COMPASS PhD Project 1: Combining plate tectonic movements and global flow models in a spherical geometry to study mantle flow, melting, and epeirogeny during rift initiation and basin growth
Supervisors: Prof J. Morgan, Dr M. Pérez-Gussinyé, Dr G. Eagles
This project aims to explore global mantle flow models and plate deformation on a spherical Earth. To this end we will explore the evolution of 3D mantle convection and plate deformation using numerical models constrained by plate velocities from plate kinematic reconstructions. This tool will allow researchers to simulate plate tectonic movements at the surface and simultaneously visualize the deeper deformation of lithosphere and mantle. The numerical model will be based on existing 3D viscous code in Cartesian coordinates that incorporates mantle melting. The main numerical task of the PhD project will be to translate this code into a 3D spherical mesh designed for the region in question, to incorporate plate velocities and the time-evolution of plate geometries as boundary conditions for mantle flow and a free-surface into the code to model vertical motions.
The numerical code will be used to study the history of basin opening by plate divergence in a region selected in conjunction with the industry partners. For illustration, we discuss the South Atlantic region. However, the North Atlantic/Arctic and Indian Ocean would be equally good areas to develop the methodology and workflow used in this project. In the South Atlantic, great controversy surrounds the roles of the Paraná plume in the opening, subsidence and salt accumulation histories of the Santos and Campos basins in South America and South Kwanza, Namibe and Benguele basins in Africa. Using a finer numerical mesh in the region, the model will be used to understand the interactions between plumes and opening rift systems. We will study these interactions by assuming different scenarios for the distribution of continental lithospheric thickness (e.g. distribution of thick cratons vs. thinner lithosphere), plume trajectories, and plate kinematics that affected these basins during rifting. We will allow these scenarios to evolve in the model in order to understand how plume material spreads under opening basins and influences their vertical motion and magmatism.
Specific deliverables of PhD project 1 with a projected timeline are:
o A numerical model that simulates in 3D the dynamics of extension of a particular region with velocity boundary conditions constrained by plate kinematics. (Years 1-3, initial model after year 1, comparison of different effects due to GPlates vs. Eagles BCs in years 2-3)
o Systematic study of the interaction between plate kinematics and plume activity and its relative role in the opening of new basins. (Years 2-3, initial results after year 2)
o Comparison between predicted subsidence/uplift patterns in regions that follow ‘amagmatic’ or ‘magmatic’ rifted margin evolution (initial results after year 2)
o Systematic study of subsidence/uplift history in 3D of an opening rift as a consequence of extension and plume activity. (final results after year 3)
o All source codes and scripts/files needed to recreate these worked examples will form part of the deliverables from each year of work.
We are looking for a computationally able student with a background in civil engineering, computing, physics, geophysics or a similar discipline. Aspects of plate tectonics and margin development necessary to undertake the work will be taught by the supervisors within the framework of the project.
COMPASS PhD Project 2: Influence of tectonic setting and extension velocity on basement and sedimentary architecture of rifted continental margins.
Supervisors: Dr Marta Pérez-Gussinyé, Prof Jason Phipps Morgan, Dr Graeme Eagles, Prof Peter Burgess
Extension of the continental lithosphere portrays a wide range of tectonic styles depending on factors such as initial lithospheric rheology and the velocity of extension. Understanding how and why these different tectonic styles developed is a key element for the prediction of petroleum systems at continental margins. In this project, we will pursue these experiments in a region of interest to consortia partners, with the South Atlantic chosen as an example to demonstrate the methodology and approach. The Central South Atlantic margins present an ideal natural laboratory to study the effects of rheology and rift speed on the styles of rifting and post-rift margin evolution. For example, from South to North along the South American margin, extension developed first on weak mobile lithosphere, in the Espírito Santo, Campos and Santos basins and then it initiated on cratonic one in the Camamu and Jacuipe basins. Understanding how these different rheologies acted with variations to extension velocity is a very important element in predicting the petroleum systems that are subject of ongoing exploration along these continental margins. This PhD project will use and develop 2D thermo-dynamic numerical models to investigate how the rheology and extension velocity influence the tectonic style, subsidence, heat flow history and hence petroleum system during rifted continental margin evolution. These models will incorporate a visco-elastic- ‘plastic’ rheology that can encompass flexural and fault-like modes of deformation in addition to ductile viscous flow. Model setups will also be constrained by seismic data, where available. Extension velocities and basin configurations in the numerical experiments will be constrained by the predicted time-histories of velocities and geometries that evolve in 2-D cross-sections through the larger-scale 3-D numerical models developed in Project 1. Numerical experiments will incorporate the syn‐ and post-rift sedimentary cover to analyze the impact of both extensional styles on sediment architectures and sediment deposition on extensional style during the whole margin history. Different algorithms will be explored to implement sedimentation, including linear and non-linear diffusion. Likewise, the thermal effects of sediment blanketing will be included, to test sedimentation effects on lower crustal rheology. Work will include the post-rift phase where the influences of evolving onshore-offshore topography will be analysed. All source codes and scripts/files needed to recreate these worked examples will form part of the deliverables from each year of work.
Specific deliverables of PhD project 2 are:
o Geodynamic simulations of lithospheric deformation, vertical margin motion, and sedimentation during rift, break-up, and drift stage of selected conjugate margins, including both ‘magmatic’ and ‘amagmatic’ rifting scenarios. (Year 1 — models with ‘ad- hoc’ BCs, Years 2-3 — BCs downscaled from 3-D regional models in PhD Project 1.)
o Classification of lithospheric deformation styles according to extension velocities, initial crustal architecture and rheology (Years 1-3), and sedimentation history (Years 2-3).
o Study of parameters and processes controlling the links between onshore and offshore sedimentation and erosion during the syn- and post-rift phase and their influence on onshore topographic evolution. (Year 3)