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  • 1
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    In:  Geophys. Res. Lett., Tokyo, Terra Scientific Publishing Company, vol. 18, no. 17, pp. 1747-1750, pp. 8010, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1991
    Keywords: Elasticity ; Inelastic ; Plate tectonics ; GRL ; Dziewonski
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  • 2
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    In:  Earth planet. Sci. Lett., Luxembourg, Conseil de l'Europe, vol. 225, no. 1-2, pp. 177-189, pp. L09610, (ISSN: 1340-4202)
    Publication Date: 2004
    Keywords: Rheology ; Inelastic ; ConvolutionE ; Plate tectonics ; Gravimetry, Gravitation ; EPSL ; FLORENZO
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  • 3
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    In:  Geophysical Journal International, New York, Scientific American, vol. 165, no. 3, pp. 1041-1057, pp. B11404, (ISSN: 1340-4202)
    Publication Date: 2006
    Keywords: Plate tectonics ; ConvolutionE ; Geodesy ; African ; rift, ; Cenozoic ; plate ; motions, ; hotspots, ; mantle ; plumes, ; NUVEL-1, ; tectonic ; plates, ; thermal ; convection, ; Quere ; GJI
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  • 4
    Publication Date: 2016-12-25
    Description: Efforts to extract information about climate and tectonics from topography commonly assume that river networks are static. Drainage divides can migrate through time, however, and recent work has shown that divide mobility can potentially induce changes in river profiles comparable to changes caused by variation in rock uplift, climate, or rock properties. We use 1D river profile and 2D landscape evolution simulations to evaluate how mobile divides influence the interpretation of river profiles in tectonically active settings. We define a non-dimensional divide migration number, N Dm , as the ratio of the timescale of channel profile response to a change in drainage area ( T dA ) to the timescale of divide migration ( T Dm ). In simulations of headward divide migration, N Dm is much less than unity with no measurable perturbation of channel profiles. Only in simulations configured to induce rapid lateral divide migration are there occasional large stream capture events and zones where localized drainage area loss is fast enough to support N Dm values near unity. The rapid response of channel profiles to changes in drainage area ensures that under most conditions profiles maintain quasi-equilibrium forms and thus generally reflect spatio-temporal variation in rock uplift, climate, or rock properties even during active divide migration. This implies that channel profile form may not reliably record divide mobility, so we evaluate alternate metrics of divide mobility. In our simulations and an example in Taiwan, we find that simple measures of cross-divide contrasts in topography are more robust metrics of divide mobility than measures of drainage network topology.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2016-11-03
    Description: Comparison of plate convergence with the timing and magnitude of upper-crustal shortening in collisional orogens indicates both shortening deficits (200-1700 km) and significant (10-40%) plate deceleration during collision, the cause(s) for which remain debated. The Greater Caucasus Mountains, which result from post-collisional Cenozoic closure of a relict Mesozoic back-arc basin on the northern margin of the Arabia-Eurasia collision zone, help reconcile these debates. Here we use U-Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now-consumed Mesozoic back-arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persisted until at least the Miocene. Maximum basin width was likely ~350-400 km. We propose that closure of the back-arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia-Eurasia collision along the Bitlis-Zagros suture, eventually leading to ~5 Ma (hard) collision between the Lesser Caucasus arc and the Scythian platform to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision. Post-collisional subduction of such small (10 2 -10 3  km wide) relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting, although such shortening is easily missed if it occurs along structures hidden within flysch/slate belts. Relict-basin closure is likely typical in continental collisions in which the colliding margins are either irregularly shaped or rimmed by extensive back-arc basins and fringing arcs, such as those in the modern South Pacific.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2014-10-08
    Description: The Greater Caucasus Mountains, due to their youth (~5 Ma), provide an opportunity for insight into the early stages of orogen development during continent-continent collision. However, their recent tectonic evolution and first-order architecture remain unclear. Here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity, geodetic strain, bedrock geology and foreland-basin structure. We find that the range contains four zones along strike that differ in structural architecture, topography, and first-order tectonic history. In particular, two south-directed, singly-vergent zones at the western and eastern tips of the orogen are separated by both a central doubly-vergent zone that is dominated by north-directed deformation, and an eastern doubly-vergent zone in which south-directed thrusting dominates. We hypothesize that the along-strike changes in vergence and locus of deformation reflects different stages in the development of a doubly-vergent orogen, with the tips of the range preserving an early, singly-vergent form and the center recording a more advanced orogen. The differences between the two-doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the Greater and Lesser Caucasus orogens, which initiated at ~5 Ma.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2011-10-01
