Interpreting Quaternary uplift rates at the Mendocino triple junction, northern California, from uplifted marine terraces

Abstract

Analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3-81 ka, and temporal changes in uplift rates from <1 m/ka to 3-5 m/ka that may reflect response to changes in tectonic regime during passage of the Mendocino triple junction (MTJ). A possible mechanism for regional uplift is growth of a slab window south of the MTJ. The region of most rapid uplift is 25-43 km south of the MTJ, immediately south of the northern boundary of the slab window. The coastline is tilted upward to the south in the region directly above the southern edge of the subducted Gorda plate. At Point Delgada, 55 km south of the present MTJ, where the northern edge of the slab window passes {approximately}300 ka, uplift rates have been 1.2 m/ka for at least 330 ka. More than 1.4 m.y. after passage of the southern edge of the subducted slab, at the Mendocino coast, uplift rates have been less than 0.4 m/ka for at least 330 ka.