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Systematic relationships between the fracture orientation and fold geometry in sedimentry rocks have been used to explain the development of synfolding fractures.Based on field observation at the Khushalgarh syncline,located east of the Kohat plateau,we proposed that the orientation of fractures was influenced dominatly by two tectonic fracture sets, thats is the NE-SW and NW-SE. The NE-SW fracture set dominantly formed as mode I (tensile), where as , the NW-SE fracture set deceloped as mode II (Shear) conjugate fractures. The NE-SW tranding fractures gollow the axis of the syncline, whereas, the NW-SE fracture set crosscuts the fold axis. Most of the NE-SW fractures abut against the NW-SE frature set. Based on the orientation and crosscutting relationships, their modes in response to stress, we conclude that NE-SW trending fractures formed early than those of NW-SE fracture set. Though both the fracture sets are formed during the folding we suggest that they were not formed at the same time. Their crosscutting relationship suggests that they developed sequestially ratehr than synchronously. Our interpretations support the laboratory-based models where only one fracture orientation (or set of fractures with one orienctaion) form in response to single stress. However as the stress distribution in folded strate changes over time,new fractures of distinct orientations can form during or late in the folding history.We conclude that the sandstone units underwent bedding-parallel extension during folding,where bedding is stretched to accommodate extension,parallel to the fold axis orientation.Bending of the limbs is a likely mechanism for the development of observed NE-SW trending fractures during folding,whereas the NW-SE fractures developed late in the folded history.
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