Eclogites and garnet peridotites occurring in Liverpool Land in the southern part of the East Greenland Caledonides are well known (Augland et al. 2010, 2011). However, the conditions of peak metamorphism have not been established due to the lack of phases well suited for geothermobarometry. Observations of garnet with quartz inclusions surrounded by radial fractures in thin section could indicate the presence of former coesite. Recent methodological advances in the use of electron backscatter diffraction (EBSD) for pseudomorph recognition allow the unambiguous identification of coesite from quartz that has transformed from coesite to quartz during retrogression from ultrahigh-pressure metamorphic conditions (Goddard et al. 2025). Furthermore, high‑resolution (HR) EBSD enables the quantification of residual stress in crystals such as garnet that have experienced rapid exhumation from extreme conditions, as have the eclogites of East Greenland.
This study aims to test whether potential pseudomorphs after coesite are present within garnet crystals in eclogites, and to determine how much residual stress is stored in garnets that were exposed to (ultra-)high-pressure (UHP) conditions and subsequently rapidly exhumed to upper crustal levels. Well-studied UHP eclogites from the Western Gneiss Region, Norway, will be used for comparison.
The thesis will test new scanning electron microscopy (SEM) methodology using the state-of-the-art high-resolution SEM at the Department of Geosciences. The outcome of this study will be significant in advancing and testing HR‑EBSD methods applied to (U)HP rocks and will have important implications for interpretations of the tectonic evolution of the East Greenland Caledonides, as well as for constraining collisional models for the Caledonian Orogeny.
References
- Augland, L. E., Andresen, A., & Corfu, F. (2010). Age, structural setting, and exhumation of the Liverpool Land eclogite terrane, East Greenland Caledonides. Lithosphere, 2(4), 267-286.
- Augland, L. E., Andresen, A., & Corfu, F. (2011). Terrane transfer during the Caledonian orogeny: Baltican affinities of the Liverpool Land eclogite terrane in East Greenland. Journal of the Geological Society, 168(1), 15-26.
- Goddard, R. M., Cross, A. J., Lloyd, G. E., Breithaupt, T., Kumamoto, K. M., Dyck, B. V., ... & Bidgood, A. K. (2025). A microstructural signature of the coesite-quartz transformation: New insights from high-pressure experiments and EBSD. Earth and Planetary Science Letters, 672, 119622.