In this paper. the diagenesis from either side of a major Cenozoic reverse fault in the Northern Oman Mountains is documented. Detailed petrographical and geochemical analysis of calcite-filled fractures in carbonate strata of Late Triassic and Early Cretaceous age in the hanging wall and footwall in Wadi Ghalilah reflect a different diagenetic history. In both hanging wall and footwall most of the fractures are pre-burial, extensional in origin, formed by a crack-seal mechanism, and the calcite vein infill has a host-rock buffered signature. In the hanging wall, the fluid responsible for calcite precipitation of these extensional fractures was a marine fluid at 60 degrees C. These veins predate deep burial and contractional tectonic deformation and consequently do not provide any information about syntectonic fluid flow. Neither do the pre-burial extension fractures in the footwall which are also host-rock buffered. The fractures postdating the tectonic stylolitization in the footwall, by contrast. show evidence of syntectonic migration of saline formation waters at temperatures between 80 and 160 degrees C during contractional deformation. These fluids probably were sourced from the Subsurface via the reverse fault. which acted as a fluid conduit. At the same time, however, this fault functioned as a permeability barrier towards the hanging wall. since no evidence of syntectonic fluid flow is present here. In this way compartmentalization of the hanging wall and footwall block was realized. (C) 2007 Elsevier Ltd. All rights reserved.
