The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau
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Post-subduction tectonics can involve a wide range of spatiotemporal processes associated with regional and large-scale upper mantle forces. To better understand the interaction between these forces in collisional settings, we focus on active mantle dynamics beneath the East Anatolian Plateau, a well-documented segment of the Arabian-Eurasian continental collision zone. In detail, we use state-of-the-art instantaneous thermomechanical models by combining the advantages of 3D numerical modeling with high-resolution imaging techniques. We analyze the model’s outputs, such as 3D stress-strain and temperature variations of upper mantle convection and reconcile them with numerous geological and geophysical observations. Our results show prominent northward-directed channel flow in the mantle that cuts across the plateau and surroundings, from the Arabian foreland to the Greater Caucasus domain. This result reproduces and elucidates the proposed ~SW-NE-oriented Anatolian Background Splitting pattern and recent seismic low-ultra low-velocity anomalies. We argue that this large-scale upper mantle flow constitutes the engine for the long-wavelength dynamic topography (~400 m) in the region and promotes the relatively small-scale convection pattern by supporting intraplate rift tectonics in the extensional Van Lake zone.Eclogitization
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[1] The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (vS⊥) at the surface into its subducting plate motion component (vSP⊥) and trench migration component (vT⊥). Geodynamic models of progressive subduction demonstrate such dependence with five distinct slab geometries and corresponding partitioning ratios (vSP⊥/vS⊥): slab draping (vSP⊥/vS⊥ ≤ 0.5), slab draping with recumbent folds (0.5 < vSP⊥/vS⊥ < ∼0.8), slab piling (∼0.8 ≤ vSP⊥/vS⊥ ≤ ∼1.2), slab roll-over with recumbent folds (∼1.2 < vSP⊥/vS⊥ < ∼1.5) and slab roll-over (vSP⊥/vS⊥ ≥ ∼1.5). The model findings have been applied to subduction zones in nature with well-resolved slab geometries, for which subduction partitioning ratios have been calculated during the last 20 million years in two global reference frames: the Indo-Atlantic and Pacific hotspot reference frames. The model-nature comparison determines in which reference frame subduction partitioning ratios are most in agreement with observed slab geometries. In the Indo-Atlantic frame, five (out of five) selected subduction zone segments with well-resolved slab geometries, plate velocities and trench velocities (Japan, Izu-Bonin, Mariana, Tonga, Kermadec) agree with the geodynamic model predictions, as calculated subduction partitioning ratios match the observed slab geometries. In the Pacific frame the partitioning ratio of only one subduction zone segment (Izu-Bonin) matches observations. It is thus concluded that the Indo-Atlantic hotspot reference frame is preferred over the Pacific one as a subduction zone reference frame in which to describe plate motions, subduction kinematics and mantle flow.
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The convergent subduction zones and the divergent spreading ridges are essential tectonic units that are widely distributed in the South China Sea and the surrounding regions, governing the regional tectonic evolution. Subduction-spreading interaction may be present between these two tectonic units, especially when they are located adjacent. Quantitative study of subduction-spreading interaction remains insufficient. Using 2D thermomechanical numeric modeling, we systematically study subduction-spreading interaction with particular attention paid on the influence of lower plate spreading versus upper plate spreading on subduction development. Our modeling results provide the following findings. (1) Intensive interaction is present between the adjacently located spreading center and subduction zone through plate motion and mantle convection, and positive feedback is present between these two units, i.e., spreading promotes subduction and vise verse. (2) The location of spreading center either on the upper or lower plate facilitates the formation of passive and active subduction, respectively, and the offset distance between the two units affects the intensity of subduction-spreading interaction. (3) Subduction-spreading interaction may be widely present in the South China Sea and the surrounding regions, where multiple subduction zones and spreading centers distribute adjacently in the present and evolved episodically in the past.
