The Meso-Cenozoic fracture pattern of the Lurestan region, Iran: The role of rifting, convergence, and differential compaction in the development of pre-orogenic oblique fractures in the Zagros Belt

Abstract

In this work we present data on fractures and mesoscale folds exposed in the Triassic to Miocene sedimentary succession of the Lurestan region (Zagros Belt). Data have been collected in tens of field sites, in a 104 km2 area extending across the High Zagros Zone and the Folded Belt. Fractures and mesoscale folds have been characterised in terms of orientation, cross-cutting and abutting relationships with the other structures, and relative timing with respect to sedimentation. Outcrop-scale folds, stylolites, and reverse faults are NW-SE oriented and developed during NE-SW directed shortening. Extensional fractures, including joints, veins, and normal faults, are arranged into two assemblages including: (i) NE-SW and NW-SE striking fractures and (ii) NNW-SSE and WSW-ENE striking fractures. Syn-sedimentary fractures of the two extensional assemblages occur in pre- and syn-rift Jurassic rocks, but also in post-rift Cretaceous rocks and Cenozoic syn-orogenic rocks. We infer that the development of these extensional fractures in the Lurestan region was controlled by: (i) NE-SW-directed extension during both Early Jurassic rifting and early orogenic foreland extension; and (ii) WSW-ENE-directed stretching caused by differential compaction and related subsidence above NNW-SSE elongated basement structures, during tectonically quiescent periods.