Landward vergence and oblique structural trends in the Oregon margin accretionary prism: Implications and effect on fluid flow

摘要: Abstract The central Oregon margin spans a regional transition in accretionary structures from seaward-verging the south to landward-verging north. New multichannel seismic (MCS) data image both landward- and seaward-vergent provinces along northern margin. Landward-vergence is characterized by deep decollement, with deformation distributed across broad lower continental slope coherent structural style. In landward-vergent area, virtually all 4 km of incoming trench sediments overthrust preceding thrust sheet, forming fault-bend folds distinctive ridge/trough morphology. This style landward-vergence not explained existing models. contrast, seaward-vergence correlates shallower approximately 1.4 above oceanic crust, more intense within narrower slope. Initial thickening occurs well-developed protothrust zone. frontal forms ramp-anticline that cut prominent backthrust. Previously observed seafloor vent sites regions correlate thrusts exhibit high-amplitude, reversed-polarity reflections suggestive enhanced porosity faults. Potential fluid sources migration paths are strongly influenced changes level decollement vergence Abrupt occur strike updip, bounded two sets oblique-slip Three NW-striking left-lateral faults imaged MCS SeaBeam data. Plunging anticlines developed venting fluids were previously interpreted as mud volcanoes. front locally disrupted where these intersect prism, but they appear have limited influence on evolution prism. NE-striking right-lateral confined deforming upper plate. These interact rhomboidal pattern three-dimensional deformation.