An approach to 3D rock fabric analysis of ophiolitic rocks via X-ray micro-computed tomography.

Giamas, V.; Koutsovitis, P.; Sideridis, A.; Turberg, P.; Grammatikopoulos, T.; Petrounias, P.; Giannakopoulou, P.; Koukouzas, N.; Hatzipanagiotou, K.

X-ray micro-computed tomography (μCT) was initially applied for medical purposes only, however during the past two decades, this technique presents an exponential character in several studies including archeology, material sciences, engineering as well as in geosciences. The reason for this is its ability to visualize in a non-destructive manner to investigate the internal features of any sample considered (i.e., the mineral constituents of a rock sample). In this concise presentation, we will only focus on the chapter of 3D rock fabric analysis from the recently published article of Giamas et al. (2022), although their work primary investigates the effectiveness of μCT upon six geochemically different (mafic and ultramafic) ophiolitic rocks. The examined lithotypes consist of a gabbronorite and a hornblende gabbro for the mafic as well as a wehrlite, a harzburgite, a dunite and a chromitite for the ultramafic group. It should be noticed that several criteria have been taken into consideration (representative lithotypes, alteration/metasomatism, restricted number of participating minerals, primary mineral constituents with different densities and attenuation coefficient properties, variability in grain size distribution from a set of samples, textural homogeneous features within each sample). Apart from the mineral volumetric portions calculated through μCT, which were compared with other state-of-the-art-techniques (optical microscopy, mineral chemistry microanalyses-MINSQ, XRD, and QEMSCAN), fabric analysis can provide 3D information of mineral constituents regarding their textural and structural properties. Blob3D software (Ketcham, 2005) was used for mineral segmentation, separation, and mineral's volume - shape measurements that were further processed with the open-source TomoFab MATLAB code (Petri et al., 2020) for defining the individual best-fit ellipsoid that were used for the calculation of the fabric parameters (shape parameter T and anisotropy P'). The research outcomes can be considered of major importance in terms of resolving complex petrogenetic phenomena (mantle state, magma crystallization, deformation and/or alteration processes, identification of water-bearing phases, geodynamic implications), as well as for identifying deformation fabrics that can be critical for applied research purposes (usage as aggregates or as potential storage sites for CO2 mineralization).

OPHIOLITES; X-ray microscopy; COMPUTED tomography; METASOMATISM; GRAIN size

Bulletin of the Geological Society of Greece, 2022, p702

0438-9557

Academic Journal