Clastic Dikes as Conduits for Episodic Fluid Flow in the Upper Crust

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9304581 Boles The proposed study seeks to identify and quantify processes by which clastic dikes serve as conduits for episodic and rapid fluid flow in the upper crust. This study will investigate transport mechanisms for breccia components in clastic dikes in silicious shales of the Miocene Monterey Formation, coastal California, and in Paleozoic limestones both in Titus Canyon, Death Valley, and in the Shell Creek Range, NE Nevada. Minimum velocities of fluid flow will be calculated using relations among flow velocity, clast size, viscosity, and fluid and clast densities in fluidized beds. These parameters will be estimated based on field and thin section investigators, fluid inclusion studies, and published density values of similar rock types. Episodic fluid flow through the dike can be inferred if the calculated flow velocity through the dike is much faster than seepage by darcian flow. In addition, mechanism leading to fragmentation of wall rock and breccia components in clastic dikes will be investigated. Identification of the latter process would allow estimated on the magnitude and rate of drops in pore pressure. Rapid drops are considered as characteristic for clastic dikes serving as conduits for large scale, episodic fluid flow. Stable isotope and trace element measurements across crack seal veins associated with clastic dikes will determine if the dikes were chemically closed or open systems. Strontium isotope analyses of wall rock and vein filling minerals will indicate if vein cementation occurred in a closed or open system. The proposed investigations will increase the present understanding of fluid flow mechanisms within the upper crust. Findings of this study may influence research in applied fields such as transport of contaminants and heat in fractured rocks of earthquake hazard analysis. ***