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Now showing items 1 - 12 of 12

  • Australian plate motion and topography linked to fossil New Guinea slab below Lake Eyre

    Schellart, W.P.   Spakman, W.  

    Highlights • Identification of ∼71–50 Ma subduction zone at northern edge of Australian plate. • Subduction termination coincides with obduction in New Guinea and plate slowdown. • Sinking slab caused southward migration of dynamic topography subsidence over plate. • Fossil slab now below central-SE Australia causing Eyre–Murray–Darling depression. • Dynamic topography evolution couples geological processes to a mantle reference frame. Abstract Unravelling causes for absolute plate velocity change and continental dynamic topography change is challenging because of the interdependence of large-scale geodynamic driving processes. Here, we unravel a clear spatio-temporal relation between latest Cretaceous–Early Cenozoic subduction at the northern edge of the Australian plate, Early Cenozoic Australian plate motion changes and Cenozoic topography evolution of the Australian continent. We present evidence for a ∼4000 km wide subduction zone, which culminated in ophiolite obduction and arc-continent collision in the New Guinea–Pocklington Trough region during subduction termination, coinciding with cessation of spreading in the Coral Sea, a ∼5 cm/yr decrease in northward Australian plate velocity, and slab detachment. Renewed northward motion caused the Australian plate to override the sinking subduction remnant, which we detect with seismic tomography at 800–1200 km depth in the mantle under central-southeast Australia at a position predicted by our absolute plate reconstructions. With a numerical model of slab sinking and mantle flow we predict a long-wavelength subsidence (negative dynamic topography) migrating southward from ∼50 Ma to present, explaining Eocene–Oligocene subsidence of the Queensland Plateau, ∼330 m of late Eocene–early Oligocene subsidence in the Gulf of Carpentaria, Oligocene–Miocene subsidence of the Marion Plateau, and providing a first-order fit to the present-day, ∼200 m deep, topographic depression of the Lake Eyre Basin and Murray–Darling Basin. We propound that dynamic topography evolution provides an independent means to couple geological processes to a mantle reference frame. This is complementary to, and can be integrated with, other approaches such as hotspot and slab reference frames.
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  • Subduction-induced mantle convection on Earth: Poloidal versus toroidal flow

    Schellart, W.P.   Freeman, J.   Stegman, D.R.  

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  • Analogue modeling of arc and backarc deformation in the New Hebrides arc and North Fiji Basin

    Schellart, W.P.   Lister, G.S.   Jessell, M.W.  

    In most backarc basins, extension is perpendicular to the arc. Thus individual spreading ridges extend approximately parallel to the arc. In the North Fiji Basin, however, several ancient and active spreading ridges strike 70degrees-90degrees to the New Hebrides are. These high-angle spreading ridges relocated southward during the asymmetric opening of the North Fiji Basin. We have simulated the structural development of the North Fiji Basin and the New Hebrides arc with scaled analogue models, and the results have inspired us to come to several tentative conclusions. We interpret the orientation of the high-angle spreading ridges to be related to the asymmetric opening of the backarc basin around a hinge, where they form close to the hinge. Relocation of these spreading ridges is most likely related to subduction of the West Torres Plateau along the New Hebrides Trench. This resulted in localized collision, retarded rollback of the subducting slab along the northwest corner of the trench, and reduced extension and shearing in the northwest corner of the North Fiji Basin. Backarc extension continued in the rest of the North Fiji Basin owing to continued rollback of the southern part of the subducting slab. Here, active extension was separated from the slightly or nonextending northwest corner by a zone striking at high angle to the New Hebrides arc, i.e., the Hazel Holme extensional zone. Moreover, impingement of the d'Entrecasteaux Ridge into the overriding plate led to local deformation and fragmentation of the are.
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  • The role of the East Asian active margin in widespread extensional and strike-slip deformation in East Asia

    Schellart, W.P.   Lister, G.S.  

    East Asia is a region of widespread deformation, dominated by normal and strike-slip faults. Deformation has been interpreted to result from extrusion tectonics related to the India-Eurasia collision, which started in the Early Eocene. In East and SE China, however, deformation started earlier than the collision (latest Cretaceous to Palaeocene), suggesting that extrusion tectonics is not the (only) driving mechanism for East Asia deformation. It is suggested that the East Asian active margin has influenced deformation in East Asia significantly. Along the margin, Cenozoic back-arc extension took place behind several adjoining arcs, implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge-line. We show that extension took place along a c. 7400 km long stretch of the East Asian margin during most of the Cenozoic. Physical models are presented simulating overriding plate collapse and back-are extension. The models reproduce important aspects of the strain field in East Asia. For geometrical and theological conditions scaled to represent East Asia, modelling shows that the active margin can be held responsible for deformation in East Asia as far west as the Baikal rift zone, located c. 3300 km from the margin.
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  • Global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones

    Schellart, W.P.   Rawlinson, N.  

