Crustal evolution of the submarine plateaux of New Zealand and their tectonic reconstruction based on crustal balancing

Tectonics, marine geophysics, plate-tectonic reconstruction, new zealand, antarctica, seismic refraction/wide-angle reflection, Gondwana break-up. - The last supercontinent fell into pieces with the break-up of Gondwana. In this context, the separation of the microcontinent of New Zealand from Antarctica is a jigsaw puzzle of many pieces. Its parts lay at the convergent margin of East Gondwana, which changed into a divergent margin within a geologically short time. That is why the microcontinent of New Zealand experienced different tectonic regimes and phases of the Wilson cycle. Although it is a good object of investigation due to its changing history, remarkably little is known about the submerged parts of the microcontinent. Knowledge of the magmatic-tectonic development of the submarine plateaux such as Campbell Plateau and Chatham Rise will improve the understanding of the processes that led to the late Gondwana break-up, and, in turn, lead to better reconstructions of East Gondwana, as Zealandia is a key piece in plate-kinematic reconstructions of this part of Gondwana. The central part of this thesis deals with the separation process of Zealandia from Antarctica leading to an improved reconstruction of New Zealand with emphasis on the submarine plateaux. Bounty Trough separating Chatham Rise from Campbell Plateau, and the Great South Basin separating Campbell Plateau from the South Island are investigated with seismic refraction and reflection methods. They are interpreted jointly with magnetic and gravity data. The results of crustal thickness modelling based on satellite gravity data are combined with existing information about crustal thickness of Zealandia. With these data ...thesi

Crustal evolution of the submarine plateaux of New Zealand and their tectonic reconstruction based on crustal balancing

The last supercontinent fell into pieces with the break-up of Gondwana. In this context, the separation of the microcontinent of New Zealand from Antarctica is a jigsaw puzzle of many pieces. Its parts lay at the convergent margin of East Gondwana, which changed into a divergent margin within a geologically short time. That is why the microcontinent of New Zealand experienced different tectonic regimes and phases of the Wilson cycle. Although it is a good object of investigation due to its changing history, remarkably little is known about the submerged parts of the microcontinent. Knowledge of the magmatic-tectonic development of the submarine plateaux such as Campbell Plateau and Chatham Rise will improve the understanding of the processes that led to the late Gondwana break-up, and, in turn, lead to better reconstructions of East Gondwana, as Zealandia is a key piece in plate-kinematic reconstructions of this part of Gondwana.The central part of this thesis deals with the separation process of Zealandia from Antarctica leading to an improved reconstruction of New Zealand with emphasis on the submarine plateaux. Bounty Trough separating Chatham Rise from Campbell Plateau, and the Great South Basin separating Campbell Plateau from the South Island are investigated with seismic refraction and reflection methods. They are interpreted jointly with magnetic and gravity data. The results of crustal thickness modelling based on satellite gravity data are combined with existing information about crustal thickness of Zealandia. With these data, a crustal thickness grid is calculated which creates the basis for a novel technique for plate-kinematic reconstructions in areas of crustal thinning and in the absence of magnetic seafloor anomalies. This reconstruction consists of crustal balancing to compensate for extension within basins and troughs.The seismic refraction and reflection survey across the Bounty Trough shows a strongly thinned crust in the trough. Zones of high P-and S-wave velocities were found in the lower crust shows. Comparison of the P-wave model and a Poisson's ratio model with rock type diagrams leads to a compositional model of the crust. The joint interpretation of all models suggests that extension in the Bounty Trough proceeded until seafloor spreading in the Middle Bounty Trough began. Geophysical data from the Great South Basin show underplating beneath the Central Campbell Plateau and crustal thinning in the basin, to a lesser extent than in Bounty Trough. Comparison of the seismic data with existing magnetic data across the Great South Basin (Stokes Magnetic Anomaly System - SMAS) and the Campbell Plateau (Campbell Magnetic Anomaly System - CMAS) resulted in the conclusion that these anomaly systems have different origins or histories. Contrary to the results of this thesis, previous investigations assumed a common origin of SMAS and CMAS. Plate-kinematic reconstruction on the base of observations and interpretations combined with existing and modelled crustal thickness shows that extension in Bounty Trough and Great South Basin as well as in New Caledonia Basin was significantly less than previously assumed. The novel technique for plate tectonic reconstructions in thinned continental crust presented in this thesis has the potential to improve plate-kinematic reconstructions for early break-up settings and failed rift systems with stretched continental crust worldwide

