The spatial and temporal evolution of the Portland and Tualatin forearc basins, Oregon, USA

Abstract The Portland and Tualatin basins are part of the Salish-Puget-Willamette Lowland, a 900-km-long, forearc depression lying between volcanic arc Coast Ranges Cascadia convergent margin. Such inland seaways characteristic warm, young slab subduction. We analyzed to better understand their evolution relation Range history provide an improved tectonic framework for metropolitan area. model three key horizons in basins: (1) top Columbia River Basalt Group (CRBG), (2) bottom CRBG, (3) Eocene basement. Isochore maps constrain basin depocenters during Pleistocene mid-Miocene time (0–15 Ma), CRBG (15.5–16.5 early Miocene late (ca. 17–35 Ma) time. Results show that have distinct Quaternary but were one continuous from until A NW-striking gravity low coincident with NW-striking, fault-bounded Hills anticline is interpreted as older graben observed thickening flows underlying sedimentary rocks. Neogene transpression structurally inverted Sylvan-Oatfield normal faults high-angle dextral-reverse faults, separating basins. An eastward shift depocenter ten-fold decrease accommodation space temporal constraints on emergence west. Clockwise rotation northward transport deforming producing local earthquakes beneath