    The maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on Earth, with some subduction zone segments producing giant subduction zone thrust earthquakes (e.g. Chile, Alaska, Sumatra-Andaman, Japan) and others producing relatively small earthquakes (e.g. Mariana, Scotia). Here we show how such variability might depend on various subduction zone parameters. We present 24 physical parameters that characterize these subduction zones in terms of their geometry, kinematics, geology and dynamics. We have investigated correlations between these parameters and the maximum recorded moment magnitude ( MW) for subduction zone segments in the period 1900-June 2012. The investigations were done for one dataset using a geological subduction zone segmentation (44 segments) and for two datasets (rupture zone dataset and epicenter dataset) using a 200 km segmentation (241 segments). All linear correlations for the rupture zone dataset and the epicenter dataset (| R| = 0.00-0.30) and for the geological dataset (| R| = 0.02-0.51) are negligible-low, indicating that even for the highest correlation the best-fit regression line can only explain 26% of the variance. A comparative investigation of the observed ranges of the physical parameters for subduction segments with MW > 8.5 and the observed ranges for all subduction segments gives more useful insight into the spatial distribution of giant subduction thrust earthquakes. For segments with MW > 8.5 distinct (narrow) ranges are observed for several parameters, most notably the trench-normal overriding plate deformation rate ( vOPDperp, i.e. the relative velocity between forearc and stable far-field backarc), trench-normal absolute trench rollback velocity ( vTperp), subduction partitioning ratio ( vSPperp/ vSperp, the fraction of the subduction velocity that is accommodated by subducting plate motion), subduction thrust dip angle ( deltaST), subduction thrust curvature ( CST), and trench curvature angle ( alphaT). The results indicate that MW > 8.5 subduction earthquakes occur for rapidly shortening to slowly extending overriding plates (-3.0 les vOPDperp les 2.3 cm/yr), slow trench velocities (-2.9 les vTperp les 2.8 cm/yr), moderate to high subduction partitioning ratios ( vSPperp/ vSperp les 0.3-1.4), low subduction thrust dip angles ( deltaST les 30deg), low subduction thrust curvature ( CST les 2.0 times 10 -13 m -2) and low trench curvature angles (-6.3deg les alphaT les 9.8deg). Epicenters of giant earthquakes with MW > 8.5 only occur at trench segments bordering overriding plates that experience shortening or are neutral ( vOPDperp les 0), suggesting that such earthquakes initiate at mechanically highly coupled segments of the subduction zone interface that have a relatively high normal stress (deviatoric compression) on the interface (i.e. a normal stress asperity). Notably, for the three largest recorded earthquakes (Chile 1960, Alaska 1964, Sumatra-Andaman 2004) the earthquake rupture propagated from a zone of compressive deviatoric normal stress on the subduction zone interface to a region of lower normal stress (neutral or deviatoric tension). Stress asperities should be seen separately from frictional asperities that result from a variation in friction coefficient along the subduction zone interface. We have developed a global map in which individual subduction zone segments have been ranked in terms of their predicted capability of generating a giant subduction zone earthquake ( MW > 8.5) using the six most indicative subduction zone parameters ( vOPDperp, vTperp, vSPperp/ vSperp, deltaST, CST and alphaT). We identify a number of subduction zones and segments that rank highly, which implies a capability to generate MW > 8.5 earthquakes. These include Sunda, North Sulawesi, Hikurangi, Nankai-northern Ryukyu, Kamchatka-Kuril-Japan, Aleutians-Alaska, Cascadia, Mexico-Central America, South America, Lesser Antilles, western Hellenic and Makran. Several subduction segments have a low score, most notably Scotia, New Hebrides and Mariana. [All rights reserved Elsevier].
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  • Comment on “The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle” by W.P. Schellart

    Carlo Doglioni  

    The Schellart's [Schellart, W.P., 2007, The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle. Tectonophysics, 445, 363-372.] paper uses slab dip and upper plate extension for testing the westward drift. His analysis and discussion are misleading for the study of the net rotation of the lithosphere since the first 125 km of subduction zones are sensitive also to other parameters such upper plate thickness, geometry and obliquity of the subduction zone with respect to the convergence direction. The deeper (> 125 km) part cannot easily be compared as well because E- or NE-directed subduction zones have seismic gaps between 270-630 km. Moreover the velocity of subduction hinge cannot be precisely estimated and it does not equal to backarc spreading due to accretionary prism growth and asthenospheric intrusion at the subduction hinge. It is shown here that hinge migration in the upper plate or lower plate reference frames supports a general global polarization of the lithosphere in agreement with the westward drift of the lithosphere. The W-directed subduction zones appear controlled by the slab-mantle interaction with slab retreat imposed by the eastward mantle flow. The opposite E-NE-directed subduction zones seem rather mainly controlled by the convergence rate, plus density, thickness and viscosity of the upper and lower plates. Finally, the geological and geophysical asymmetries recorded along subduction and rift zones as a function of their polarity with respect to the tectonic mainstream are not questioned in the Schellart's paper, but they rather represent the basic evidence for the westward drift of the lithosphere.
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  • Comment on "The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle" by WP Schellart RID D-2620-2009