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This research is about the distribution of earthquake in subduction zone and calculation of subduction angle in the central Sumatera period 1967-2016. The data used in this research is earthquake data period January 1, 1967 until December 31, 2016 associated with the subduction zone. Research region consist of West Sumatera, Riau and North Sumatera. This region is made by following the slope of the subduction zone using GMT 5. Graphic of the relation between distance and depth every earthquake event is processed using polynomial method to be able to know the trend of subduction zone in this region. While, to find out the subduction angle in this region, calculation with the first derivative of the parabolic equation have been do. The results show that the subduction trend within 50 years is calculated in 10 years interval, the displacement that occurs is not too visible. But, it shows that the longer, the more subdued. While the angle of subduction at 50 km, 100 km, 150 km and 200 km respectively is 22.68°, 35.73°, 42.89° and 47.72°. This shows that the deeper, the larger subduction angle is formed.
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Subduction initiation is one of the main unclear aspect of plate tectonics. When studying subduction processes,
subduction initiation is therefore generally avoided as it constitutes a problem in itself. The easiest way to avoid this
problem in numerical models is to start the simulations with either a pre-existing subduction zone or a pre-existing
weak suture zone. In the Wilson cycle, as subduction initiation is often supposed to correspond to the first stage
when an oceanic lithosphere formed during extension turn in compression, we here present 2D thermo-mechanical
models of continental rifting followed by compression. While some of the models evolve toward subduction(s),
they often do not occur at the expected location. This poster aims to discuss the results obtained in such models
and the consequences of prescribing initial weak suture zones in the numerical models.
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Historic earthquake sequences on subduction zones that are similar to the Cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern United States. Based on systematic comparisons of several physical characteristics, including physiography and seismicity, subduction zones that are deemed most similar to the Cascadia subduction zone are those in southern Chile, southwestern Japan, and Colombia. These zones have all experienced very large earthquake sequences, and if the Cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length, then earthquakes of very large size (M_w > 8 1/2) must be considered. Circumstantial evidence is presented that suggests (but does not prove) that large subduction earthquakes along the Cascadia subduction zone may have an average repeat time of 400 to 500 yr.
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Subduction is the phenomenon of movement of one lithospheric plate under another, arising in connection with the heterogeneity of both geometrical and physical parameters of the lithospheric plates approaching each other. Such phenomena can occur in land, ocean and coastal areas. Active boundaries of the plates are divided into two types – subduction and collision ones. Collision processes are peculiar to the interaction of continental lithospheric plates and lead mainly to the twisting and generation of new mountains, while the subduction ones tend to cause earthquakes. By subduction, a part of the ocean floor sinks beneath the land plate. At great depth this part melts and due to the spreading it spreads and forms new crust both under the land and under the ocean. Subduction zones were discovered and described by the seismologist Benioff. Earthquakes occur most frequently in these zones. Benioff called them seismic focal zones, now they are called Benioff zones. There are attempts to explain the reasons for such properties of the Benioff zones, but they are not based on rigorous mechanical and mathematical approaches and are not convincing. The starting earthquakes are studied in the sone of subduction.
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Flat subduction can significantly influence the distribution of volcanism, stress state, and surface topography of the overriding plate. However, the mechanisms for inducing flat subduction remain controversial. Previous two-dimensional (2-D) numerical models and laboratory analogue models suggested that a buoyant impactor (aseismic ridge, oceanic plateau, or the like) may induce flat subduction. However, three-dimensional (3-D) systematic studies on the relationship between flat subduction and buoyant blocks are still lacking. Here, we use a 3-D numerical model to investigate the influence of the aseismic ridge, especially its width (which is difficult to consider in 2-D numerical models), on the formation of flat subduction. Our model results suggest that the aseismic ridge needs to be wide and thick enough to induce flat subduction, a condition that is difficult to satisfy on the Earth. We also find that the subduction of an aseismic ridge parallel to the trench or a double aseismic ridge normal to the trench has a similar effect on super-wide aseismic ridge subduction in terms of causing flat subduction, which can explain the flat subduction observed beneath regions such as Chile and Peru.
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