Dominant symmetry of a conjugate southern Australian and East Antarctic magma-poor rifted margin segment

Abstract

Synthesis and modeling of published deep seismic and potential field data from the conjugate, magma‐poor, rifted margins of the Great Australian Bight, southern Australia, and central Wilkes Land, East Antarctica, show that there is pronounced symmetry of structures in a 300 km wide zone straddling the axis of final breakup. This symmetry is observed consistently for a distance of some hundreds of kilometers along strike. From inboard to outboard, both margins comprise a narrow zone of attenuation of the crystalline continental crust; an approximately 4 km high basement ridge, interpreted as unroofed peridotites, at the location of maximum thinning of the continental crust; and a 60–70 km wide continent‐ocean transition zone that contains a sedimentary basin that may be underlain by altered mantle and fragments of crystalline continental crust. The marked breakup symmetry described here is in contrast to the asymmetry of the Iberia‐Newfoundland margin and is consistent with the operation of a symmetrical extensional detachment system deforming the whole crust in the center of the rift, as envisaged by some numerical models for the continental rifting process.

Tectonomagmatic evolution of the final stages of rifting along the deep conjugate Australian-Antarctic magma-poor rifted margins: Constraints from seismic observations

“…The nature and age of the basement in the ocean‐continent transition (OCT) thus remains currently ill defined. Previous studies agree that this basement is either made of extended continental crust associated with magmatic additions and/or serpentinized mantle peridotites [ Sayers et al , ; Colwell et al , ; Direen et al , ; Ball et al , ]. Particularly, the difficult identification of magnetic anomalies in these ill‐defined domains, not corresponding to clearly defined steady state oceanic crust, questioned the classical way of dating the first magmatic oceanic crust in using the oldest magnetic anomaly [ Sayers et al , ; Colwell et al , ].…”

“…The data discussed here include the AGSO surveys GA199, GA228, and GA229, whose acquisition parameters are described in Table . These seismic data have been already previously published and interpreted in several studies [ Sayers et al , ; Colwell et al , ; Close et al , , ; Direen et al , , , ; Espurt et al , , ; Ball et al , ]. The aim of this paper is thus to propose new interpretations based on a new approach and method.…”

Conjugate rifted margins width and asymmetry: The interplay between lithospheric strength and thermomechanical processes

“…Of particular relevance to our effort are reflection and refraction seismic profiles in the North and South Atlantic [ Gladczenko et al , ; Dean et al , ; Zelt et al , ; Contrucci et al , ; Moulin et al , ; Van Avendonk et al , , ; Hopper et al , ; Osmundsen and Ebbing , ; Klingelhoefer et al , ; Blaich et al , , ; Zálan et al , ; Direen et al , ; Sutra et al , ]. These profiles, summarized in Figure , show a large variability in conjugate margin asymmetry, crustal thickness, nature of the ocean‐continent transition, and margin width landward of demonstrable oceanic crust.…”

Early opening of Australia and Antarctica: New inferences and regional consequences

“…Using this interpretation, he dates the breakup at 95+-5 Ma. Veevers's (1986) COB for the South Australian margin and its Antarctic conjugate delineated from seismic data by Colwell et al (2006) has been used in many subsequent works (Direen et al, 2011;Espurt et al, 2009;Gohl, 2007;O'Brien and Stagg, 2007;Powell et al, 1988;Stagg and Reading, 2007;Veevers and Li, 1991;Williams et al, 2011). A revised interpretation of the COB was proposed by Ball et al (2013) who moves it~100 km-further oceanward.…”