Preface: Pacific Plate Subduction and the Yanshanian Movement in Eastern China
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Abstract Plate tectonics requires the formation of plate boundaries. Particularly important is the enigmatic initiation of subduction: the sliding of one plate below the other, and the primary driver of plate tectonics. A continuous, in situ record of subduction initiation was recovered by the International Ocean Discovery Program Expedition 352, which drilled a segment of the fore-arc of the Izu-Bonin-Mariana subduction system, revealing a distinct magmatic progression with a rapid timescale (approximately 1 million years). Here, using numerical models, we demonstrate that these observations cannot be produced by previously proposed horizontal external forcing. Instead a geodynamic evolution that is dominated by internal, vertical forces produces both the temporal and spatial distribution of magmatic products, and progresses to self-sustained subduction. Such a primarily internally driven initiation event is necessarily whole-plate scale and the rock sequence generated (also found along the Tethyan margin) may be considered as a smoking gun for this type of event.
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Abstract Although plate tectonics is well established, how a new subduction zone initiates remains controversial. Based on plate reconstruction and recent ocean drilling within the Izu‐Bonin‐Mariana, we advance a new geodynamic model of subduction initiation (SI). We argue that the close juxtaposition of the nascent plate boundary with relic oceanic arcs is a key factor localizing initiation of this new subduction zone. The combination of thermal and compositional density contrasts between the overriding relic arc, and the adjacent old Pacific oceanic plate promoted spontaneous SI. We suggest that thermal rejuvenation of the overriding plate just before 50 Ma caused a reduction in overriding plate strength and an increase in the age contrast (hence buoyancy) between the two plates, leading to SI. The computational models map out a framework in which rejuvenated relic arcs are a favorable tectonic environment for promoting subduction initiation, while transform faults and passive margins are not.
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Geoscientists use plate tectonics to explain many aspects of both continental evolution and evolution of the planet as a whole. The subduction of material at convergent plate boundaries forms a fundamental component to the theory of plate tectonics. Plates, continents, subduction zones, and spreading centers all exhibit motion and geometric evolution, so to try and resolve the past geometries of the planet, geologists have utilized plate tectonic reconstructions. Here we present a three‐dimensional image of the subducted Indo‐Australian plate below southeast Asia and show that the geometry of the subducted slab at depth is intimately related to the geometric evolution of SE Asia over the past 50 Ma, including the collision of India with the Asian continent. We show how the once semicontinuous subducting Indo‐Australian plate has been segmented during collision between India, Australian, and the subduction margin to the north. Thus we have found that the geometry of the subducted plate should form a key component to the interpretation of the evolution of Earth's surface, as complexities and evolution of the subducted plate are manifest in the evolution of the overriding plate.
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Using depth-dependent layers and considering the subduction angle the Pacific plate to NE China,we build a vertical static 2D finite element model about the Pacific plate diving into NE China with subduction velocity of the Pacific plate.By altering subducting angle,we discuss numerically the possible subducting process and its effects on deep and shallow earthquake.The results of our models show the stress distribution of the whole research region including total characteristic feature and region characteristic,and the active faults and its adjacent areas response to the stress from deep region.Our research results imply that the subduction angle of the Pacific plate and the environment around faults in the crust having great effects on deep and shallow earthquake activities.
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The largest earthquakes occur at subduction zones, where one plate descends beneath another into the underlying mantle, at a convergent plate boundary. Some subduction zones seem to host more large earthquakes than others (Fig. 1), potentially reflecting the influence of large-scale geodynamic processes, which vary from one subduction zone to the next.
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Significance Subduction, the process by which tectonic plates sink into the mantle, is a fundamental tectonic process on Earth, yet the question of where and how new subduction zones form remains a matter of debate. In this study, we find that a divergent plate boundary, where two plates move apart, was forcefully and rapidly turned into a convergent boundary where one plate eventually began subducting. This finding is surprising because, although the plate material at a divergent boundary is weak, it is also buoyant and resists subduction. This study suggests that buoyant, but weak, plate material at a divergent boundary can be forced to converge until eventually older and denser plate material enters the nascent subduction zone, which then becomes self-sustaining.
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The seismicity, structure and tectonics of the Indian/Pacific plate boundary in the North Island of New Zealand have been studied by means of a microearthquake traverse oriented in the direction of dip of the subducted Pacific plate and extending for about 210 km. The geometry of the top of the Pacific plate is inferred from a band of concentrated microearthquake activity approximately 10 km thick which is identified with the crust of the plate. The Pacific plate has two knee-like bends, one where the top of the plate is about 25 km deep, the other below the volcanic front, where the plate is about 70 km deep. The shallower bend and subsequent restraightening of the plate are related to phase changes in the plate, the deeper bend to volcanism. Composite focal mechanisms indicate that seaward of the shallower bend the Pacific plate is being loaded by the Indian plate, whereas landward of this bend the Pacific plate is sinking under its own weight.
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