Testing predictions of fracture patterns in fold and thrust belts: a case study from the Salakh Arch, Oman

Structural restoration and the forward models that can be developed from them, provide tools for predicting fracture patterns in folded strata within compressional regimes. Here we test predictions made from 2D restorations of a foreland fold and thrust belt, the Salakh Arch of the northern Oman Mountains. The Arch is represented by km-scale periclines interpreted as buckles of the 3 km inter-bedded limestone and shales sequence, detached on a regionally-extensive evaporite horizon. Results from this study indicate that fractures relate to the orientation of the local structure, with some sets parallel and some sets perpendicular to local hinge lines. The majority of fractures have orientations consistent with having formed by flexural slip/flexural flow on fold limbs. These structures can be predicted from finite stratal dip, simple curvature and 3D folding restoration maps whereas Gaussian curvature and 3D faulting restoration maps can be used as proxies for fault-related fractures. Local hinge-related fractures may reflect local tangential longitudinal strain during large- scale fold-tightening. Those fold structures that have formed oblique to the regional shortening direction show additional hinge-perpendicular fracture arrays indicating weak axial extension, presumably developed as the arcuate thrust belt amplified. Our analysis illustrates the importance of taking a 3D approach, especially within non-cylindrical fold systems, and in discriminating between local and regional deformation fields. The protocols developed in this study and their results, as applied to the Salakh Arch, may have general applicability to the investigations of fracture patterns in other fold segments.