Die krustale Entwicklung der submarinen Plateaus Neuseelands und ihre tektonische Rekonstruktion mit Hilfe von Krustenbilanzierungen

The last supercontinent fell into pieces with the break-up of Gondwana. In this context, the separation of the microcontinent of New Zealand from Antarctica is a jigsaw puzzle of many pieces. Its parts lay at the convergent margin of East Gondwana, which changed into a divergent margin within a geologically short time. That is why the microcontinent of New Zealand experienced different tectonic regimes and phases of the Wilson cycle. Although it is a good object of investigation due to its changing history, remarkably little is known about the submerged parts of the microcontinent. Knowledge of the magmatic-tectonic development of the submarine plateaux such as Campbell Plateau and Chatham Rise will improve the understanding of the processes that led to the late Gondwana break-up, and, in turn, lead to better reconstructions of East Gondwana, as Zealandia is a key piece in plate-kinematic reconstructions of this part of Gondwana.The central part of this thesis deals with the separation process of Zealandia from Antarctica leading to an improved reconstruction of New Zealand with emphasis on the submarine plateaux. Bounty Trough separating Chatham Rise from Campbell Plateau, and the Great South Basin separating Campbell Plateau from the South Island are investigated with seismic refraction and reflection methods. They are interpreted jointly with magnetic and gravity data. The results of crustal thickness modelling based on satellite gravity data are combined with existing information about crustal thickness of Zealandia. With these data, a crustal thickness grid is calculated which creates the basis for a novel technique for plate-kinematic reconstructions in areas of crustal thinning and in the absence of magnetic seafloor anomalies. This reconstruction consists of crustal balancing to compensate for extension within basins and troughs.The seismic refraction and reflection survey across the Bounty Trough shows a strongly thinned crust in the trough. Zones of high P-and S-wave velocities were found in the lower crust shows. Comparison of the P-wave model and a Poisson's ratio model with rock type diagrams leads to a compositional model of the crust. The joint interpretation of all models suggests that extension in the Bounty Trough proceeded until seafloor spreading in the Middle Bounty Trough began. Geophysical data from the Great South Basin show underplating beneath the Central Campbell Plateau and crustal thinning in the basin, to a lesser extent than in Bounty Trough. Comparison of the seismic data with existing magnetic data across the Great South Basin (Stokes Magnetic Anomaly System - SMAS) and the Campbell Plateau (Campbell Magnetic Anomaly System - CMAS) resulted in the conclusion that these anomaly systems have different origins or histories. Contrary to the results of this thesis, previous investigations assumed a common origin of SMAS and CMAS. Plate-kinematic reconstruction on the base of observations and interpretations combined with existing and modelled crustal thickness shows that extension in Bounty Trough and Great South Basin as well as in New Caledonia Basin was significantly less than previously assumed. The novel technique for plate tectonic reconstructions in thinned continental crust presented in this thesis has the potential to improve plate-kinematic reconstructions for early break-up settings and failed rift systems with stretched continental crust worldwide

Is the Bounty Trough, off New Zealand, an aborted rift?

