FrOG Technology Pty Ltd

Canberra, Australia

FrOG Technology Pty Ltd

Canberra, Australia
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Direen N.G.,University of Tasmania | Direen N.G.,University of Adelaide | Direen N.G.,FrOG Technology Pty. Ltd. | Stagg H.M.J.,Geoscience Australia | And 2 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2011

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. Copyright 2011 by the American Geophysical Union.

Maloney D.,Durham University | Sargent C.,Durham University | Direen N.G.,University of Tasmania | Direen N.G.,FrOG Technology Pty Ltd | And 2 more authors.
Solid Earth | Year: 2011

Vintage 2-D (two-dimensional) seismic reflection surveys from the sparsely explored Mentelle Basin (western Australian margin) have been reprocessed and integrated with a recent high-quality 2-D seismic survey and stratigraphic borehole data. Interpretation of these data sets allows the internal geometry of the Mentelle Basin fill and depositional history to be reanalysed and new insights into its formation revealed. Basin stratigraphy can be subdivided into several seismically defined megasequences separated by major unconformities related to both breakup between India- Madagascar and Australia-Antarctica in the Valanginian- Late Hauterivian and tectonically-driven switches in deposition through the Albian. Resting on the Valanginian-Late Hauterivian breakup unconformity are several kilometre-scale mounded structures that formed during Late Jurassic to Early Cretaceous extension. These have previously been interpreted as volcanic edifices although direct evidence of volcanic feeder systems is lacking. An alternative interpretation is that these features may be carbonate build-ups. The latter interpretation carries significant climatic ramifications since carbonate build-ups would have formed at high palaeolatitude, ∼60° S. Soon after breakup, initial subsidence resulted in a shallow marine environment and deposition of Barremian-Aptian silty-sandy mudstones. As subsidence continued, thick successions of Albian ferruginous black clays were deposited. Internally, seismic megasequences composed of successions of black clays show previously unresolved unconformities, onlapping and downlapping packages, which reflect a complex depositional, rifting and subsidence history at odds with their previous interpretation as open marine sediments. Southwestwards migration of the Kerguelen hotspot led to thermal contraction and subsidence to the present day water depth (∼3000 m). This was accompanied by Turonian- Santonian deposition of massive chalk beds, which are unconformably overlain by pelagic Palaeocene-Holocene sediments. This substantial unconformity is related to the diachronous breakup and onset of slow spreading between Australia and Antarctica, which may have led to the reactivation and inversion of basement faults and was followed by rapid seafloor spreading from the Middle Eocene to the present. © 2011 Author(s).

Dumont J.F.,ESPOL | Dumont J.F.,IRD Montpellier | Santana E.,ESPOL | Bonnardot M.-A.,French National Center for Scientific Research | And 4 more authors.
Geological Society Memoir | Year: 2014

The pacific border of the South American plate presents a more or less symmetrical sinuosity, with a central concave curvature (the Arica Angle located between two side rays along Chile and Peru) and ending in convex arcs (the Patagonian and Talara arcs, respectively). The width of the continental and coastal margins varies significantly according to the geometry of the border. The continental margin of Ecuador corresponds to the northern part of the Talara Arc. Three different segments showing different coastal geomorphology and continental platform characteristics are identified from north to south: the northern segment (Mataje River-Galera Point) shows a wide continental shelf and slope, the upper subducted slab of the subduction plane presents a low dip; the central segment (Galera Point- Santa Elena) stands in front of the Carnegie Ridge, and presents a moderate uplift in the Manta Peninsula, in front of the Carnegie Ridge, and the upper subduction plane is subhorizontal; the southern segment includes the side and inner coasts of the Gulf of Guayaquil, below the gulf the subduction plane shows a low dip. A comparison with published 3D numerical modelling of curved subduction suggests that the geometry of the continental boundary has a significant effect on uplift or subsidence along the continental margin. Also, the subduction of asperities in the trench, such as the Carnegie Ridge, may change the coastal motion from subsiding to uplifting, as is observed in the Esmeraldas area. There is no clear evidence of a shelf developed during the Last Glacial Maximum (LGM) sea-level lowstand, probably due to the vertical motion - uplift or subsidence - observed all along the coastal margin. © The Geological Society of London 2014.

Direen N.G.,University of Tasmania | Direen N.G.,FrOG Technology Pty Ltd | Symonds P.A.,Geoscience Australia | Norton I.O.,University of Texas at Austin
Geological Society Special Publication | Year: 2013

We present a synthesis based on the interpretation of two pairs of deep seismic reflection crustal sections within the Southern Rift System (SRS) separating Australia and Antarctica. One pair of sections is from the conjugate margins between the Great Australian Bight (GAB) and Wilkes Land, in the central sector of the SRS, which broke up in the Campanian. The second pair of conjugate sections is located approximately 400 km further east, between the Otway Basin and Terre Adélie, which probably broke up in Maastrichtian time. Interpretations are based on an integrated synthesis of deep multi-channel seismic, gravity and magnetic data, together with sparse sonobuoy and dredging information, and the conjugate sections are presented with the oceanic crust removed beyond the continent-ocean boundary (COB). At first order, both conjugate pairs show a transition from thinned continental crust, through a wide and internally complex continent-ocean transition zone (COTZ), which shows features in common with magma-poor rifted margins worldwide, such as basement ridges interpreted as exhumed subcontinental mantle. In the central GAB sector, the COTZ is symmetric around the point of break-up and displays a pair of mantle ridges, one on each margin, outboard of which lies a deep-water rift basin. Break-up has occurred in the centre of this basin in this sector of the SRS. In contrast, the Terre Adélie margin is nearly 600 km wide and shows an abandoned crustal megaboudin, the Adélie Rift Block. This block is underlain by interpreted middle crust, and appears to have a mantle ridge structure inboard, as well as an outboard exhumed mantle complex from which mylonitized harzburgite has been dredged. The conjugate margin of the Beachport Sub-basin is relatively narrow (c. 100 km wide) and does not appear to contain an exhumed mantle ridge, as observed along strike in the GAB. These observations from a single rift spreading compartment show that radically different breakup symmetries and margin architectures can result from an essentially symmetric rifting process involving multiple, paired detachment systems. This indicates the need for caution in interpreting causative mechanisms of rifting from limited conjugate sections in other rifts. We speculate that the underlying crustal composition, rheology and structural preconditioning play a significant role in partitioning strain during the transition to break-up. © The Geological Society of London 2013.

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