Seismic and Thermal Structure of the Subducting Yakutat Block Microplate, Southeast Alaska
The convergent motion of the Pacific and North American Plates in Alaska has produced geologic features associated with subduction zones such as trench, Wadati-Benioff zone, and volcanic arc along the Aleutians and has transported displaced terranes along the Queen Charlotte fault that forms the northeastern boundary of the Pacific Plate. These subduction features stop abruptly at the edge of the Yakutat Block displaced terrane, approximately 300 km from the Queen Charlotte-Fairweather fault. The purpose of this study was to determine the geometry of the Yakutat Block and North American boundary as well as the cause of the offset volcanic arc and missing Wadati-Benioff zone.
We calculated P and S receiver functions for broadband seismic stations located in southeast Alaska. S-wave data was migrated using a Common Conversion Point procedure. P-wave data was imaged via a three-dimensional, pre-stack migration using plane-wave decomposition. We calculated the temperatures at the top of the Yakutat slab and mantle wedge using analytical models.
The 3-D images we produced show that the Yakutat and Pacific slabs are continuous and extend to the Queen Charlotte-Fairweather strike-slip fault systems. The subducting slab extends north at least to the Wrangell Volcanic Field with a dip than increases gradually from 10° near Prince William Sound to 15° near Yakutat Bay, stripping approximately 15 km of overlying sediments. The location of the Wrangell Volcanic Field and lack of Wadati-Benioff zone are consistent with the temperatures we calculated for the top of slab and mantle wedge after stripping 15 km of sediment.
AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013