Environmental Sciences
In Environmental Sciences, we address global challenges by investigating a range of materials from the composition of airborne pollutants, to the microstructures of critical minerals and those of rocks for volcanic and earthquake hazard analysis. We identify sources of contamination, analyse the processes that control geohazards , and develop effective strategies for environmental protection and sustainability.
The mineralisation of boron-bearing dumortierite
This UK-India collaboration presents the first comprehensive EBSD study of the mineralisation mechanisms of dumortierite, a rare aluminous borosilicate mineral. The research focuses on vein mineralisation in metapelitic schists from Girola hill, Central India. Critical boron-bearing minerals like dumortierite are of high interest for their applications in renewable energy (wind turbine blades), borosilicate glass manufacturing, and health products. Electron microscopy enabled whole system characterisation using EBSD and revealed that dumortierite needles crystallises ystematically along muscovite cleavage surfaces. These advanced microstructural analyses demonstrated that the migration of hydrothermal fluids in the subsurface is facilitated by ripplocations, newly discovered crystal defects, which focus the crystallisation of dumortierite within mica-rich rocks.
Figure: (a) Backscatter electron image showing different mineral phases (Ky = kyanite, Ms = muscovite, Dum = dumortierite). (b) Inverse pole figure map obtained from EBSD showing the common orientation of dumortierite grains (blue). (c) Pole figures of dumortierite crystallographic axes a, b and c ([100], [010], [001]) shown as raw data (top) and contoured data (bottom). (d) Pole figures of muscovite crystallographic axes a ([100]) and poles to crystallographic planes (010) and (001), shown as raw data (top) and contoured data (bottom).
Deformed Eclogite Rheology
This study by Dave McNamara (et al) examines omphacite-rich eclogites sourced from the Zermatt-Saas unit in the Italian Alps to understand the rheological properties and flow of subducted oceanic crust. Electron microscopy identified the presence of sharp, asymmetrical chemical zonation and a lack of deformation microstructures within the grains. This proved that fluid-assisted diffusion creep is the primary mechanism responsible for the rock's lattice preferred orientation (LPO) and overall strength during exhumation. By integrating these microstructural observations with thermodynamic pseudosection modelling, the study demonstrated that diffusion creep can dominate eclogite deformation at high pressure-temperature conditions, challenging previous assumptions that dislocation creep is the sole driver.
Figure: a) Left: Crossed polarised photomicrograph of a clinozoisite grain that postdates eclogite foliation development from Sample S6.14 showing variable birefringence colours; Right: An Fe EDS map of the same grain showing concentric Fe zoning matching the birefringence patterns. b) Left: Crossed polarised photomicrograph of two foliated clinozoisite grains in Sample S6.14 showing asymmetrical changes in birefringence colours; Right: An Fe EDX map of the same two clinozoisite grains showing weak Fe zoning matching the birefringence pattern. Blue birefringence colours relate to decreased Fe3+ content while orange birefringence colours relate to increased Fe3+ content.
D. D. McNamara, J. Wheeler, M. Pearce, D. J. Prior (2024) Journal of Structural Geology https://doi.org/10.1016/j.jsg.2023.105033