Rock Microstructures
Period: first semester
Course Unit Contents:
The course will focus both on the formation of anisotropies within magmatic and metamorphic rocks,
so that distinguishing between deformations at melt present conditions versus subsolidus conditions will be clear.
A major concern within metamorphic rocks is the interrelationship between deformation and
mineral growth. Recognition of the relative timing between deformation and the evolution of metamorphic
mineral assemblage can give key information for the reconstruction of “Presssure - Temperature - Deformation”
(PTD) paths. We will dedicate part of the time to this important aspect.
Microstructures tell us much on the reaction progress within the rocks, and preserve significant information
on whether these formed under extensional or constrictional regimes. We may also be able to decipher the
overprinting relationships between transient deformation regimes.
Studying and understanding microstructures within rocks implies application of modern analytical techniques.
In this course, besides transferring to the students the necessary theoretical background of microstructural
analysis, we will apply Scanning Electon Microscope (SEM) - based analytical tools as Backscatter Electron
(BSE) imaging together with (Energy Dispersive Spectroscopy) EDS and Electron Back Scatter Diffraction (EBSD)
analysis to thoroughly understand nucleation, growth and deformation microstructures of minerals within
magmatic and metamorphic rocks. This will be anticipated by observation and discussion of microstructures
within HR-digitalized thin sections in plane and polarized light.
• Rhological transition within melt bearing systems.
•Factors controlling melt rheology and development of magmatic foliations.
•Rheological critical melt percentage (RCMP) or when melt bearing systems deform like solids.
•Foliation development in the solid state: schistosities, S-C fabrics, crenulation cleavages,
slaty cleavages.
•Analysis of inclusion trails within porphyroblasts.
•The concepts of pre-kinematic, syn-kinematic and post-kinematic porphyroblast growth.
• Overprinting relationships between metamorphic planar anisotropies.
•Preservation of high pressure mineral phases within garnet: implications on the
reconstruction of PTt-path within metamorphic rocks.
•Corona microstructures and their evidence for decompression during exhumation.
•Compositional growth-zoning versus diffusion modified chemical profiles in
metamorphic minerals.
•Epitaxial growth of metamorphic mineral to overcome the energetic nucleation barrier.
Evidence from microstructural analysis using EBSD.
•Post-entrapment thermally-induced shape change of mineral inclusions within garnet.
The role of surface energy control at high temperature metamorphism and the resulting
implications on the relative timing of mineral inclusions within porphyroblasts.
•Application of multiple novel SEM-FIB based analytical tools:
Microtomography, STEM, EDS chemical mapping, EBSD analysis.
Planned learning activities and teaching methods: Teaching is based on frontal lectures, SEM-based laboratory work aimed to unveil the significance of particularly diagnostic rock microstructures in terms of formation mechanisms and involved controlling processes, discussion in work groups of the potential interpretation of such rock microstructures.