Electron-beam dose dependence of the non-bridging oxygen hole centre in quartz across diverse rocks and sediments revealed by scanning electron microscopy: potential implications for provenance and thermochronology

Status note: This manuscript has been submitted to Chemical Geology and is currently under peer review Abstract: Despite being one of the stoichiometrically purest minerals (ideal formula SiO₂), quartz exhibits various intrinsic and impurity-related defects that contain important genetic information. We report scanning electron microscopy (SEM) coupled with cathodoluminescence (CL) wavelength-resolved spectroscopy on quartz from different rock types spanning a wide range of geological settings and ages to investigate defect phenomena. All samples show two main emissions: a red band at ~1.93 eV (~643 nm), attributable to non-bridging oxygen hole centres (NBOHC) defects, and a blue band at ~2.7 eV (~450 nm), explained by Ti-related defects. The origin of NBOHCs is relatively well understood and may result from intrinsic mechanisms or extrinsic pathways involving radiolysis of passivated precursor sites such as hydroxyl-related defects. Radiation-damage experiments under controlled electron irradiation in SEM provide a tool to study defect formation dynamics. We investigate the evolution of the NBOHC defect at different irradiation times (electron doses). CL acquired during SEM irradiation shows monotonic growth of the ~1.9 eV emission described by the sum of two saturating exponentials, interpreted as coexistence of hydroxyl-mediated defect generation and intrinsic rupture of Si–O–Si bridges or peroxy Si–O–O–Si linkages. SEM-induced NBOHC luminescence is therefore controlled by the balance between hydrogen chemistry and intrinsic bond rupture, reflecting quartz geological type. The initial CL intensity records the natural balance among α-radiation damage, thermal resetting, and hydrogen passivation. These relations suggest NBOHC CL as a potential quartz-intrinsic provenance indicator or thermochronometer.