1,721,033 research outputs found
The uplift of the East Africa - Arabia swell
No full textThe East Africa - Arabia topographic swell is an anomalously high-elevation region of ~4000 km long (from southern Ethiopia to Jordan) and ~ 1500 km wide (from Egypt to Saudi Arabia) extent. The swell is dissected by the Main Ethiopian, Red Sea, and Gulf of Aden rifts, and characterized by widespread basaltic volcanic deposits emplaced from the Eocene to the present. Geochemical and geophysical data confirm the involvement of mantle processes in swell formation; however, they have not been able to fully resolve some issues, e.g., regarding the number and location of plumes and uplift patterns. This study addresses these questions and provides a general evolutionary model of the region by focusing on the present topographic configuration through a quantitative analysis and correlating long and intermediate wavelength features with mantle and rifting processes. Moreover, the isostatic and dynamic components of topography have been evaluated considering a range of seismic tomographic models for the latter. When interpreted jointly with geological data including volcanic deposits, the constraints do imply causation by a single process which shaped the past and present topography of the study area: the upwelling of the Afar superplume. Once hot mantle material reached the base of the lithosphere below the Horn of Africa during the Late Eocene, the plume flowed laterally toward the Levant area guided by preexisting discontinuities in the Early Miocene. Plume material reached the Anatolian Plateau in the Late Miocene after slab break-off and the consequent formation of a slab window. During plume material advance, buoyancy forces led to the formation of the topographic swell and tilting of the Arabia Peninsula. The persistence of mantle support beneath the study area for tens of million years also affected the formation and evolution of the Nile and Euphrates-Tigris fluvial networks. Subsequently, surface processes, tectonics, and volcanism partly modified the initial topography and shaped the present-day landscape
Mantle convection in the Middle East: Reconciling Afar upwelling, Arabia indentation and Aegean trench rollback
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Long-term, deep-mantle support of the Ethiopia-Yemen Plateau
No full textEthiopia is a key site to investigate the interactions between mantle dynamics and surface processes because of the presence of the Main Ethiopian Rift (MER), Cenozoic continental flood basalt volcanism, and plateau uplift. The role of mantle plumes in causing Ethiopia's flood basalts and tectonics has been commonly accepted. However, the location and number of plumes and their impact on surface uplift are still uncertain. Here we present new constraints on the geological and topographic evolution of the Ethiopian Plateau (NW Ethiopia) prior to and after the emplacement of the large flood basalts (40-20 Ma). Using geological information and topographic reconstructions, we show that the large topographic dome that we see today is a long-term feature, already present prior to the emplacement of the flood basalts. We also infer that large-scale doming operated even after the emplacement of the flood basalts. Using a comparison with the present-day topographic setting, we show that an important component of the topography has been and is presently represented by a residual, nonisostatic, dynamic contribution. We conclude that the growth of the Ethiopian Plateau is a long-term, probably still active, dynamically supported process. Our arguments provide constraints on the processes leading to the formation of one of the largest igneous plateaus on Earth
Assessing plate reconstruction models using plate driving force consistency tests
No full textAbstract Plate reconstruction models are constructed to fit constraints such as magnetic anomalies, fracture zones, paleomagnetic poles, geological observations and seismic tomography. However, these models do not consider the physical equations of plate driving forces when reconstructing plate motion. This can potentially result in geodynamically-implausible plate motions, which has implications for a range of work based on plate reconstruction models. We present a new algorithm that calculates time-dependent slab pull, ridge push (GPE force) and mantle drag resistance for any topologically closed reconstruction, and evaluates the residuals—or missing components—required for torques to balance given our assumed plate driving force relationships. In all analyzed models, residual torques for the present-day are three orders of magnitude smaller than the typical driving torques for oceanic plates, but can be of the same order of magnitude back in time—particularly from 90 to 50 Ma. Using the Pacific plate as an example, we show how our algorithm can be used to identify areas and times with high residual torques, where either plate reconstructions have a high degree of geodynamic implausibility or our understanding of the underlying geodynamic forces is incomplete. We suggest strategies for plate model improvements and also identify times when other forces such as active mantle flow were likely important contributors. Our algorithm is intended as a tool to help assess and improve plate reconstruction models based on a transparent and expandable set of a priori dynamic constraints
Slab interactions in 3-D subduction settings: The Philippine Sea Plate region
No full textThe importance of slab–slab interactions is manifested in the kinematics and geometry of the Philippine Sea Plate and western Pacific subduction zones, and such interactions offer a dynamic basis for the first-order observations in this complex subduction setting. The westward subduction of the Pacific Sea Plate changes, along-strike, from single slab subduction beneath Japan, to a double-subduction setting where Pacific subduction beneath the Philippine Sea Plate occurs in tandem with westward subduction of the Philippine Sea Plate beneath Eurasia. Our 3-D numerical models show that there are fundamental differences between single slab systems and double slab systems where both subduction systems have the same vergence. We find that the observed kinematics and slab geometry of the Pacific–Philippine subduction can be understood by considering an along-strike transition from single to double subduction, and is largely independent from the detailed geometry of the Philippine Sea Plate. Important first order features include the relatively shallow slab dip, retreating/stationary trenches, and rapid subduction for single slab systems (Pacific Plate subducting under Japan), and front slabs within a double slab system (Philippine Sea Plate subducting at Ryukyu). In contrast, steep to overturned slab dips, advancing trench motion, and slower subduction occurs for rear slabs in a double slab setting (Pacific subducting at the Izu–Bonin–Mariana). This happens because of a relative build-up of pressure in the asthenosphere beneath the Philippine Sea Plate, where the asthenosphere is constrained between the converging Ryukyu and Izu–Bonin–Mariana slabs. When weak back-arc regions are included, slab–slab convergence rates slow and the middle (Philippine) plate extends, which leads to reduced pressure build up and reduced slab–slab coupling. Models without back-arcs, or with back-arc viscosities that are reduced by a factor of five, produce kinematics compatible with present-day observations
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Impacts of lithospheric rheology on surface topography
Full text linkDynamic topography is the surface expression of asthenospheric convection by means of vertical deflection of the lithosphere and includes the topographic responses to mantle flow patterns such as upwelling plumes and downwelling slabs. Dynamic topography depends on the properties of the convective anomaly, but the modulation due to properties of the lithosphere are less well understood. This work aims to investigate the impacts of the lithosphere through numerical and analytical approaches using purely viscous rheology and compare our results with analogue experiments. Unlike the free-slip top boundary condition used in traditional numerical models, we apply a more realistic, stress-free surface boundary condition, which can avoid artifacts of the free-slip approximation. This is particularly important for thick, high viscosity lithosphere due to the absence of plate bending resistant forces and an effective no-slip boundary at the base of the lithosphere. We find that a smaller viscosity, thinner lithosphere generates higher and narrower topography than the larger viscosity, thicker case. A stratified lithosphere with a weak lower crust (a decoupling layer) also creates higher topography than the case of a homogeneous lithosphere, which can be understood by the lowered averaged viscosity. We then explore the role of elasticity and edge-driven topography using viscoelastic rheology and examine the differences in lithospheric deformation, stress level and distribution. We find that viscoelastic rheology can increase the uplift rates on Maxwell timescales due to the additional elastic component compared to purely viscous rheology. We also find that mantle driven uplifted topography creates extensional stress in the lithosphere while tectonic edge-driven uplift generates much lower compressional stress. Such signatures may be helpful to detect the dominant contribution to regional topography by jointly examining geodetic, geological, and seismic data.Earth and Planetary Science
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