Late-Cretaceous Izanagi Flat Subduction below East Asia and Tectonic Responses

Abstract:

Major questions remain on the configuration of Mesozoic subduction and tectonic evolution along the western Pacific margin. We reproduced the possible subduction scenarios during this time based on multiple recent plate reconstructions. Although there are large differences in the Mesozoic location and migration of the western Pacific subduction zones (e.g. Seton et al., 2012, Müller et a., 2016, Müller et al., 2019, Torsvik et al., 2019), global data-assimilation models assimilating these inputs (surface velocities and sea-floor ages) since 200 Ma consistently predict that the Izanagi slab experienced a period of flat subduction during the Late Cretaceous. This subduction configuration is also important for reproducing the present-day slab structures.

More tests show that the former subduction history is the key reason for the flat-slab formation. With the model’s starting age being 200, 120, 100 and 80 Ma, respectively, the slab dipping angle during the Late Cretaceous increases progressively. The models starting from 200 and 120 Ma both formed a flat Izanagi slab, but the flat portion in the latter was much smaller than in the former. These results confirm the recent proposal that the subduction duration is a dominant control for the formation of flat slabs (Hu & Gurnis, 2020). Physically, former subducted slabs affect the morphology of the incoming slab through the generation of a landward mantle flow that lifts the new slab from underneath.

A flat Izanagi slab during the Late Cretaceous represents a previously unrecognized subduction scenario. This can potentially explain multiple aspects of the tectonic history of the region. For example, the flat slab thinned the continental lithosphere above it and locally thickened the lithosphere at the slab front that coincides with the present-day North-South Gravity Lineament, a location where prominent Late-Cretaceous exhumation was observed. The modeled lithosphere thickness is also consistent with the seismically observed lithosphere thickness in East Asia. Location and timing of this flat slab strongly correlate with the abrupt termination of Mesozoic intraplate volcanisms and tectonic inversion of major sedimentary basins in eastern China.