    Description: Changes in African topography driven by mantle convection Nature Geoscience 4, 707 (2011). doi:10.1038/ngeo1235 Authors: Robert Moucha & Alessandro M. Forte The topography of the African continent is characterized by large-scale extensional features such as the East African Rift, widespread volcanic activity, and anomalously subsided basins and uplifted domes. These enigmatic surface features have long suggested that the African continent is shaped by significant dynamic forcing originating in the underlying mantle. Here we simulate mantle convection backwards in time to reconstruct the evolution of dynamic topography of Africa over the past 30 million years. We show that the current high topography of the East African Rift system is due to the southward propagation of a topographic swell that encompassed the western margin of Arabia and the Afar region before 30 million years ago. We suggest that this dominant swell formed in response to the upwelling of the African superplume and the relative northward motion of the African tectonic plate over it. We also find that the adjacent Congo Basin has gradually subsided over the same time period in response to convective drawdown in the mantle. We conclude that much of Africa’s recent geological history is driven by buoyancy forces in the mantle. Our findings have important implications for African volcanism, erosion, sediment transport and river-basin drainage patterns.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 8
    Publication Date: 2011-10-14
    Description: In order to test the hypothesis that seismic anisotropy in the lowermost mantle is caused by the development of a post-perovskite lattice preferred orientation, and that anisotropy can thus be used as a probe of the dynamics of the mantle's lower boundary layer, an integrated model of texture generation in D″ is developed. This is used to predict the elastic anisotropy of the lowermost mantle as probed by global anisotropic tomographic inversions. The model combines the current 3D mantle flow field with simulations of the deformation of post-perovskite polycrystalline aggregates. Different descriptions of single crystal plasticity can lead to model results which are anti-correlated to each other. In models where post-perovskite deformation is accommodated by dislocations moving on (010) or (100), patterns of anisotropy are approximately correlated with the results of tomographic inversions. On the other hand, in models where dislocations move on (001) patterns of anisotropy are nearly anti-correlated with tomographic inversions. If all the seismic anisotropy in D″ extracted from global anisotropic inversions is due to the presence of a lattice preferred orientation in post-perovskite in the lowermost mantle, and if the results of the tomographic inversions are not strongly biased by the sampling geometries, these results suggest that, in contrast to ideas based on the 1D anisotropic signal, deformation of post-perovskite in the lowermost mantle may be accommodated by dislocations moving on (010) or (100). Alternatively, a significant portion of the anisotropic signal may be caused by mechanisms other than the alignment of post-perovskite crystals.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2012-11-02
    Description: SUMMARY The precession and obliquity frequencies of the Earth’s rotational motion are functions of the dynamic ellipticity of the Earth’s gravitational figure, and this connection has provided a novel bridge between studies of palaeoclimate and geodynamics. In particular, analyses of tuned climate proxy records have yielded bounds on the mean relative perturbation in dynamic ellipticity over both the last 3 Myr and 25 Myr that are less than ∼3 per cent of the non-hydrostatic component of the ellipticity. We demonstrate that this apparent consistency actually defines an important geophysical enigma. Over the last 3 Myr, changes in the Earth’s figure are likely dominated by ice age forcings—in this case, a small perturbation to dynamic ellipticity implies significant isostatic compensation of the ice-ocean surface mass loads and, hence, a relatively low mantle viscosity. In contrast, over the last 25 Myr, changes in the Earth’s long-wavelength gravitational form are likely dominated by mantle convective flow, and in this case, the small perturbation to dynamic ellipticity implies sluggish convection and a relatively high mantle viscosity. There are at least four possible routes to resolving this enigma: The viscosity in the Earth’s mantle is transient (i.e. dependent on the timescale of the applied forcing), tidal dissipation changed in a manner between the last 3 Myr and 25 Myr that was sufficient to resolve the issue, the observationally inferred bounds are unrealistically restrictive, or earth models exist in which the ice age and convection effects approximately cancel leading to no net perturbation. In this paper, we compute a suite of numerical predictions of ice age and convection-induced perturbations to the dynamic ellipticity to illustrate the enigma described above.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
    Publication Date: 2012-04-15
    Description: SUMMARY We propose an innovative approach to mapping CMB topography from seismic P -wave traveltime inversions: instead of treating mantle velocity and CMB topography as independent parameters, as has been done so far, we account for their coupling by mantle flow, as formulated by Forte & Peltier. This approach rests on the assumption that P data are sufficiently sensitive to thermal heterogeneity, and that compositional heterogeneity, albeit important in localized regions of the mantle (e.g. within the D ″ region), is not sufficiently strong to govern the pattern of mantle-wide convection and hence the CMB topography. The resulting tomographic maps of CMB topography are physically sound, and they resolve the known discrepancy between images obtained from classic tomography on the basis of core-reflected and core-refracted seismic phases. Since the coefficients of mantle velocity structure are the only free parameters of the inversion, this joint tomography–geodynamics approach reduces the number of parameters; nevertheless the corresponding mantle models fit the seismic data as well as the purely seismic ones.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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