FAULT DAMAGE ZONE AND CORE FRACTURE POROSITY DIFFERS IN ADJACENT SANDSTONES OWING TO INHIBITED QUARTZ ACCUMULATION ON FELDSPAR AND LITHIC GRAIN SUBSTRATES

Adjacent Latest Precambrian lithic arkose to feldspathic litharenite and Cambrian quartz arenite sandstones in NW Scotland that are cut by the same m- to decimeter displacement oblique slip faults have damage zones and fault cores that differ markedly in the length, aperture, arrangement, and degree of porosity preservation of constituent fractures despite sharing the same slip and thermal history. The location of likely open flow conduits and weak fault rock switches across the rock type boundary from the fault damage zone in lithic arkose/feldspathic litharenites to the fault core in quartz arenites. The contrast likely reflects inhibited quartz precipitation on feldspar and lithic grain substrates on fracture walls, and implies that diagenetic self-sealing and hardening of faults varies along fault surfaces with host rock type.