Overview

Project Highlights:

  • New analytical technique to study fault connectivity
  • Use of industry software on unique academic 3D seismic dataset
  • Address fundamental question relevant to natural carbon capture via mineral carbonation

Thin crust at the feather edge of magma-poor margins is commonly underlain by mantle characterised by a velocity well below 8 km/s and a strong vertical velocity gradient up to normal mantle velocities (see Figure).  This anomalous mantle is generally accepted to result from its hydration and serpentinization.  However, it is not clear exactly how the water reaches the mantle to cause serpentinization.  The volume of water required implies that it comes from the overlying ocean, which implies that it passed through fractured brittle crust.  Observations that reduced mantle velocities occur where the crust was entirely brittle during rifting, and that the degree of serpentinization correlates with extension of the overlying crust, both support the idea that a fracture network within the crust is a critical element in magma-poor margin evolution (Perez-Gussinye & Reston, 2001; Bayrakci et al., 2016).

This project will investigate the nature of the crustal fracturing.  It is likely that seawater reached the mantle through a connected network of fractures through both crustal basement and the early syn-rift sediments that make up the tilted fault blocks.  The project will determine the connectivity of faults within the block at both seismic and a sub-seismic scales.  It will then investigate the role of the fault network in transporting seawater to depth by considering how the network responds to the evolving stress regime.  Implications for the transport of water through fractured mantle massifs exposed at slow and ultraslow spreading ridges will also be considered.  These mantle massifs are possible places where serpentinization and mineral carbonation resulting from the uptake of water might be stimulated to capture carbon (Kelemen and Matter, 2008).

Reduced mantle velocity (green colours) below fault blocks, Galicia margin (Bayrakci et al., 2016)

Methodology

The project will build on current work interpreting the 3D seismic volume, by interpreting the intrablock faults in terms of their connectivity, orientation, and dimensions, using the technique of network analysis. The connectivity will then be compared with the seismic properties of the underlying mantle.  A second aspect of the work will be to then consider the effect on the intra-block fault networks of stress before, during, and after slip on the block-bounding faults.  Of particular interest will be the changing dilatancy of these faults, providing constraints on the efficiency of the faults as conduits for fluid flow.

Training and Skills

CENTA students attend 45 days of general training throughout their PhD, including a 10 day placement.  In the first year, students will be trained as a single cohort in environmental science, research methods and core skills.  During the PhD, training will progress from core skills sets to master classes more specific to the student's projects and themes.  Training in the use of seismic interpretation software will be provided.  It is anticipated that the student will have the opportunity to participate in fieldwork on related projects involving mid-ocean ridge processes and continental extensional tectonics.  The project will benefit from a major collaboration involving Reston that collected 3D seismic data over the Galicia rifted margin.

Timeline

Year 1:  Seismic interpretation training.  Background reading.  Picking and characterisation of intra-block faults. 

Year 2:  Finalise interpretation of project dataset.  Network analysis of the faults to build a 3D model of their conenctivity modelling of transition zone observations.  Conference presentations. 

Year 3:  Finalise modelling of observations.  Develop consistent framework to describe non-volcanic passive margin evolution worldwide.  Conference presentations.  Write papers and PhD dissertation.

Partners and collaboration (including CASE)

The student will work within a large group of scientists at Birmingham, Southampton and Rice (USA), who are studying the Galicia rifted margin using a large 3D dataset the group collected in 2013.  However, only this project will be using the network analysis approach.  The project will also benefit from the application of network analysis in ongoing studies of igneous sill intrusion at Birmingham. 

Further Details

Contact Prof Tim Reston (t.j.reston@bham.ac.uk) for project-specific information.  See CENTA web page for information on how to apply and general information (http://www.centa.org.uk)