Nanoscale insight into tribomechanical and hydrothermal process at calcite surface
Fault slip and earthquake nucleation are controlled by interfacial processes that operate at the nanoscale, where chemical, mechanical, and thermal effects converge to regulate frictional behavior. Among the minerals that compose the lithosphere, calcite is particularly significant due to its abundance, ductility, and reactivity in aqueous environment. The induced dissolution and precipitation, commonly described as pressure solution and cementation, actively reconstruct calcite surfaces and are hypothesized to play a decisive role in modulating frictional response in carbonate-rich faults. Yet, the mechanisms linking nanoscale interfacial processes with macroscopic fault slip remain poorly understood. Our goal is to investigate the tribomechanical behavior of calcite and provide fundamental understanding to connect nanoscale interfacial dynamics with macroscopic fault mechanics. To achieve this objective, the following specific goals were accomplished: I. Characterize ion-specific effects on pressure solution–facilitated slip II. Determine the effect of roughness on the friction and pressure solution III. Explore the tribomechanical process under hydrothermal conditions IV. Quantify and model the mechanochemical and tribomechanical process of calcite within the framework of rate and state friction (RSF) model To address these aims, surface force measurements-including friction force, hydration force, and Derjaguin–Landau–Verwey–Overbeek (DLVO) forces-were performed by atomic force microscopy (AFM) in various conditions. Load-dependent friction measurements in Ca²⁺, Mg²⁺, and Ni²⁺ solutions, paired with in situ calcite thickness analysis by Surface Force Apparatus (SFA), revealed that confined fluid chemistry and ion–surface interactions regulate the onset and magnitude of pressure solution, thereby affecting frictional strength. Velocity-dependent friction studies on polished calcite surfaces of varying grain size demonstrated that nanoscale roughness promotes aseismic slip, whereas the presence of water suppresses the roughness effect by activating pressure solution. The temperature-dependent friction measurements at nanoscale provide thorough insights into the complex change of calcite surface. At elevated temperatures, AFM measurements under humid conditions revealed competition between stick–slip and reduction in energy barrier for thermally activated slip, accompanied by surface reconstruction through hydration layer. In comparison, hydrothermal experiments with calcite probes demonstrated the frictional weakening behavior in solution for the first time, and both the evolution of contact area and bond quality, which is related with changes in interfacial ion structures, were carefully monitored and contribute to advancement in existing RSF model. The findings of this research employed nanoscale evidence to inspect the influence of water, surface roughness, and temperature on the interfacial reactions occurring on calcite, which has advanced the fundamental knowledge of tribomechanical processes at fault interface. These results support the extension of the RSF framework to nanoscale contacts and motivate a generalized friction model that incorporates chemical, mechanical, and thermal effects. In the context of earthquake science, this work helps to identify the microphysical conditions that favor either stable creep or unstable slip in carbonate-bearing faults, contributing to improved models of earthquake nucleation in the seismogenic zone. More broadly, the tribomechanical and mechanochemical understandings can inform strategies for subsurface engineering applications where calcite is abundant, including carbon sequestration, geothermal energy production, and hydrocarbon recovery. By bridging nanoscale processes with fault-scale behavior, this research not only enriches the theoretical framework of rock slip but also provides a scientific foundation for anticipating and mitigating seismic hazards in carbonate-dominated geological systems.
Tribology, Atomic Force Microscopy, Calcite, Pressure solution, Hydrothermal
University of Illinois - Urbana-Champaign
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