Remarkably little is known about the Cretaceous rifting process between New Zealand and Antarctica as well as within the submarine parts of the microcontinent of New Zealand itself. The Bounty Trough offers good insights into these break-up processes. Here we present results from a combined gravity, multichannel seismic and wide-angle reflection/refraction seismic transect across the Bounty Trough and interpret this on the basis of velocity distribution and crustal composition derived from Poisson's ratio and P-wave velocity. The lower crust exhibits a high-velocity (vp "ca." 7 - 7.7 km/s, vs "ca." 3.9 - 4.5 km/s), high-density body ("rho" "equals" 3.02 kg/cm³) at the location of the most thinned crust of the Bounty Trough. In this part, crustal thickness is reduced from 22 - 24 km beneath Chatham Rise and Campbell Plateau to about 9 km. We interpret this high-velocity/density body as a magmatic intrusion into a thinned continental crust. Our results show that the Cretaceous rifting of the Bounty Trough is very likely not the result of back-arc extension caused by the Hikurangi Plateau subduction in the Gondwana margin, but of continental break-up processes related to the separation of New Zealand from Antarctica. Rifting ceased at the onset of seafloor spreading, so that only little oceanic crust was produced in the Middle Bounty Trough. Comparisons with the Oslo Rift and the Ethiopian/Kenya Rift indicate analogue systems and imply a stretching model that combines uniform stretching and simple shear extension

Schallausbreitung entlang stationärer Messstrecken die VOICE Experimente

No Abstract availabl

Analysis of 3-component OBS-data from the Campbell Plateau, New Zealand: A preliminary model

The Campbell-Plateau is a large submarine continental plateau lying to the southeastof New Zealand and separated from the landmass of New Zealand by a series ofdeep extensional sedimentary basins and geomorphologic deeps. The region (withNew Zealand) formed a part of Gondwana until extension and subsequent seafloorspreading formed the Southern Ocean at about 82 Ma. Although the timing of break-upis well defined, the processes of break-up and the development of the continentalfragment forming Campbell Plateau are not yet understood. To investigate theprocesses of evolution of submarine plateaux, a geophysical survey was conductedacross the Campbell Plateau in January and February 2003. The survey carried out aseismic (OBS) transect with a high density of OBSs (spacing ~ 10 - 20km) incombination with a series of crustal seismic reflection lines. It crossed the GreatSouth Basin and poorly known east-west trending inferred extensional basins on theCampbell Plateau and in the Bounty Trough. The large number of multicomponentOBS recordings enabled us to set up a densely spaced model based oncompressional as well as shear waves, which provides the possibility to revealinformation about lithologic properties as Poisson ratios. A preliminary model ofCampbell Plateau and Bounty Trough, based on travel-time inversion will bepresented here

Plattenkinematische Rekonstruktionen mittels Bilanzierung von Krustenmächtigkeiten

Plattenkinematische Rekonstruktionen mit herkömmlichen Methoden können zu großen Fehlern führen, wenn sie in Regionen angewandt werden, in denen Spreizungsanomalien und Fracture Zones fehlen. Die Folgen solcher Fehler sind Überlappungen von Platten, weil deren Ausdehnung in früheren Zeiten geringer ist als die Annahme starrer Plattengrenzen vorhersagt. Dies ist insbesondere der Fall in gedehnter kontinentaler Kruste, weil hier die Information, die in ozeanischer Kruste gespeichert sind, fehlen. Dort ist die Krustenmächtigkeit oft das einzige Indiz zur Rekonstruktion. Liegen flächenhafte Krustenmächtigkeitsdaten vor, so können damit die Lage der Platten rekonstruiert werden.Wir stellen eine neue Rekonstruktionsmethode vor, die eine Krustenmächtigkeitskarte aufteilt in verschiedene Platten, indem Extension durch tiefe Störungen simuliert wird. Dadurch können Teile des Krustenmächtigkeitsgrids wie in einer herkömmlichen Rekonstruktionsmethode rotiert und gegeneinander verschoben werden. Wird eine Verteilung der Krustenmächtigkeiten vor der Extension angenommen werden (z.B. gleichmäßige Mächtigkeiten), kann dies die Qualität einer Rotation anzeigen und verschiedene Rotationen können miteinander verglichen werden, so daß der beste Rotationspol ermittelt werden kann. Wir zeigen den Erfolg dieser Methode am Beispiel Neuseelands, das von etlichen Gebieten gedehnter kontinentaler Kruste, wie z.B. dem Great South Basin, umgeben ist