Abstract

The damage zone of three small faults in the Navajo and Page formations, located on the NE side of San Rafael Swell, Utah, USA, are studied. Scanlines and microstructural analyses are used to document three distinct deformation events: (1) an early phase creating cataclastic deformation bands, during which most of the displacement on the fault took place; (2) a fracturing event with opening and shearing along fractures; and (3) fluid flow and local calcite precipitation along the NW-trending faults. Microstructural characterization of deformation structures shows complex interaction between deformation bands, fractures and the calcite precipitation. Calcite cement is observed as veins in the host rock and along cataclastic bands, with varying amount of cataclastic material floating within the veins. In addition to patchy calcite cement in the host rock, extensive poikilotopic cementation is observed to extend into cataclastic bands with a low degree of cataclasis. However, some cataclastic bands with a high degree of cataclasis show almost no cementation. Development of deformation bands and their link to fracturing affected the flow field, from a fault baffle to a conduit. Calcite cementation reveals the flow paths, before cementation recreated the fault baffle.

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