Facitilites

Tools and Methods

Mineral reactions and phase transformations are responsible for first order changes in physical properties of solids such as chemical composition, density, seismic velocities and strength. The aim of a petrologist is to develop forward or inverse modelling tools to explain and quantify the direct observations of such transitions in natural samples.

All approaches are used to understand and evaluate:

• The interplay between mechanics and chemical processes.
• The duration of main metamorphic events.
• The influence of non-lithostatic pressure on metamorphic reactions.
• The dehydration and melting in deforming porous rocks.

The key methods/tools are:

Analytical methods

Our research involves application of high-end analytical and spectroscopic techniques with a focus on high spatial resolution to characterize the state of strain and the residual pressure.

Conventional petrology methods include Electron Microprobe Analyses (EMPA), Field-Emission-Gun Electron Microprobe Analyser (FEG-EMPA) for major and minor element compositions and Scanning Electron Microscope (SEM), Field Emission Gun Scanning Electron Microscope (FEG-SEM) and Crystal orientation mapping using electron backscatter diffraction (EBSD) for the study of surfaces and micro-crystallography on crystalline matter. Raman spectroscopy is used for barometric purposes and to quantify the water content in nominally anhydrous minerals (such as olivine).

 

EBSD map of a plagioclase rim

 

Material science cutting edge analytical techniques include a Focused-ion-beam sample preparation technique (FIB-SEM) which allows to reveal the three-dimensional size, shape, and distribution of microstructural features, i.e. the inclusion/host interface. Material is progressively cut into thin slices and series of parallel cross-sections and corresponding structural, chemical and crystallographic 2D information can be obtained. These data can be reconstructed into a 3D volume for visualization purpose and further analysis. The thin foils cut by FIB will be then analysed on Transmission Electron Microscope (TEM) in order to get a detailed description of inclusion/host interfaces (coherency and width) and element compositions in the immediate vicinity of the inclusion down to the nanometrescale.

 

Image of a FIB foil

 

Phase Equilibria Modelling

Phase equilibria modelling is commonly used to obtain P-T constraints along a geodynamic path which rocks in the Earth’s Litospehere experienced. In addition, phase equilibria modelling helps to describe and interpret chemical processes which led to a development of observed rock microstructures via P-T-X or X-X phase diagram sections or phase fractionation calculations. In our research, we use state-of-the-art software (e.g. Perplex, Thermocalc, Domino) that performs such phase equilibria calculations. Moreover, we develop our own thermodynamic tools for quantification of petrographic observations (see Research for details).

P-T section for a specific bulk rock composition

 

Numerical Modelling

Phase equilibria modelling provides important but incomplete constraints for the transient properties that occur in the earth’s interior. Such transient processes are thermal/chemical diffusion and deformation. We develop numerical codes (FEM/FDM) that are consistent with local equilibrium thermodynamics in order to investigate thermal, chemical and mechanical processes relevant to rocks in the Earth’s Lithosphere. We use GPU-accelerated simulations. All approaches are used to understand and evaluate:

Pressure variation in a polycrystalline rock under vertical shortening.