    Doglioni, Carlo  

    The Schellart's [Schellart, W.P., 2007, The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle. Tectonophysics, 445, 363-372.] paper uses slab dip and upper plate extension for testing the westward drift. His analysis and discussion are misleading for the study of the net rotation of the lithosphere since the first 125 km of subduction zones are sensitive also to other parameters such upper plate thickness, geometry and obliquity of the subduction zone with respect to the convergence direction. The deeper (> 125 km) part cannot easily be compared as well because E- or NE-directed subduction zones have seismic gaps between 270-630 km. Moreover the velocity of subduction hinge cannot be precisely estimated and it does not equal to backarc spreading due to accretionary prism growth and asthenospheric intrusion at the subduction hinge. It is shown here that hinge migration in the upper plate or lower plate reference frames supports a general global polarization of the lithosphere in agreement with the westward drift of the lithosphere. The W-directed subduction zones appear controlled by the slab-mantle interaction with slab retreat imposed by the eastward mantle flow. The opposite E-NE-directed subduction zones seem rather mainly controlled by the convergence rate, plus density, thickness and viscosity of the upper and lower plates. Finally, the geological and geophysical asymmetries recorded along subduction and rift zones as a function of their polarity with respect to the tectonic mainstream are not questioned in the Schellart's paper, but they rather represent the basic evidence for the westward drift of the lithosphere. (c) 2008 Elsevier B.V. All rights reserved.
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  • Special Paper 383: Orogenic curvature: Integrating paleomagnetic and structural analyses Volume 383 || Tectonic models for the formation of arc-shaped convergent zones and backarc basins

    Schellart, W.P.  

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  • Comment on “The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle” by W.P. Schellart

    Carlo Doglioni  

    The Schellart's [Schellart, W.P., 2007, The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle. Tectonophysics, 445, 363–372.] paper uses slab dip and upper plate extension for testing the westward drift. His analysis and discussion are misleading for the study of the net rotation of the lithosphere since the first 125 km of subduction zones are sensitive also to other parameters such upper plate thickness, geometry and obliquity of the subduction zone with respect to the convergence direction. The deeper (> 125 km) part cannot easily be compared as well because E- or NE-directed subduction zones have seismic gaps between 270–630 km. Moreover the velocity of subduction hinge cannot be precisely estimated and it does not equal to backarc spreading due to accretionary prism growth and asthenospheric intrusion at the subduction hinge. It is shown here that hinge migration in the upper plate or lower plate reference frames supports a general global polarization of the lithosphere in agreement with the westward drift of the lithosphere. The W-directed subduction zones appear controlled by the slab–mantle interaction with slab retreat imposed by the eastward mantle flow. The opposite E-NE-directed subduction zones seem rather mainly controlled by the convergence rate, plus density, thickness and viscosity of the upper and lower plates. Finally, the geological and geophysical asymmetries recorded along subduction and rift zones as a function of their polarity with respect to the tectonic mainstream are not questioned in the Schellart's paper, but they rather represent the basic evidence for the westward drift of the lithosphere.
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  • Comment on: "Evolution of the slab bending radius and bending dissipation in three-dimensional subduction models with variable slab to upper mantle viscosity ratio" by WP Schellart, Earth and Planetary Science Letters 288 (2009) 309-319

    Buffett, Bruce A.  

    A recent paper (Schellart, 2009) presents a suite of laboratory experiments on subduction to explore the role of slab bending and the associated dissipation. This work builds on previous experiments and provides a welcome complement to current computational efforts. Much of the recent progress is reviewed by Schellart (2009). However, the description of previous studies by Buffett (2006) and Buffett and Rowley (2006) contains a number of inaccuracies. The goal of this comment is to clarify several points and to suggest ways that recent theoretical results might be used to interpret the experiments. (C) 2010 Elsevier B.V. All rights reserved.
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  • Comment on: “Evolution of the slab bending radius and bending dissipation in three-dimensional subduction models with variable slab to upper mantle viscosity ratio” by W.P. Schellart, Earth and Planetary Science Letters 288 (2009) 309–319

    Bruce A. Buffett  

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  • Comment on: “Evolution of the slab bending radius and bending dissipation in three-dimensional subduction models with variable slab to upper mantle viscosity ratio” by W.P. Schellart, Earth and Planetary Science Letters 288 (2009) 309–

    Bruce A. Buffett  

    A recent paper (Schellart, 2009) presents a suite of laboratory experiments on subduction to explore the role of slab bending and the associated dissipation. This work builds on previous experiments and provides a welcome complement to current computational efforts. Much of the recent progress is reviewed by Schellart (2009). However, the description of previous studies by Buffett (2006) and Buffett and Rowley (2006) contains a number of inaccuracies. The goal of this comment is to clarify several points and to suggest ways that recent theoretical results might be used to interpret the experiments.
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