Overview

Project Highlights:

  • Explore the fundamental process of subduction initiation;
  • Will use a multidisciplinary innovate method combining palaeomagnetism, structural geology, and geochronology;
  • Strong field component requiring sampling in Oman;

 

Overview:

Subduction is a key step in the solid Earth cycle that allows tectonic plates to move. During the formation of a new subduction zone, when lithosphere initiates its descent into the upper mantle, a number of tectonic, geochemical, and petrological processes affect the leading edge of the plate above the subduction zone (i.e., forearc). These transformations may provide fundamental insights into the still poorly understood process of subduction initiation.

Fluids released by the subducting plate during subduction initiation hydrate the overlying mantle and create a new mineralogical phase called serpentine. This process, known as “serpentinisation”, drastically reduces the strength of the mantle and enormously increases its magnetisation. The study of the magnetic and physical properties of serpentinised mantle rocks are therefore instrumental to track the location, entity, and timing of mantle hydration and hence of subduction initiation. A recently developed technique to date magnetite grains[1] may be used to constrain the timing of serpentinisation associated to subduction initiation. Subduction initiation also induces tectonic stretching in the forearc region. Extension may eventually result in new magmatism which is responsible for the formation of new oceanic lithosphere called “ophiolite”. Recent studies of ophiolites[2,3] have shown that the initial stages of subduction are frequently characterized by a pervasive stretching of the forearc, which produces lithosphere thinning and tectonic rotations. Reconstructing the kinematics of forearc deformation is key to constrain the style and mechanisms of subduction initiation.

The Oman ophiolite represents the ideal natural laboratory to study the chemical, petrological and tectonic processes associated to subduction initiation. It is the most complete and best-preserved ophiolite and is composed of a 5-7 km thick mantle sequence and a 4-5 km thick crustal sequence. This ophiolite formed in the forearc of a new subduction zone initiated in the Late Cretaceous at 104 Ma[4]. The goal of this project is to investigate the Oman ophiolite using a multidisciplinary approach, which employs palaeomagnetism, rock magnetism, magnetic fabric, geochronology, and petrology, to unravel the complex history of events associated to a past subduction initiation event.

Figure 1: Mechanism of subduction initiation based on the reactivation of extensional oceanic detachment faults along mid-ocean ridges, after Maffione et al. (2015). Note in the last stage the formation of an ophiolite (orange).

Methodology

Palaeomagnetism will be used to reconstruct the tectonic rotations potentially associated with regional forearc stretching. Magnetic fabric analysis (AMS) will be used to constrain the kinematics of deformation in the absence of major tectonic rotations (i.e., stretching directions). Rock magnetic analysis will be employed to identify the magnetic mineralogy resulted from the serpentinisation process. Petrological analysis using scanning electron microscope (SEM) observations will aid definition of the number of serpentinisation events by analysing the different families of serpentine veins. Geochronology on magnetite will finally put the subduction initiation process into a precise time frame.

Training and Skills

The main supervisor (Maffione) will provide training for the various techniques used in the palaeomagnetic laboratory, as well as for the structural geological analysis in the field. Additional training in advanced tectonic reconstructions using tools like GPlates will also be provided.

Timeline

Year 1: Literature reading; First field sampling campaign and structural geological analysis in Oman (2-3 weeks); Preliminary rock magnetic analyses at the PUMA lab.

Year 2: Second field work in Oman (2-3 weeks); Rock magnetic analyses at the PUMA lab; Data interpretation.

Year 3: Geochronological analyses and data interpretation; Interpretation of the data acquired so far and developing of a tectonic model; thesis writing; paper writing.

Partners and collaboration (including CASE)

No partners are involved in this training except for the supervisors.

 

Further Details

For further info please contact Dr Maffione at m.maffione@bham.ac.uk

For more info on the scientific activity of the PI Maffione go to www.marcomaffione.com

For further info on where and how to apply go to the CENTA website (http://www.centa.org.uk/training/)