Architecture of the Queensland Trough: implications for the structure and tectonics of the Northeastern Australia Margin

The Queensland Trough is a 155Â°-trending bathymetric deep, located just seaward of the Great Barrier Reef of northeast Australia. The trough reaches a maximum depth of 2800 m, separating the continental shelf and the submerged Queensland Plateau. It is underlain by extended continental crust. This preliminary interpretation of the troughs deep structure uses 3700 km of 1970s vintage seismic data, supplemented by gravity and magnetic data from the same surveys. The main seismic profile grid has a spacing of approximately 50 km. However, another survey shot in a zigzag pattern provides line spacing locally as close as a few kilometers.  Acoustic basement, characterized by a chaotic and indistinct seismic signature with rare, discontinuous steeply dipping reflections, is overlain by two main acousto-stratigraphic megasequences within the trough: (1) The post-rift section comprises flat-lying , continuous reflections and extends up to two seconds two-way travel time (TWT) below the water bottom. (2) The syn-rift section consists of moderately dipping semi-continuous reflections, separated by zones of chaotic reflections and diffractions. The reflection separating the syn- and post-rift packages is quite distinct, characterized by angular discordances and truncated reflections. No wells have penetrated the syn-rift package.  Seismic profiles in all orientations reveal tilted basement fault blocks . Many bounding faults are clearly listric. Half-graben form a series of syn-rift depocenters with up to 5 km of syn-rift fill.  Syn-rift depocenters appear to be elongate along the axis of the trough, suggesting rift-parallel bounding faults and orthogonal extension. However, no structures parallel or perpendicular to the trough axis have been recognized.  Most of the syn-rift depocenters are composed of two or more smaller "deeps".  Two rifting models provide alternative syn-rift structural interpretations: (1) Curvilinear faults, based on a model derived from the East African Rift where the tectonic transport direction has been shown to be oblique to the rift axis, define a series of half-graben. Accommodation zones and half-graben polarity switches are identified from profile and plan-view geometries. (2) Nearly rectilinear 110Â°_ and 020o -striking faults, based on orthogonal extension models, predominate. However, both of these trends are oblique to the rift axis contrary to predicted geometries.  "Transfer faults" provide a structural basis for the apparent compartmentalization the syn-rift isopach cells into the "deeps".  The data are insufficient to unequivocally support either model, although the orthogonal extension fault geometry better explains the distribution of the depocenters. Both interpretations, combined with limited basement dip information suggest that the structure underlying the Queensland Trough is the product of oblique rifting.  Extension is aligned obliquely to the trough at 110Â°, rather than perpendicular to the rift elongation at 065Â°. The proposed kinematics suggest that formation of the trough pre-dates either the Coral or Tasman Sea taphrogenesis.

Tags: Earth Sciences, GA Publication, Journal, Published_External, QLD
Organization: Geoscience Australia Data