Formation of East Asian Stagnant Slabs Due To a Pressure‐Driven Cenozoic Mantle Wind Following Mesozoic Subduction

Abstract

The term "stagnant slab" usually refers to the widely distributed fast seismic anomalies within the circum-Pacific mantle transition zones (MTZ) (Fukao et al., 2009;Huang & Zhao, 2006). There are several proposed mechanisms for why slabs can stagnate in the MTZ. The first one is related to the buoyancy associated with phase transformations of major mantle minerals, where both the negative Clapeyron slope of the ringwoodite-bridgmanite transformation (Christensen & Yuen, 1985;Tackley et al., 1993) and the delayed pyroxene-garnet transformation (King et al., 2015) tend to trap the slab within the MTZ. The second one is about the viscosity structure (Gurnis & Hager, 1988), where either a large viscosity increase into the lower mantle or a thin low-viscosity-layer right below the 660 km is invoked (Mao & Zhong, 2018). The third one concerns the age of the subducting plates, where a progressively older subducting slab tends to result in obvious trench retreat and stagnant slabs in the MTZ (Yang et al., 2018). The fourth one is the trench retreat, commonly attributed as an important reason for slab stagnation (Christensen, 1996; van der Hilst & Seno, 1993;Zhong & Gurnis, 1995). Some recent studies suggest the potential role of former subduction (Hu & Gurnis, 2020;Liu et al., 2021), but the dynamic nature remains elusive. There is still no systematic evaluation of these effects using a data-driven thermal-chemical modeling framework.East Asia is an ideal location for studying subduction dynamics and slab stagnation. Numerous tomography models reveal high-velocity seismic anomalies in the MTZ beneath East Asia that are commonly interpreted as stagnant slabs (

Dynamics of the Subducted Izanagi-Pacific Plates Since the Mesozoic and Its Implications for the Formation of Big Mantle Wedge Beneath Eastern Asia

“…In this study, we perform global mantle convection models to examine the behaviors of the Izanagi plate and the Pacific plate since the Mesozoic time. We introduce a tracking procedure in numerical models to explicitly distinguish the slab materials of the two plates, which provides a more robust demonstration of slab dynamics in their evolutionary processes than identifying slabs solely from thermal structures as in many previous studies (e.g., Seton et al, 2015;Peng et al, 2021a;. Our results show a general match of present-day slab structures beneath Eastern Asia with those inferred from seismic tomography observations, especially in the upper-to-middle mantle depths.…”

“…Although some regional models have suggested that the weak layer has a small effect on slab stagnation (e.g., , global models have demonstrated that the weak layer is crucial to explain not only the stagnant slabs in the transition zone (e.g., East Asia) but also other slab structures (e.g., North America) that are observed in seismic tomography studies (Mao and Zhong, 2018). Recent numerical studies, on the other hand, have argued that a pressure-driven Cenozoic mantle wind is the dominant mechanism for the formation of the stagnant slabs beneath East Asia (Peng et al, 2021a). The linkage between the Izanagi plate subduction and the tectonic evolution of East Asia is still controversial because the slab dynamics of the Izanagi plate have not been well resolved.…”

“…In addition, global mantle convection models show that the stagnant slab under Eastern Asia largely results from subduction in the past 20-30 Myr (Mao and Zhong, 2018). The stagnation of the Izanagi-Pacific slab beneath Eastern Asia has been investigated in many numerical experiments (e.g., Seton et al, 2015;Peng et al, 2021a;. However, most of these studies have focused on the stagnation of the Pacific slab in the Cenozoic time, while whether the Izanagi slab in the Mesozoic time could be stagnant or not remains unclear.…”

Asthenospheric flow through the Izanagi-Pacific slab window and its influence on dynamic topography and intraplate volcanism in East Asia

“…Following the subduction of the Izanagi-Pacific ridge, however, hot material may then have flowed through the opened slab window into East Asia, and been driven further into this region by downwelling slabs during the Cenozoic. Indeed, this east-west Poiseuille flow following the subduction of the Izanagi-Pacific ridge has recently been noted, and invoked as a cause of the flat-slab subduction style of the Pacific plate (Peng et al, 2021).…”

A Lower Mantle Slab Below the East Asia Margin Constrained by Seismic Waveform Complexity

“…In contrast to the general northwestward subduction of the PSP, our imaged lower mantle slab presents a SE-dipping structure (Figure 10b), which suggests complicated mantle dynamics in the lower mantle. The recent global-scale dynamic models of Peng et al (2021) show examples with the lower-mantle portion of the subducted Pacific slab displaying an eastward-dipping direction from the shallower slab, due to a westward mantle flow going through the slab gap in between them. Alternatively, a slab avalanche into the lower mantle can produce a complicated slab morphology in the lower mantle with a possible reversed dipping direction (Agrusta et al, 2017;Goes et al, 2008Goes et al, , 2017Nakakuki et al, 2010;Yang et al, 2018).…”