Granite Fabrics and Paleostress: An Integrated Structural Approach to Felsic Plutonites

The weak anisotropic fabrics of granites can be used to reconstruct emplacement and strain conditions to infer the paleostress field during their development. For that purpose, case studies commonly analyse the anisotropy of magnetic susceptibility (AMS) or the crystallographic preferred orientations (CPOs) of rock-forming minerals. Here, we present a systematic investigation of a range of granitoids from Germany, integrating AMS data with CPOs of feldspar and quartz (EBSD) and universal-stage measurements of microfracture orientations. Primary magmatic fabrics, as defined by AMS and feldspar CPOs, exhibit local variability in orientation and range between prolate and oblate shapes. In contrast, late- to post-magmatic fabrics are revealed through fluid inclusion planes (FIPs) and quartz CPOs. While c-axis distributions in low-strain samples are typically weak and irregular, distributions of the rhomb-faces consistently display orthotropic symmetry, characteristic of stress-induced Dauphiné twinning. These patterns, previously proposed as potential paleostress indicators, align systematically with FIP orientations, which are independently known to record coaxial strain at low differential stresses. Remarkably, both rhomb-face distributions and FIP orientations are spatially consistent across several kilometres, highlighting their potential as mappable late- to post-magmatic paleostress indicators. We discuss the implications of these findings for regional paleostress interpretations and the role of late-magmatic fluid migration pathways during the structural evolution of granites.