HR: 11:05h
AN: T12B-04    [Abstracts]
TI: Synkinematic veining and thermal transect across a formation-bounding out-of-sequence-thrust, Kodiak Accretionary Complex
AU: * Rowe, C D
EM: crowe@es.ucsc.edu
AF: UC Santa Cruz, Dpt. Earth Sciences, 1156 High St., Santa Cruz, CA 95064 United States
AU: Moore, J C
EM: cmoore@es.ucsc.edu
AF: UC Santa Cruz, Dpt. Earth Sciences, 1156 High St., Santa Cruz, CA 95064 United States
AU: Meneghini, F
EM: meneghini@dst.unipi.it
AF: Universite di Pisa, Dipartimento di Scienze della Terra, via S. Maria, 53, Pisa, 56126 Italy
AU: McKiernan, A W
EM: amckiern@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, 320 Deike Building, University Park, PA 16802 United States
AB: A large, formation-bounding out-of-sequence thrust outcrops on Afognak Island, Kodiak Islands, Alaska. The uppermost footwall is deformed by thin, highly sheared veined zones at close intervals beneath the formation bounding fault, decreasing in size and frequency rapidly below the fault. Field observations of the thrust interface suggest that the Uganik Thrust has a complex history including multiple episodes of reverse motion and more recent oblique-slip motion. Intrusive dikes indicate that the Uganik Thrust was primarily active in latest Cretaceous to early Paleocene time as an out-of-sequence thrust, and this motion was accompanied by the development of high fluid flux surfaces, parallel to and within the footwall of the thrust (Kodiak Fm). These surfaces manifest in outcrop as highly sheared zones with 10-100x greater density of synkinematic veining than elsewhere within the fault zone, which itself has 10x greater vein density than the background footwall rocks. Deformation in the hanging wall (Uyak Melange) is distinguished by the development of a discontinuous narrow zone of mylonitic fabric but no significant vein or cement precipitation in the hanging wall. These high-shear, fluid-focusing surfaces rapidly decline in frequency, magnitude, and thickness below the Uganik thrust. Three generations of veins are preserved in the vicinity of the fault, recording early stratal deformation, syn-tectonic shearing, and finally, post-fault intrusive events. Fluid inclusion measurements indicate shear vein homogenization temperatures are distinctively hotter (approx 240 +/- 20C) than homogenization temperatures of later veining events (193 +/- 25C). The Uganik Thrust was active within <7 My of subduction of the affected rock units. The vein density associated with the Uganik Thrust is many times larger than the other preserved thrust faults in the Kodiak Accretionary Complex. This reflects either significantly greater fluid transport in the Uganik Thrust, or more rapid (non-equilibrium) fluid transport, in order to precipitate a great concentration of quartz veins during fault activity.
DE: 1043 Fluid and melt inclusion geochemistry
DE: 8021 Melanges
DE: 8025 Mesoscopic fabrics
DE: 8045 Role of fluids
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: Fall Meeting 2005