Tectonic drivers and the influence of the Kerguelen plume on seafloor spreading during formation of the early Indian Ocean |
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| Institution: | 1. Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia;2. ARC Centre of Excellence in Ore Deposits (CODES), School of Physical Sciences, University of Tasmania, Private Bag 79, Tasmania 7001, Australia;3. Earthbyte Group, School of Geosciences, University of Sydney, Sydney, New South Wales, 2006, Australia;4. Division of Earth Sciences, School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2351, Australia;5. Department of Earth and Planetary Sciences, Macquarie University 2109, New South Wales, Australia;1. Résidence Croix du Sud, Rue Henri de Montherlant, F-33400 Talence, France;2. Lebanese University, Faculty of Sciences II, Department of Natural Sciences, Fanar, Fanar-Matn, P.O. Box 26110217, Lebanon;3. Muséum National d''Histoire Naturelle, Institut de Systématique, Evolution, Biodiversité, ISYEB, UMR 7205 CNRS UPMC EPHE, CP50, 45 rue Buffon, F-75005 Paris, France;1. Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK;2. Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK;3. Dipartimanto di Scienze della Terra, Universita'' degli Studi di Firenze, Via La Pira 4, 50121 Firenze, Italy;4. Faculteit der Aardwetenschappen, Vrije Universiteit, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands;5. GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg, Schloβgarten 5, D-91054 Erlangen, Germany;1. Department of Earth and Planetary Sciences, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Macquarie University, Sydney, NSW 2109, Australia;2. Resources Division, Geoscience Australia, Canberra, ACT 2601, Australia;1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1–3, 24148 Kiel, Germany;2. Kiel University, Institute of Geosciences, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany;1. Utrecht University, Faculty of Earth Sciences, Utrecht, The Netherlands;2. Sorbonne Universités, UPMC Univ Paris 06, CNRS, Institut des Sciences de la Terre de Paris (iSTeP), 4 place Jussieu, 75005 Paris, France;3. Department of Geosciences, University of Tübingen, Tübingen, Germany;4. ETH-Zurich, Institute of Geophysics, Sonnegstrasse 5, Zurich, Switzerland |
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| Abstract: | The Perth Abyssal Plain (PAP), located offshore southwest Australia, formed at the centre of Mesozoic East Gondwana breakup and Kerguelen plume activity. Despite its importance as a direct and relatively undisturbed recorder of this early spreading history, sparse geophysical data sets and lack of geological sampling hamper our understanding of the evolution of the PAP. This study combines new bathymetric profiles across the PAP with petrographic and geochemical data from the first samples ever to be dredged from the flanks of the Dirck Hartog Ridge (DHR), a prominent linear bathymetric feature in the central PAP, to better constrain the formation of the early Indian Ocean floor and the influence of the Kerguelen plume. Seafloor spreading in the PAP initiated at ~ 136 Ma with spreading observed to occur at (half) rates of ~ 35 mm/yr. Changes in spreading rate are difficult to discern after the onset of the Cretaceous Quiet Zone at ~ 120 Ma, but an increase in seafloor roughness towards the centre of the PAP likely resulted from a half-spreading rate decrease from 35 mm/yr (based on magnetic reversals) to ~ 24 mm/yr at ~ 114 Ma. Exhumed gabbro dredged from the southernmost dredge site of the DHR supports a further slowdown of spreading immediately prior to full cessation at ~ 102 Ma. The DHR exhibits a high relief ridge axis and distinctive asymmetry that is unusual compared to most active or extinct spreading centres. The composition of mafic volcanic samples varies along the DHR, from sub-alkaline dolerites with incompatible element concentrations most similar to depleted-to-normal mid-ocean ridge basalts in the south, to alkali basalts similar to ocean island basalts in the north. Therefore, magma sources and degrees of partial melting varied in space and time. It is likely that the alkali basalts are a manifestation of later excess volcanism, subsequent to or during the cessation of spreading. In this case, enriched signatures may be attributed tectonic drivers and melting of a heterogeneous mantle, or to an episodic influence of the Kerguelen plume over distances greater than 1000 km. We also investigate possible scenarios to explain how lower crustal rocks were emplaced at the crest of the southern DHR. Our results demonstrate the significance of regional tectonic plate motions on the formation and deformation of young ocean crust, and provide insight into the unique DHR morphology. |
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