The Earth is a Living Planet by Post Doc Ting Yang

The Earth is a living planet, as revealed by tectonic processes spanning various time and spatial scales, including earthquake, volcano eruptions, mountain building, basin formation, etc. All these tectonic processes are dominated by the solidus buoyancy flow inside the Earth's mantle - mantle convection.

Southeast Asia is a unique place to investigate the effects of mantle convection on surface tectonics. This intriguing place has the most prominent low dynamic topography on Earth at present, as indicated by numerical models and observations.

Sundaland, the continental core of Southeast Asia, underwent intense deformation in the past, as revealed by the low seismic velocity in the lithosphere and upper mantle, widespread rifting basins and high heat flux. However, Sundaland is tectonically quiet at present and manifests as the low seismicity and strain rate. We investigate global mantle viscosity and temperature structures with the constraints of geoid, free air gravity, gravity gradients and residual topography.

With the knowledge of mantle temperature and viscosity structures, we focus on the dynamic evolution of Southeast Asia, with dynamic models considering both lithospheric scale deformation and mantle convection. We demonstrate that a large mass of dense, cold slab material lay horizontally within the transition zone beneath southern Sundaland before the Miocene, due to the impedance of the 660 phase boundary. During the early Miocene the stagnant slab became unstable and penetrated into the lower mantle, forming a slab avalanche event. This slab avalanche event induced significant change in large scale topography, stress field and basin regimes and sedimentary environments in southern Sundaland.

We suggest that the slab avalanche might have occurred beneath other subduction zones and generated strong changes on surface tectonics.