Interpretation of the Seismic Structure beneath East Asia using Mantle Convection Model with Tectonic Plates

Abstract:

East Asia has been influenced by two convergent subduction systems since 200Ma: the Pacific domain and the Tethyan domain. The fast convergent and subduction process has had a significant influence on the evolution of mantle flow beneath this area.Great progress has been achieved in seismic tomography in the past decades and the seismic models significantly increased our knowledge of the mantle structure of East Asia. The dominant mantle structures are the stagnant fast anomalies laid at the 670km interface and the fast anomalies above the CMB. These anomalies are usually interpreted as subducted slabs, however, they are not well understood from a dynamical perspective and their evolution remains enigmatic.

In this study, we use a three-dimensional spherical mantle convection model with plate motion history for the past 200 Myrs to model the evolution of mantle structure beneath East Asia. We use a tracer method to mark the Izanagi, Tethys, Pacific, Indian plate at every run step and continuously trace their evolution.

The preliminary results show that the subducted Iaznagi and Pacific plates play an important role in the mantle evolution of East Asia. These plates first laid at the 670km discontinuity interface and spread out westwards after entering the mantle and then dropped into the lower mantle.After the complete subduction of the Izanagi plate at ca.55Ma, some of the plate remanents are trapped at the western edge of the stagnant Pacific slabs.The models predict that the subducted Izanagi plate is located beneath East Asia nowadays with its western edge at ~90°E, in a latitude range from 0~65°N and a depth range from 1400 to 2800 km.