A new technique for quantifying symmetry and opening angles in quartz c-axis pole figures: Implications for interpreting the kinematic and thermal properties of rocks

Deformational, crystallographic and petrochronological analyses of the mylonites from Taxaquara shear zone in Ribeira Belt (São Paulo)

“…In this study, the CPOs are used to determine slip-system activated during quartz deformation, deformation temperature through opening-angle (OA) thermometer (Faleiros et al, 2016a(Faleiros et al, , 2016b and vorticity studies (δ/βmethod; . Data were further processed using MTEX (https://mtex-toolbox.github.io/) toolbox in MATLAB to quantify OA and the vorticity plane following (Hunter et al, 2018).…”

“…The δ/βmethod depends on the relation between the maximum angle (δ) between quartz oblique and main foliations in combination with the angle (β) between the shear plane and principal foliation determined through quartz [c] axis fabric. The measurements of β angles were carried out through a MTEX code developed in MATLAB environmental (Hunter et al, 2018) which estimate the vorticity plane based on the difference the foliation plane (E-W) and…”

“…Quartz CPO fabrics also suggest the same variation. Monoclinic patters are related with non-coaxial deformation (i.e., simple shear), while orthorhombic fabrics indicate coaxial plane strain (i.e., pure shear) (Hunter et al, 2018a(Hunter et al, , 2018bSchmid and Casey, 1986). The dominance of simple shear over pure shear from δ/β vorticity method and quartz [c]-axis monoclinic over orthorhombic fabrics suggest that TSZ developed under a sub-simple shear system .…”

“…In this study, the CPOs are used to determine slip-systems activated during quartz deformation, deformation temperature through opening-angle (OA) thermometer Faleiros et al, 2016a) and vorticity (δ/β -method; . Data were further processed using MTEX (https://mtex-toolbox.github.io/) toolbox in MATLAB to quantify OA and the vorticity plane following (Hunter et al, 2018a) In addition to FA analysis, we analyzed one mylonite sample (PS-41A) using electron backscattering diffraction (EBSD) technique to compare with the FA results to ensure CPO quality and proper quantification of the slip systems activation during deformation based on axis misorientations (Neumann, 2000;Wheeler et al, 2001). Measurements were made using a 15 kV acceleration voltage, 13.7 mm working distance and 70°sample tilt.…”

“…In this scenario, the mineral equilibria-based geothermobarometry and thermodynamic modelling helps to precisely constrain the P-T conditions in which the rocks were deformed. Quantification of microstructures, supported by petrological analyses, is a useful tool in determining deformation conditions in quartz-feldspathic deformed rocks such as granitic mylonites, particularly when appropriate mineral assemblages that might constrain metamorphic conditions are rare (Faleiros et al, 2010;Cavalcante et al, 2018;Hunter et al, 2016;Hunter et al, 2018aHunter et al, , 2018b.…”