Nanoscale structures and properties of carbonate faultspan> mirrors revealed by scanning electron and scanning transmission electron microscope images, electron energy loss and Raman spectra

This data publication contains scanning electron microscope (SEM) and (scanning) transmission electron microscope ((S)TEM) images as well as electron energy loss spectra (EELS) and Raman spectra of the principal slip surface of carbonate faultspan> mirrors. We analysed a total of eleven samples to investigate the formation mechanisms of fault mirrors in carbonates. The samples were taken as drill cores in Central Greece from two different outcrop locations. The first location, close to Arkitsa, is a large anthropogenic outcrop exposing three large fault planes. The second location is close to Schinos and was also formed by human interaction at the side of a gravel road. The data set contains supplemental material to the publication "Mechanisms of fault mirror formation and fault healing in carbonate rocks" by Ohl et al., (2020). In addition to the electron microscopy images we provide the spectra files of the Raman and EELS measurements for the identification of the carbon species in relation to the principal slip surface. The publication concludes that decarbonation of calcite during fault slip and the subsequent reaction of the decarbonation products produces fault mirror surfaces. Post-seismic hybridization of carbon results in partly-hybridised amorphous carbon and contributes to connecting hanging wall and footwall. In addition, post-seismic carbonation of portlandite produces secondary nano-sized calcite crystals < 50 nm facilitating fault healing.

The SEM images were acquired on an FEI Helios Nanolab G3 DualBeam focused ion beam scanning electron microscope (FIB-SEM). For the preparation of TEM foils, prior to ion-beam deposition of platinum, a 200-nm layer of platinum was deposited by electron-beam precipitation. TEM imaging was carried out with an FEI Talos F200X at 200 kV acceleration voltage and 5 – 10 nA beam current. Electron imaging was done at the Utrecht University electron microscope center, The Netherlands. EELS data was acquired using a Zeiss Libra 200FE at 200kV with an in-column Omega energy filter at the Westfälische Wilhelms-Universität (WWU) in Münster. The energy resolution of the EELS analyses was 0.7 eV, measured at the full width at half maximum (FWHM) of the zero-loss peak. Energy loss spectra were obtained at 250,000× magnification with a 100 μm filter-entrance aperture giving an effective aperture of about 40 nm on the sample. Raman spectroscopy was carried out using a WiTec ALPHA300R confocal microscope and a 532-nm wavelength laser and a spectrometer grating of 600 grooves/cm.

This data publication consists of SEM and (S)TEM images organized in folders named Figure X, where X is the number of the supplemental figure referred to in Ohl et al. (2020). The contents of these folders are described in the 2020-007_Ohl-2020-List_of_files.xls. In addition, the untreated Raman spectroscopy and electron energy loss spectroscopy spectra are provided as tab-separated files containing the XY coordinates for Arkitsa and Schinos. For the Raman spectroscopy measurements, the first column is the wavenumber shift in [rel. cm-1] and the second column refers to counts per second [cts/s] acquired on the spectrometer. In case of the EELS measurements, the first column is the electron energy loss in [eV] and the second column represents the intensity in counts per second [cts/s] on the CCD camera.