- This project will unravel the least understood and most intriguing processes of plate tectonics: subduction initiation
- This project will apply a recently developed geochronological method (Lu-Af) to date rocks formed during past subduction initiation events
- The project will require field work in the Balkan ophiolites (Serbia, Albania, Macedonia, and Greece) and lab work in several world-leading geochronological and palaeomagnetic laboratories.
Plate tectonics is the most unifying and revolutionary theory in Earth sciences. However, 50 years after its formulation fundamental questions about how plate tectonics works still remain unanswered. In particular, the formation of new subduction zones (whereby one tectonic plate starts to sink underneath another one) is poorly understood. Current models suggest that subduction can either initiate spontaneously due to gravitational instability, or be induced by external tectonic forces. In the last decade ophiolites (emerged relics of ancient oceanic lithosphere) have been crucial to study subduction initiation processes. Most ophiolites, in fact, form during subduction initiation above an incipient subduction zone. A recent work in the Oman ophiolite (Guilmette et al., 2018) used the time lag between the formation of the ophiolitic crust and the formation of the metamorphic layer found at its base to discriminate between forced and spontaneous subduction initiation. These metamorphic rocks, known as metamorphic sole, are key to constrain the age of subduction initiation as they form during the initial moment of subduction development. A substantial difference between the ages of ophiolitic crust and metamorphic sole would indicate a forced subduction initiation, while similar ages would suggest a spontaneous subduction initiation.
The primary aim of this project is to reconstruct the style (spontaneous vs. forced) of a past, major subduction initiation event to understand the possible mechanisms and causes behind the inception of a subduction zone. The ideal natural laboratory to study subduction initiation processes is an ophiolite belt running for hundreds of kilometers from the Alps in northern Italy to the Dinarides and Hellenides in the Balkan Peninsula. These ophiolites are relics of oceanic lithosphere formed during, and as a result of a major subduction initiation event occurred within the Neotethys Ocean during the Jurassic. Available geochronological ages from both the crust and metamorphic sole of the Balkan ophiolites are similar, suggesting a spontaneous subduction initiation. However, ages from the ophiolitic crust are sparse and those from the metamorphic sole used Ar39-Ar40 method, which does not date the actual metamorphism but rather the cooling occurring after it. Obtaining new ages from these ophiolites is key to better understand one of the major subduction initiation events of the Earth’s history.
Two to three sampling campaigns will be carried out in Serbia, Albania, Macedonia, and Greece. Standard U-Pb geochronology on zircons will be used to date the ophiolitic crust, while the age of the metamorphic sole underlying these ophiolites will be determined using the new Lu-Af dating method on garnet (Guilmette et al., 2018).
In addition to the geochronological analysis, palaeomagnetic analysis will also be carried out to reconstruct the initial orientation of the subduction zone (Maffione et al., 2017; Maffione and van Hinsbergen, 2018). Palaeomagnetic samples will be collected from the sheeted dyke section of these ophiolites, and the paleomagnetic directions will be computed using standard palaeomagnetic techniques. A net tectonic rotation analysis (Allerton and Vine, 1987) using the computed paleomagnetic directions will then be applied to reconstruct the geometry of the subduction zone and infer the potential geodynamic causes of subduction initiation.
Training and Skills
Training in both geochronology and palaeomagnetism will be provided by the main supervisor Maffione and co-supervisors. Also, training in ophiolite geology will be provide in the field by Dr Maffione. The student will acquire new knowledge in the use of Lu-Af and U-Pb dating techniques, as well as in palaeomagnetism, rock magnetism, and the application of net tectonic rotation analysis, which has a wide application in tectonic and structural geological studies.
Year 1: Literature review; one or two field sampling campaign in Serbia and Albania; paleomagnetic analysis of rocks from the Serbian and Albanian ophiolites; geochronological dating of these two ophiolites.
Year 2: One or two field sampling campaign in Macedonia and Greece; paleomagnetic analysis of rocks from the Macedonian and Greek ophiolites; geochronological dating of these two ophiolites.
Year 3: Continuation of the palaeomagnetic and geochronological analysis; paper and thesis writing.
Partners and collaboration (including CASE)
No partners are involved in this project.
For further info please contact Dr Marco Maffione at: firstname.lastname@example.org
For more info on the scientific activity of the main supervisor go to: www.marcomaffione.com
For further info on how to apply to this project go to the CENTA website: http://www.centa.org.uk