Mid-Miocene to Present Upper-Plate Deformation of the Southern Cascadia Forearc: Effects of the Superposition of Subduction and Transform Tectonics

The southern Cascadia forearc undergoes a three-stage tectonic evolution, each stage involving different combinations of drivers, that produce differences in the upper-plate deformation style. These drivers include subduction, northward migration Mendocino triple junction and associated thickening thinning related to Crustal Conveyor (MCC) effect, NNW translation Sierra Nevada-Great Valley (SNGV) block. We combine geodetic data, plate reconstructions, seismic tomography topographic observations determine how upper is deforming response combined effects subduction NNW-directed (MCC- SNGV-related) processes. location terrane boundaries between relatively weak Franciscan complex stronger Klamath Mountain province (KMP) SNGV block has been key control on style since mid-Miocene. At ?15 Ma, present-day was central there principally controlled by Since ?5 this region plate, where KMP lies inboard complex, both MCC- SNGV-related effects. GPS data show currently moving at ?8–12 mm/yr with little internal deformation, largely push its boundary. In contrast, accommodating high NE-directed shortening strain produced MCC-related coupling respectively. This composite regime can explain faulting within west KMP. Associated crustal thickening, imagery shows low velocity material we interpret represent flow injection crust into intracrustal levels. suggest young feature (post Ma) driving rejuvenated period rock uplift scenario provides potential explanation for steep channels relief, suggestive rapid erosion rates interior