Algorithms and applications of geodynamic modelling of rapid extension processes in SE Asia

The incompressible Boussinesq approximation have become a widely accepted and standardised strategy by the geodynamics community to solve the Stokes equations that describe the thermo-mechanical behaviour of Earth’s interior. It is usually reasonable to assume that rocks comprising the lithosphere and mantle are (nearly) incompressible if one is focused on studying processes occurring at the uppermost part of the Earth. However, this hypothesis does not hold if attempt to compute deep mantle calculations or volumetric phase changes at lithospheric depths such as serpentinisation or melt extraction. In this thesis, I focus on the mathematical description, numerical implementation and benchmark of a fully compressible formulation of the Stokes equations so that volumetric strain can be accounted for, when necessary. Furthermore, volumetric increase rising from brittle failure is nearly always neglected. Subsequently, I have developed a visco-elasto-plastic constitutive law using an associated Drucker-Prager flow low for geodynamical processes. Finally, I combined this tool with geochronological and geothermobarometric data to investigate the exhumation of metamorphic core complexes in Indonesia. South East Asia covers roughly the 15% of the Earth’s surface and represents one of the most tectonically active regions in our planet, yet its tectonic evolution remains relatively poorly studied and understood in comparison with other heavily studied regions of the Earth. Recent episodes of extension in SE Asia have been associated with subduction initiation, sedimentary basin growth and phases of crustal melting, uplift and extremely rapid exhumation of young (< 5 Ma) metamorphic core complexes. In this Ph.D. I applied numerical tools to better comprehend some of these recent events that occurred (and many of them still ongoing) in SE Asia. Therefore, numerical models are used to better constrain the thermal conditions of the lithosphere and extension rates at which core complexes might have developed and rapidly exhumed in SE Asia. In particular, I compare available geothermobarometric data obtained from samples of the Palu Metamorphic Complex (PMC) with synthetic p-T paths computed from the numerical models.