T326 Structure and Evolution of Brittle Faults and Fault Rocks: Physical Properties, Geometry, and Geochemical Changes that Influence Water, Energy, and Mineral Resources

Wednesday, 30 October 2013
8:00 AM - 12:00 PM
Room 507

UNDERSTANDING THE EVOLUTION OF LOW STRAIN FAULTS AND FAULT DAMAGE ZONES WITH MICROSCALE TRACE ELEMENT MAPPING

Paper number: T326-3
Program: Technical Sessions
Time: 8:35 AM – 8:50 AM

Authors

Abstract

The Appalachian basin is a relatively undeformed foreland basin that contains significant water and energy resources. In this low-strain setting, thrust faults that accommodate only small amounts of strain are significant, and these faults can dominate their surroundings. These small displacement faults may play multiple important roles: they can alter the hydraulic properties of important aquifers and hydrocarbon reservoirs by acting as pathways or barriers to fluid flow, and they can alter the mechanical properties of rock. The Seneca Stone thrust is an example of a low strain fault that is well exposed in a quarry near Seneca Falls, NY. A well developed damage zone surrounds this small offset (~5m) thrust fault where it cuts through the Onondaga limestone and into the Marcellus shale. This damage zone is characterized by a dramatic increase in the density of calcite veins. These calcite veins dip gently (22˚) to both the North and South and strike E-W (080˚), or roughly parallel to the strike of the Seneca Stone thrust. These gently dipping veins contain both blocky and fibrous crystals and slickenfibers. Outside of the damage zone, deformation features include: steeply dipping regional joints that form two sets which strike 071° and 145°; two sets of steeply dipping veins that strike 355° and 066°, and E-W striking stylolytes. Cross cutting relationships indicate that veins striking 066˚ formed first and were followed by a period during which N-S striking veins, gently dipping E-W striking veins and stylolytes grew cyclically. In particular, the relationships between stylolytes and veins suggest that veins grew during multiple events.

Because vein filling minerals (e.g. calcite, quartz) incorporate the chemical composition of pore fluids into their structure, periods of vein growth provide a geochemical archive of the evolution of the Seneca Stone thrust. In order to investigate how veins evolved with the Seneca Stone Thrust, we used cryogenic LA-ICP-MS to measure trace element concentrations in multiple calcite veins with different orientations.