There and back - how well do rocks record their journey deep into the Earth?
The aim of this project is to determine the pressure evolution recorded by granitic rocks in the western Gneiss Complex in Norway.
During subduction, high-pressure metamorphic assemblages such as those found in eclogites and blueschists are formed in mafic rocks and are interpreted to record the behaviour of the subduction system. However, felsic rocks that are intercalated with subducted mafic rocks commonly lack metamorphic assemblages indicative of subduction.
Why this is case is still a mystery, but it poses the question of whether rocks can experience remarkable processes such as deep subduction and be apparently unaffected.
The Western Gneiss Complex in western Norway is arguably the most famous example of subduction of continental material to depths of more than 200km in some areas. The mechanisms that drove the return of the material to the surface are still debated. However one potential mechanism is that buoyant granitic crust was dragged into the mantle by the pull of the oceanic slab.
When the slab broke, the buoyant material bounded. Essential for this mechanism is that the granitic crust did not get converted to dense high-pressure mineral assemblages, despite the mafic rocks within the granites containing spectacular high-pressure eclogite mineral assemblages.
- The granitic rocks did not undergo conversion to dense high-pressure mineral assemblages, and therefore remained buoyant.
- The granitic rocks did convert to dense high-pressure mineral assemblage but were retrogressed as they returned toward the surface by mechanisms not requiring buoyancy.
The project aim will be achieved using the mineral assemblage software THERMOCALC, coupled with petrology and electron microprobe mineral compositional data. Laser ablation ICPMS analyses will be used to determine the timing of mineral growth in both rock packages as well as the fractionation of trace elements during metamorphism between age determining minerals and their associated metamorphic assemblages.
The project will involve fieldwork in Norway, undertaken collaboratively with researchers from Curtin University and the University of California. You will be required to make a contribution of $1000 to cover travel to Norway.
- Strong competence in Igneous & Metamorphic Geology III
- An interest in tectonic processes