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Keywords:

Paleofluid, Fault zones

Abstract:

In this contribution we describe the structural anatomy and paleofluid flow evolution of strike-slip compartmentalized extensional fault zones developed in the E-W trending Jabal Qusaybah inversion anticline, at the western termination of the Salakh Arc salient, in the Oman Mountains. The Jabal Qusaybah anticline is characterized by a complex fault pattern developed in layered Cretaceous carbonates (Natih formation) dominated by NE-SW left-lateral strike-slip and N-S extensional fault zones. N-S striking extensional fault zones are best developed in the central region of the fold crest, likely due to late-stage outer-arc extension parallel to the fold axial strike. They have displacements ranging from few dm up to ~60 m, and maximum trace lengths ranging from few m up to ~800 m. They generally abut NE-SW left-lateral strike-slip fault zones. Both extensional and strike-slip fault strands show widespread evidence for substantial dilation in the form of (1) dm- to m-thick dilation breccias with mosaic to chaotic textures, and (2) multiple infilling events by large columnar calcite crystals and aggregates. Dilation breccias and fault infillings are localized at fault intersection areas, fault jogs and extensional fault tips. Cross-cutting relationships and petrographic features of fault-related calcite veins and fault-infilling calcite crystals suggest that strike-slip and extensional faulting occurred mostly coevally along with the growth of the anticline. However, fault abutting geometry, and detailed relative chronology and 13C and 18O signatures of vein and fault infillings indicate that extensional faulting associated with longitudinal outer-arc extension was a late stage event, mainly postdating the strike-slip faults. Fluid inclusion data on different generations of calcite fault infillings indicates temperature of 75-115°C in the strike-slip fault zones, and temperature < 60°C mostly associated with the extensional fault zones. These data suggest that, during the growth history of Qusaybah anticline, deep seated regional strike-slip faults channelized hot fluids, whereas late-stage and more shallow extensional faults provided the preferential pathways for a second fluid flow episode. These data have important implications to predict locations of areas of enhanced fault connectivity in structurally complex, fold-related carbonate reservoir.