conversely, plate tectonics makes an essential contribution to the mantle through subduction. Slabs restore mass to the lowermost mantle and are the triggering mechanism for plumes that rise from the margins of the two large-scale low shear-wave velocity structures in the lowermost mantle, which Burke christened TUZO and JASON. Situated just above the core–mantle boundary, beneath Africa and the Pacific, these are stable and antipodal thermochemical piles, which Burke reasons represent the immediate after-effect of the moon-forming event and the final magma ocean crystallization.

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