Suretta nappe shear zones (2021)

Optical microscopy was performed on Axioskop 40 Zeiss microscope under plane and crossed-polarized light. Electron microscopy was performed on a FEI Quanta 450W SEM at the MIMENTO plateform belonging to the French RENATECH network. Observations were performed under backscattered electron images.

Crystallographic preferred orientations (CPO) of quartz were determined by electron backscattered diffraction on single spots or over a gridded area. Single spot analysis were carried out on a scanning electron microscope (SEM) Tescan Vega 2 XMU Low Vacuum at the Ecole et Observatoire des Sciences de la Terre of Strasbourg, France, using the electron backscattered diffraction method (EBSD, coupled with TSL OIM Analysis software). The map was carried out on a SEM JEOL JSM-5910 LV associated with a Bruker Nano, Quantax CrystAlign EDS-EBSD, at the Laboratoire Magmas et Volcans of Clermont-Ferrand, France. A step size of 0.83 m m on a 800 x 600
pixel map was used, so that deformation within the small quartz grains (<25 m m), can be detected. EBSD patterns were indexed and processed with the Bruker Esprit 1.9.4 EBSD software.

Forward phase relation modelling was computed with Perple_X 6.6.8 (Connolly, 2005) in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-O system using the updated 2002 version of the internally-consistent thermodynamic database of Holland and Powell (1998). The system is assumed to be water saturated in order to enhance chemical mass transfer. The oxidation state has been quantified using P-XFe2O3 phase diagram section
computed at 450°C (XFe2O3 = Fe2O3 /(FeO + Fe2O3)). Bulk compositions were computed with an average protolith composition based on 17 XRF analysis from Challandes (2001) and (2) a local effective composition quantified on the mature shear zone affecting the matrix. This local composition has been estimated with high-resolution quantified electron microprobe X-ray maps using the XMaptools 1.6.5 software. Solid solutions are provided in a table