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  • 1
    Language: English
    In: Nature, 11 August 2016, Vol.536(7615), pp.201-4
    Description: Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth's major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength--velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time.
    Keywords: Gulf of California ; South China Sea ; Velocity ; Magma;
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 2
    Language: English
    In: Geology, 02/01/2018, Vol.46(2), pp.191-192
    Description: Rift dynamics are controlled by a combination of local and far-field forces. These forces interact with the thermo-rheological rift configuration and thereby generate the characteristic normal faults, graben structures, and transfer zones documented in rifts and rifted margins worldwide. Classically,...
    Keywords: Plate Tectonics ; Geology ; Dynamics ; Upwelling ; Modelling ; Asthenosphere ; Ocean Models ; Upwelling ; Rifting ; Graben ; Wind Stress ; Rheological Properties ; Ocean Circulation ; Mathematical Models ; Forces (Mechanics) ; Asthenosphere ; Clear Cutting ; Rifting ; Upwelling ; Upwelling ; Upwelling;
    ISSN: 0091-7613
    E-ISSN: 19432682
    Source: CrossRef
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  • 3
    Language: English
    In: Geology, March, 2014, Vol.42(3), p.211(4)
    Description: Rifting between large continental plates results in either continental breakup and the formation of conjugate passive margins, or rift abandonment and a set of aborted rift basins. The nonlinear interaction between key parameters such as plate boundary configuration, lithospheric architecture, and extension geometry determines the dynamics of rift evolution and ultimately selects between successful or failed rifts. In an attempt to evaluate and quantify the contribution of the rift geometry, we analyze the Early Cretaceous extension between Africa and South America that was preceded by ~20-30 m.y. of extensive intracontinental rifting prior to the final separation between the two plates. While the South Atlantic and Equatorial Atlantic conjugate passive margins continued into seafloor-spreading mode, forming the South Atlantic Ocean basin, Cretaceous African intraplate rifts eventually failed soon after South America broke away from Africa. We investigate the spatiotemporal dynamics of rifting in these domains through a joint plate kinematic and three-dimensional forward numerical modeling approach, addressing (1) the dynamic competition of Atlantic and African extensional systems, (2) two-stage kinematics of the South Atlantic Rift System, and (3) the acceleration of the South America plate prior to final breakup. Oblique rifts are mechanically favored because they require both less strain and less force in order to reach the plastic yield limit. This implies that rift obliquity can act as selector between successful ocean basin formation and failed rifts, explaining the success of the highly oblique Equatorial Atlantic rift and ultimately inhibiting the formation of a Saharan Atlantic Ocean. We suggest that thinning of the last continental connection between Africa and South America produced a severe strength-velocity feedback responsible for the observed increase in South America plate velocity. doi: 10.1130/G35082.1
    Keywords: Faults (Geology) -- Research ; Geodynamics -- Research ; Geological Research
    ISSN: 0091-7613
    Source: Cengage Learning, Inc.
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  • 4
    In: Nature, 2016, p.1
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Nature Publishing Group
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  • 5
    Language: English
    In: Tectonophysics, Nov 11, 2013, Vol.607, p.65(15)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tecto.2013.06.029 Byline: Sascha Brune, Julia Autin Abstract: The Gulf of Aden provides an ideal setting to study oblique rifting since numerous structural data are available onshore and offshore. Recent surveys showed that the spatio-temporal evolution of the Gulf of Aden rift system is dominated by three fault orientations: displacement-orthogonal (WSW), rift-parallel (WNW) and an intermediate E-W trend. The oldest parts of the rift that are exposed onshore feature displacement-orthogonal and intermediate directions, whereas the subsequently active necking zone involves mainly rift-parallel faults. The final rift phase recorded at the distal margin is characterised by displacement-orthogonal and intermediate fault orientations. We investigate the evolution of the Gulf of Aden from rift initiation to break-up by means of 3D numerical experiments on lithospheric scale. We apply the finite element model SLIM3D which includes realistic, elasto-visco-plastic rheology and a free surface. Despite recent advances, 3D numerical experiments still require relatively coarse resolution so that individual faults are poorly resolved. We address this issue by proposing a simple post-processing method that uses the surface stress-tensor to evaluate