Unraveling the influence of throw and stratigraphy in controlling subseismic fault architecture of fold-thrust belts: An example from the Qaidam Basin, northeast Tibetan Plateau

Abstract

Understanding the detailed fault architecture of reverse faulting is critical for understanding the processes involved in fold-thrust belts as well as predicting the degree of fault compartmentalization, the relationship between folds and faults, the distribution of strain, and subseismic faulting deformation. The Lenghu5 fold-thrust belt provides an exceptionally well-exposed outcrop example of a reverse fault-related fold. Detailed stratigraphic logging coupled with high-resolution cross sections provides a unique insight into the three-dimensional geometry of a thrust fault at both basin and outcrop scale. In this study, we observe that 85%–90% of the estimated throw is accommodated on the main fault zone, which has sufficient throw to be imaged on a seismic profile, whereas 15%–20% of the throw is accommodated on smaller-scale folds and faults that are beyond seismic resolution. The plan-view mapping of the structure reveals that there is significant variation in how strain is accommodated along the structure, which is associated with the throw variations in the main fault. In addition, by coupling the structural observations within a stratigraphic context, we can demonstrate that although the main fault controls the overall strain in the system, the local stratigraphy plays a critical role in how the strain is accommodated and whether it is partitioned into single faults, multiple-fault splays, or folding. By demonstrating the remarkable geometric similarity between the outcrop observations with a comparable structure in the subsurface (Niger Delta), the study provides an insight into the potential subseismic fault-zone geometry present in poorly imaged fold-thrust systems.