GOLDFINGER, C; M. E. TORRES, and A. M. TREHU
all at COAS, Oregon State University

Abstract: Possible Strike-Slip Fault Source for Hydrate Ridge Methane Vents, Cascadia Margin

Vigorous streams of methane bubbles from decomposition of gas hydrates have been previously observed to emanate at the seafloor on Hydrate Ridge during Alvin dives in 1989 and during a ROPOS survey from the RN Sonne in 1996. Detailed observations of the seafloor during the most recent ROPOS cruise to the area in 1998 revealed that the sites of active gas discharge line up within a narrow band trending 111 degrees. This feature approximately parallels larger mounds imaged by Seabeam as well as strike-slip faults of the accretionary prism. Just 12 km north of the vent sites lies the projected trace of the Daisy Bank fault, a major sinistral strike-slip fault striking 110 to 120 degrees. This fault offsets the Juan de Fuca basement seaward of the deformation front, and is inferred to continue beneath the accretionary wedge, where it can be discontinuously traced to the continental shelf edge. Similarly aligned carbonate deposits and seeps have been observed along the Daisy Bank fault at Daisy Bank on the upper slope. Shearing of northern Hydrate Ridge by strike-slip faulting may provide deep conduits to underlying subducted and underplated sediments as found at the related Wecoma strike-slip fault approximately 30 km to the north. The observation that the gas seeps show the same azimuth as these faults suggests that hydrate destabilization and gas discharge along vents on Hydrate Ridge may be related to strike-slip faulting.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California