University Of Tasmania

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Tectonic history of the South-West Pacific region

posted on 2023-05-26, 20:47 authored by Griffiths, JR
This study attempts to deduce the Phanerozoic tectonic relation-ships of Australia, Antarctica and New Zealand, and then to discuss in greater detail the evolution of New Zealand and of the continental margin of south-cast Australia. Plate tectonics provides a broad conceptual framework for the syntheses proposed, but the emphasis throughout is based on objective analysis of the data available. Flow-charts and time-space plots are developed as aids in construction and evaluation of the tectonic syntheses. Various criteria are used to define and reassemble Australia, Antarctica, New Zealand and surrounding areas of continental crust as parts of the former Gondwanaland in the Mesozoic. A brief review of the Paleozoic (exposed mainly in eastern Australia), outlines the pro-gressive development and cratonisation of a very complex orogenic belt bordering the Pacific Ocean. During the Mesozoic an \Atlantic-type\" continental margin was established east of this belt and is now best exposed in New Zealand. Orogenesis along this margin accompanied sub-duction of the Pacific plate during the Upper Jurassic to Lower Cret-aceous Rangitata Orogeny. The resulting orthotectonic belt exhibits contrasting structural and metamorphic styles of foreland and oceanward sides. Fragmentation of Gondwanaland began in the Jurassic by develop-ment of an extensive rift valley system which is studied in detail in the sedimentary basins of south-east Australia (Otway Bass and Gippsland Basins) largely from sub-surface oil-company exploration data. The structural evolution of these basins is controlled by the initial rift configuration and neither pre-existing basement structures nor transform faults related to Tertiary sea-floor spreading appear to have much influence. Published marine magnetic data constrain a geometric synthesis of the sea-floor spreading history. From 85 to 60 million years ago the Tasman Sea was opening between Australia Antarctica and New Zea-land about a rotation centre near northern Queensland. Following separation of Australia and Antarctica about 55 million years ago a new three-plate geometry was established. In this system the Australian-Pacific plate boundary displays a complex history involving regions of subduction and transcurrent faulting. The Alpine Fault (which became active about 20 million years ago) and the severe Tertiary deformation in New Zealand are closely related to the sea-floor spreading history. The various aspects of the regional tectonic history studied all indicate that the plate tectonic hypothesis is both a valid and useful new approach in geology. They are also predictive and point to many new problems which might be investigated."


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Copyright 1973 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (PhD) - University of Tasmania, 1974. Bibliography: p. R1-R28

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