stress regime (extensional, strike-slip, compressional) and preferred fault azimuth. The described method is applicable to any geodynamic model and easy to introduce. Our model reproduces the observed fault pattern of the Gulf of Aden and illustrates how multiple fault directions arise from the interaction of local and far-field tectonic stresses in an evolving rift system. The numerical simulations robustly feature intermediate faults during the initial rift phase, followed by rift-parallel normal faulting at the rift flanks and strike-slip faults in the central part of the rift system. Upon break-up, displacement-orthogonal as well as intermediate faults occur. This study corroborates and extends findings from previous analogue experiments of oblique rifting on lithospheric scale and allows new insights in the timing of fault successions of the Gulf of Aden and continental rifts in general. Article History: Received 5 October 2012; Revised 18 June 2013; Accepted 27 June 2013
    Keywords: Strike-slip Faults -- Analysis ; Strike-slip Faults -- Models ; Finite Element Method -- Analysis ; Finite Element Method -- Models ; Tectonics -- Analysis ; Tectonics -- Models
    ISSN: 0040-1951
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Tectonophysics, Sept 24, 2013, Vol.604, p.51(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tecto.2013.02.009 Byline: Sascha Brune, Anton A. Popov, Stephan V. Sobolev Keywords: Rifting; Continental break-up; Plume-lithosphere interaction; Lithosphere erosion; Numerical modeling; Tectonic forces Abstract: The arrival of a plume head at Earth's continental lithosphere is often considered to be an important factor for continental break-up. However, the impact of plume impingement on strength and duration of a rift remains unclear. In this study, we quantify the mechanical and thermal influence of a plume (i.e. lithosphere erosion) on continental break-up. To do that we apply the three-dimensional numerical code SLIM3D that features realistic elasto-visco-plastic rheology. We model the thermo-mechanical response of a segment of Earth's lithosphere that is affected both by extension as well as plume-related lithosphere erosion in order to evaluate the influence on the overall force budget. We find that lithosphere erosion leads to a moderate lithospheric strength reduction of several TN/m. In a force-limited environment, however, this strength reduction may have strong influence on the timing of continental break-up, or it may even control whether continental break-up takes place at all. Additional reduction of the lithospheric strength is likely due to the massive emplacement of dikes that follows intensive melting within the plume head. Article History: Received 5 March 2012; Revised 26 December 2012; Accepted 1 February 2013
    Keywords: Tectonics -- Analysis ; Lithosphere -- Analysis
    ISSN: 0040-1951
    Source: Cengage Learning, Inc.
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  • 7
    In: Journal of Geophysical Research: Solid Earth, August 2012, Vol.117(B8), pp.n/a-n/a
    Description: In many cases the initial stage of continental break‐up was and is associated with oblique rifting. That includes break‐up in the Southern and Equatorial Atlantic, separation from eastern and western Gondwana as well as many recent rift systems, like Gulf of California, Ethiopia Rift and Dead Sea fault. Using a simple analytic mechanical model and advanced numerical, thermomechanical modeling techniques we investigate the influence of oblique extension on the required tectonic force in a three‐dimensional setting. While magmatic processes have been already suggested to affect rift evolution, we show that additional mechanisms emerge due to the three‐dimensionality of an extensional system. Focusing on non‐magmatic rift settings, we find that oblique extension significantly facilitates the rift process. This is due to the fact that oblique deformation requires less force in order to reach the plastic yield limit than rift‐perpendicular extension. The model shows that in the case of two competing non‐magmatic rifts, with one perpendicular and one oblique to the direction of extension but otherwise having identical properties, the oblique rift zone is mechanically preferred and thus attracts more strain. Oblique extension facilitates the rift process in non‐magmatic settings Shearing a continent requires up to two times less force than rifting it An oblique rift zone attracts more strain than a competitive normal rift
    Keywords: Continental Break‐Up ; Mathematical Modeling ; Numerical Modeling ; Oblique Rifting ; Tectonic Forces
    ISSN: 0148-0227
    E-ISSN: 2156-2202
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  • 8
    Language: English
