High-Temperature Deformation in the Tan-Lu Fault Zone: Constraints on an Early Cretaceous Transtensional Regime

How continental lithosphere stretches and ruptures is a fundamental question in Earth sciences; however, effective constraints on the physical conditions deep within the crust where deformation is concentrated remain elusive. This study offers new insights into this process through a detailed dissection of the Tan-Lu Fault Zone, one of the most extensive fault systems in East Asia. A critical controlling factor for crustal rheological properties is deformation temperature, a challenge we address by employing a thermometer based on the fractal dimension (D-value) of dynamically recrystallized quartz grain boundaries. Analyzing 62 mylonite samples from the Feidong segment, we reveal that left-lateral strike-slip shearing along this fault zone occurred under high temperatures (~450–700 °C). This conclusion is not only derived quantitatively from a quartz D-value thermometer but is also visually corroborated by classic high-temperature microstructures (e.g., extensive grain boundary migration), corresponding to conditions from the upper greenschist to amphibolite facies. Existing geochronological data constrain this high-temperature shearing event to the Early Cretaceous. Such elevated temperature conditions, combined with field and microstructural evidence indicating extension, provide quantitative confirmation that the fault zone operated within a transtensional tectonic regime during that period. Our findings offer a rigorously thermally constrained dynamic model for the deformation behavior of large continental faults during large-scale lithospheric thinning and craton destruction, providing a valuable framework for interpreting crustal rheology and continental dynamics.