## 2 Materials and Methods
### Methods  
This study used a variety of analytical techniques to examine the microstructure and chemical composition of the samples, including Optical Microscopy, scanning electron microscopy (SEM)-Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), X-ray Diffraction (XRD), X-ray Fluorescence Spectroscopy (XRF), and Electron Probe Micro-analysis (EPMA).  
Polarizing Microscope & SEM-EDS: Microstructures of the samples were observed using a polarizing optical microscope (LEICA) and a scanning electron microscope (Zeiss SIGMA) (SEM) at the State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China. The SEM equipped with an Oxford X-Max 50N energy-dispersive X-ray spectroscopy (EDS) were used for measuring element composition, respectively.  
EBSD: The quartz fabrics were measured by SEM-EBSD analysis using a scanning electron microscope (SEM) coupled with an Oxford Nordlys nano electron backscattered diffraction (EBSD) detector at the State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China. Polished thin sections were carbon-coated prior to EBSD analysis. EBSD allows for the determination of the full crystallographic orientation of crystals in a thin section using a backscattered electron (BSE) signal. Automatic EBSD measurements were used to obtain orientation maps and crystallographic preferred orientation (CPO) patterns. Working conditions during acquisition of the EBSD patterns were 20 kV accelerating voltage, 12 nA probe current, 70\({}^{\circ}\) sample tilt, \(\sim\)20 mm working distance, and high vacuum. EBSD patterns of quartz were acquired and indexed with HKL AZtec software (Oxford Instruments), which selected the direction of the stretching lineation as the X-axis direction; that is, the quartz-mica strip direction is the X-axis direction, and the plane-oriented direction is the XY-plane direction. CHANNEL 5 software (Oxford Instruments) was used for noise reduction and for filling the missing data with at least eight identical neighbors with similar orientation. All stereographic diagrams of EBSD are lower hemisphere projections.  
XRD: XRD analysis was performed to qualitatively identify mineral compositions in pseudotachylyte samples and host rocks, XRD data were collected using Bruker D8 ADVANCE X-ray diffractometers with Cu K\(\alpha\) radiation over the 20 range of 3\({}^{\circ}\)-70\({}^{\circ}\), with a step size of 0.02\({}^{\circ}\) at the Beida Zhihui Microstructure Analytical Center in Beijing.  
XRF: Whole-rock chemical analysis of major elements in pseudotachylyte and host rocks using a Magix-pro2440 XRF machine at theInstitute of Geology, Chinese Academy of Geological Sciences.  
EPMA: Major element compositions of mineral grains were determined using a JEOL JXA-8230 electron probe micro-analyzer (EPMA) at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences. The analytical conditions were 15-kV accelerating voltage, 20-nA beam current, 5-\(\upmu\)m probe diameter, and 5- to 10-s counting time (background and peak) per element. EPMA analyses were performed on 10 grains for each mineral.  
The above methods are described in detail in the following Table 1.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Analytical Method** & **Research Objective** & **Technical Features** & **Co-Application Necessity** \\ \hline \multirow{3}{*}{Polarizing microscope} & Pseudotachylyte & Macro-scale structural resolution & \\  & morphology observation & (50–500 \(\upmu\)m) & \\  & Micro-deformation analysis & & \\ \hline \multirow{3}{*}{SEM-EDS} & Mineral assemblage quantification & Micron-scale morphology & Morphology \\  & Micro-fracture & imaging (1–50 \(\upmu\)m) & composition co-analysis \\ \cline{1-1}  & filling characterization & Elemental mapping & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Analytical methods and co-application necessity.