    In: Earth and Planetary Science Letters, June 15, 2015, Vol.420, p.66(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2015.03.032 Byline: Peter D. Clift, Sascha Brune, Javier Quinteros Abstract: Rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling yet basins on some continental margins experience anomalous subsidence events that postdate active extension. Deep basins on the northern margin of the South China Sea, notably the Baiyun Sag, show basement subsidence accelerating after [approximately equal to]21 Ma, postdating extension by several million years. We combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following Early Miocene monsoon intensification is a viable trigger for ductile flow after the cessation of active extension. This illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate-tectonic coupling. Author Affiliation: (a) Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA (b) EarthByte Group, School of Geosciences, University of Sydney, NSW 2006, Australia (c) German Research Centre for Geosciences GFZ, 14473 Potsdam, Germany Article History: Received 6 November 2014; Revised 12 March 2015; Accepted 15 March 2015 Article Note: (miscellaneous) Editor: A. Yin
    Keywords: Geophysics – Analysis ; Geophysics – Environmental Aspects ; Mantle (Geology) – Analysis ; Mantle (Geology) – Environmental Aspects ; Continental Margins – Analysis ; Continental Margins – Environmental Aspects ; Tectonics – Analysis ; Tectonics – Environmental Aspects ; Sediments (Geology) – Analysis ; Sediments (Geology) – Environmental Aspects
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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  • 9
    In: Geochemistry, Geophysics, Geosystems, August 2014, Vol.15(8), pp.3392-3415
    Description: Rifting involves complex normal faulting that is controlled by extension direction, reactivation of prerift structures, sedimentation, and dyke dynamics. The relative impact of these factors on the observed fault pattern, however, is difficult to deduce from field‐based studies alone. This study provides insight in crustal stress patterns and fault orientations by employing a laterally homogeneous, 3‐D rift setup with constant extension velocity. The presented numerical forward experiments cover the whole spectrum of oblique extension. They are conducted using an elastoviscoplastic finite element model and involve crustal and mantle layers accounting for self‐consistent necking of the lithosphere. Despite recent advances, 3‐D numerical experiments still require relatively coarse resolution so that individual faults are poorly resolved. This issue is addressed by applying a post processing method that identifies the stress regime and preferred fault azimuth at each surface element. The simple model setup results in a surprising variety of fault orientations that are solely caused by the three‐dimensionality of oblique rift systems. Depending on rift obliquity, these orientations can be grouped in terms of rift‐parallel, extension‐orthogonal, and intermediate normal fault directions as well as strike‐slip faults. While results compare well with analog rift models of low to moderate obliquity, new insight is gained in advanced rift stages and highly oblique settings. Individual fault populations are activated in a characteristic multiphase evolution driven by lateral density variations of the evolving rift system. In natural rift systems, this pattern might be modified by additional heterogeneities, surface processes, and dyke dynamics. 3‐D numerical rift models are conducted covering the entire obliquity spectrum A constant extension direction can generate multiphase fault orientations A characteristic evolution of fault patterns from rift to breakup is identified
    Keywords: Lithosphere Geodynamics ; Rifting ; Oblique Tectonics ; Numerical Modeling ; Stress ; Strain Partitioning
    ISSN: 1525-2027
    E-ISSN: 1525-2027
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  • 10
    Language: English
    In: Geology, 2014, Vol.42(12), p.1071(4)
    Description: Break-up-related extrusive magmatism, imaged in reflection seismic data as seaward-dipping reflectors (SDRs), extends symmetrically along the volcanic margins of the Atlantic Ocean. Recent research found distinct along-margin variations in the distribution of SDRs, and abundance of volcanic material was found to be spatially linked to transfer fault systems. These segmented the propagating rift that later developed into the ocean, and are interpreted as rift propagation barriers. Based on these observations, we develop a numerical model, which shows that rift-parallel mantle flow and locally enhanced rates of volcanism are the result of delays in rift propagation and segmented opening. Our model suggests that segmentation is one of the major factors in the distribution and localization of rift-related extrusive magmatism. We conclude that in addition to mantle temperature and inherited crustal structures (e.g., weaknesses from previous rift episodes), rift propagation delay plays an important role in the distribution of extrusive volcanism at volcanic passive margins by controlling the mantle flow beneath the rift axis. doi: 10.1130/G36085.1
    Keywords: Volcanism – Analysis ; Magmatism – Analysis
    ISSN: 0091-7613
    Source: Cengage Learning, Inc.
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