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GEOREF RECORD

A wide ocean-continent transition along the southwestern Australian margin; first results of the MARGAU/MD110 cruise

Marie-Odile Beslier, Jean-Yves Royer, Jacques Girardeau, Peter J. Hill, Eric Boeuf, Cameron Buchanan, Fabienne Chatin, Gilles Jacovetti, Alain Moreau, Marc Munschy, Celine Partouche, Ursula Robert and Steve Thomas
Une large transition continent-ocean en pied de marge sud-ouest australienne; premiers resultats de la campagne MARGAU/MD110
Bulletin de la Societe Geologique de France (2004) 175 (6): 629-641

Abstract

Introduction and geodynamic setting. - Syn-rift exhumation of mantle rocks in a continental breakup zone was highlighted along the present-day west Iberian passive margin [e.g. Boillot et al., 1988, 1995; Whitmarsh et al., 1995, 2001; Beslier et al., 1996; Brun and Beslier, 1996; Boillot and Coulon, 1998; Krawczyk et al., 1996; Girardeau et al., 1998] and along the fossil Tethyan margins [e.g. Froitzheim and Manatschal, 1996; Manatschal and Bernoulli, 1996; Marroni et al., 1998; Muntener et al., 2000; Desmurs et al., 2001]. Along the west Iberian margin, serpentinized peridotite and scarce gabbro and basalt lay directly under the sediments, over a 30 to 130 km-wide transition between the thinned continental crust and the first oceanic crust [Girardeau et al., 1988, 1998; Kornprobst and Tabit, 1988; Boillot et al., 1989; Beslier et al., 1990, 1996; Cornen et al., 1999]. The formation of a wide ocean-continent transition (OCT), mostly controlled by tectonics and associated with an exhumation of deep lithospheric levels, would be an essential stage of continental breakup and a characteristic of magma-poor passive margins. The southwest Australian margin provides an opportunity to test and to generalize the models proposed for the west Iberian margin, as both margins present many analogies. The south Australian margin formed during the Gondwana breakup in the Mesozoic, along a NW-SE oblique extension direction [Willcox and Stagg, 1990]. From north to south, the continental slope is bounded by (1) a magnetic quiet zone (MQZ) where the nature of the basement is ambiguous [Talwani et al., 1979; Tikku and Cande, 1999; Sayers et al., 2001], (2) a zone where the basement shows a rough topography associated with poorly expressed magnetic anomalies [Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999; Sayers et al., 2001], and which is the eastward prolongation of the Diamantina Zone, and (3) an Eocene oceanic domain. The continental breakup zone is believed to be located near or at the southern edge of the MQZ [Cande and Mutter, 1982; Veevers et al., 1990; Sayers et al., 2001]. Breakup is dated at 125 Ma [Stagg and Willcox, 1992], 95+ or -5 Ma [Veevers, 1986] or at 83 Ma [Sayers et al., 2001], and followed by ultra-slow seafloor spreading until the Eocene (43 Ma), and fast spreading afterwards [Weissel and Hayes, 1972; Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999]. The western end of the margin (fig. 1) is starved and bounded in the OCT by basement ridges where peridotite, gabbro and basalt were previously dredged [Nicholls et al., 1981]. Altimetry data [Sandwell and Smith, 1997] show that some of these ridges are continuous over 1500 km along the OCT of the south Australian margin and of the conjugate Antarctic margin. The objectives of the MARGAU/MD110 cruise (May-June 1998; [Royer et al., 1998]; fig. 2) were to define the morpho-structure and the nature and evolution of the basement in the SW Australian OCT. An area of 180 000 km (super 2) was explored with swath bathymetry. Gravimetric data (11382 km) were simultaneously recorded whereas few single channel seismic (1353 km) and magnetic (5387 km) data were obtained due to technical difficulties. Crystalline basement rocks, made of varied and locally well-preserved lithologies, were dredged at 11 sites located on structural highs


ISSN: 0037-9409
EISSN: 1777-5817
Coden: #02538
Serial Title: Bulletin de la Societe Geologique de France
Serial Volume: 175
Serial Issue: 6
Title: Une large transition continent-ocean en pied de marge sud-ouest australienne; premiers resultats de la campagne MARGAU/MD110
Translated Title: A wide ocean-continent transition along the southwestern Australian margin; first results of the MARGAU/MD110 cruise
Affiliation: CNRS, Geosciences Azur, Villefranche-sur-Mer, France
Pages: 629-641
Published: 2004
Text Language: French
Summary Language: English
Publisher: Societe Geologique de France, Paris, France
References: 46
Accession Number: 2005-038707
Categories: Solid-earth geophysicsApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., sketch maps
S38°30'00" - S35°00'00", E108°00'00" - E120°00'00"
Secondary Affiliation: Universite de Nantes, FRA, FranceGeoscience Australia, AUS, AustraliaEOST, FRA, FranceUniversite Pierre et Marie Curie, FRA, France
Country of Publication: France
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200514
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