Deciphering tectonic evolution: Discrete element modeling reveals mechanism of the Qiyueshan Fault within the Xuefengshan foreland thrust belt, South China

A pioneering study published in Geoscience—a premier journal advancing cutting-edge research in tectonics and Earth system sciences—has unveiled critical insights into the formation and structural role of the Qiyueshan Fault, a major tectonic boundary within China’s Xuefengshan foreland fold-and-thrust belt. Conducted by researchers from the China University of Geosciences (Beijing), the study employs discrete element numerical simulations integrated with seismic reflection data to resolve longstanding debates about the fault’s origin and its control over regional deformation patterns.

The Qiyueshan Fault, a northeast-trending structure, demarcates the transition between the Northwestern Sichuan box-like fold-thrust belt and the Southeastern Hunan trough-like belt. Despite its significance as a traditional boundary between the Middle and Upper Yangtze Blocks, the fault’s formation mechanism and its influence on differential deformation have remained poorly understood, fueling divergent theories about the broader tectonic evolution of South China. Previous hypotheses proposed competing models, including pre-existing fault reactivation versus detachment-layer-driven deformation, but lacked conclusive evidence.

To address this, the research team designed five discrete element numerical models, systematically testing variables such as pre-existing fault geometry, detachment layer thickness, and mechanical properties. Simulations revealed that pre-existing faults localize strain, dictating fault activation sequences and deformation propagation. In contrast, models without pre-existing faults demonstrated that weak basal detachments dominated stress transfer, while thicker intermediate detachments facilitated mechanical decoupling between rock layers. These findings highlight the critical role of multi-layered detachments in forming the “double-step” fault-bend folding architecture.

Crucially, the study concludes that the Qiyueshan Fault is not a pre-existing structure but emerged during progressive deformation. Its formation was governed by the interplay between the lower Cambrian detachment layer and the basement detachment: deeper, mechanically weaker detachment controlled the development of the Hunan trough-style folds, while shallower detachment shaped the Sichuan box-like folds. This mechanical decoupling explains the fault’s role as a transitional boundary and its impact on hydrocarbon reservoir distribution—a discovery with direct implications for energy exploration in structurally complex regions.

The research bridges observational geology and computational modeling, offering a dynamic framework to analyze multi-layered detachment systems in fold-thrust belts globally. By clarifying the Xuefengshan belt’s evolution, the study advances understanding of intracontinental deformation mechanisms, particularly in regions shaped by polyphase tectonics. These insights are pivotal for predicting subsurface structures, assessing seismic hazards, and optimizing resource exploration strategies, underscoring the societal relevance of geodynamic research.

This work exemplifies the transformative potential of integrating numerical simulations with field data. The findings not only resolve regional tectonic controversies but also establish a methodology applicable to analogous systems worldwide, reinforcing the importance of interdisciplinary approaches in decoding Earth’s complex architectures.