Evolution of mantle structure beneath the northwest Pacific: Evidence from seismic tomography and paleogeographic reconstructions

Abstract

Plate motions and subducting slab morphology are intricately connected, and through the integration of seismicity, tomographic images, and relative plate motions, the evolution of mantle structure can be interpreted. Tomographic images of P wave, shear wave speed, and bulk sound speed perturbations of the northwest Pacific region have been interpreted to define the extent and geometry of the subducting Pacific plate. We have found that the subducted Pacific plate beneath the Japan and Kurile arcs is coherent but is very complex at the junction of the two arcs near the Hokkaido corner, as the slab subduction angle decreases from north to south while the slab thickens. The Pacific slab beneath the Japan arc is slightly thinner and subducting through the upper mantle at a less steep angle than the slab beneath the Kurile arc. As the slab reaches the 660‐km discontinuity it becomes stagnant and lies in a horizontal position on top of the transition zone both beneath the Izu and Japan arcs. In contrast, the slab beneath the Kurile arc is subducting at a steeper angle and penetrates through the transition zone into the lower mantle. The difference in slab morphology appears to be due to a combination of change in dip of the subducting plate and the convergence velocity of the Pacific plate along the margin. A new paleogeographic reconstruction of northeast Asia was assembled to evaluate the plate motions that could explain the foundation of the current slab morphology. The plate reconstruction was based on Euler pole motions of the Pacific, Philippine, Amurian, Okhotsk, and North American plates relative to stable Eurasia plate. The new tectonic model illustrates the collision of the Japan and Kurile arcs, the opening of the Kurile Basin, disparity in Pacific plate velocities along the arc, and different rates of trench retreat along the Izu, Japan, and Kurile segments of the western Pacific margin. The plate motion model was interpreted in conjunction with the physical properties of the mantle imaged with the P wave and joint tomography to assess the evolution of the Pacific plate morphology since the mid‐Miocene and to provide constraints on the plausible plate motions in the region.

The influence of plate boundary motion on planform in viscously stratified mantle convection models

“…In contrast, we find converging plate boundaries have a significant effect on the lower mantle convective planform, even with the largest upper mantle/lower mantle viscosity contrasts considered. If we adopt the conventional view that fast seismic velocity anomalies represent cold, downwelling convection limbs, this is consistent with the observation that fast seismic velocity anomalies that reach the surface at trenches can be readily identified in seismic tomograms extending into the transition zone and beyond [e.g., van der Hilst et al , 1997; Miller and Kennett , 2006] and fast anomalies in the lower mantle that can be linked to the location of subduction zones in the past [e.g., Van der Voo et al , 1999].…”

Small scale hot upwelling near the North Yellow Sea of eastern China

“…Some tomographic studies show the stagnant subducting slabs above the 660 [ Fukao et al , 2001; Huang and Zhao , 2006], while other tomographic studies show part of the subducting slab reaching a depth of 800 km or more [ Bijwaard et al , 1998] beneath Eastern China. However, the slab's age and rigidity may influence the tomographic images and their interpretations [ Miller and Kennett , 2006].…”

Topography of the 410 and 660 km discontinuities beneath the Korean Peninsula and southwestern Japan using teleseismic receiver functions

“…This indicates that differences in depth of the 660 might be related to the characteristics of the slabs subducting at the Japan Trench and the Izu-Bonin Trench. The Japan slab subducts with an inclination of 30° [Miller and Kennett, 2006] and a convergence rate of 9.2 cm/yr [DeMets et al, 1994], and the Izu-Bonin slab subducts with an inclination of 45° [Miller and Kennett, 2006] and a convergence rate of about 6 cm/yr [Seno et al, 1993]. This difference in the angle of subduction of these two slabs in the northwestern Pacific, which has been attributed to the complex trench rollback history [Miller and Kennett, 2006], has also been identified by the tomographic models ( Figure 2).…”

“…The Japan slab subducts with an inclination of 30° [Miller and Kennett, 2006] and a convergence rate of 9.2 cm/yr [DeMets et al, 1994], and the Izu-Bonin slab subducts with an inclination of 45° [Miller and Kennett, 2006] and a convergence rate of about 6 cm/yr [Seno et al, 1993]. This difference in the angle of subduction of these two slabs in the northwestern Pacific, which has been attributed to the complex trench rollback history [Miller and Kennett, 2006], has also been identified by the tomographic models ( Figure 2). The geometrical properties of subducting slabs descending into the MTZ are determined by Journal of Geophysical Research: Solid Earth 10.1002/2014JB011149 their angles of subduction and their convergence rates.…”