Study on the Tectonic Stress Control Mechanism of Graphitization in Carbonate Rocks

Graphite is commonly found in seismic slip zones and ductile shear zones, and it has traditionally been thought to form through the graphitization of organic matter or through fluid-mediated reduction. Recent studies have identified shear action as playing a significant role in the transformation of carbonate rocks into graphite, yet the stress-related chemical origins of this process remain unclear. This research employed both constant and incremental speed friction experiments using limestone and marble, combined with X-ray Diffraction (XRD), Raman Spectroscopy, and Total Organic Carbon (TOC) analysis, to explore the potential for and the stress-chemical causes of graphitization in carbonate rocks within shear zones. The experimental results demonstrate significant structural transformations of carbonate rocks under shear stress. Limestone is more prone to graphitization during deeper plastic deformation phases, whereas marble tends to graphitize during shallower brittle deformation stages. Furthermore, the findings indicate that compared to a single tectonic event, complex multi-phase tectonic structures are more likely to enhance the degree of graphitization in carbonate rocks. This study enriches the theoretical understanding of graphite formation and occurrence, provides scientific insight into the weakening of the crust and the mechanisms of seismic slip, and reveals the micro-mechanisms of carbonate rock graphitization under tectonic stress. It highlights that metamorphic effects on mineral structure and chemical bonds are critical factors affecting graphitization at different deformation stages.