Tillamook Volcanic Series: Further evidence for tectonic rotation of the Oregon Coast Range

摘要: Paleomagnetic directions from the Eocene Tillamook Volcanic Series of Oregon Coast Range point 46 o clockwise expected field direction. Potassium argon dating six dikes and flows this formation yields a mean age 44.3 + 0.6 m.y. These results establish that coastal block Simpson Cox (1977) extends north to Oregon-Washington border has rotated 13 during past 44 The undergone no detectable north-south translation. A two phase model is developed explain tectonic history anomalous magnetic Pacific northwest region. Phase I rotation, active between 50 42 m.y.B.P., fragmentation Farallon plate with rotation fragment its accretion North America. II 20 m.y.b.p. present, occurs in association extension Basin province.