Volcanism, age, and hydrothermal deposits of the West Valley Segment, Juan de Fuca Ridge

Abstract

West Valley is a rift valley that forms part of the northernmost segment of Juan de Fuca Ridge. The valley is about 8 km wide, has a relief of 400–800 m along the valley walls, and has been interpreted to have formed recently by tectonic collapse. As part of a comprehensive study of West Valley, photographic images were obtained using a deeply towed camera sled containing a black and white video camera and a colour 35 mm camera. Photos were analyzed for volcanic form and type, tectonic features, and the relative age of the sea floor. Pillow and lobate lavas were the most common flow types observed. Based on sediment cover and an estimate of the hemipelagic sedimentation rate, the flows may be as young as a few hundred to as old as 2000 years. The youngest lavas are associated with small axial volcanoes that form an en echelon pattern within the valley. Newly discovered hydrothermal sulphide mounds and chimneys are spatially associated with moderately young pillow and lobate flows near the base of a small axial volcano. The area is moderately tectonically disrupted, with the most pervasive tectonism localized at the margins of the valley.