Tectonic History of Western North America and Southern California - A4

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High quality: http://www.youtube.com/watch?v=Y4hg92mtNyw&fmt;=18 An Animated Tectonic History of Western North America and Southern California. Tanya Atwater, Dept. Geological Sciences, University of California, Santa Barbara, CA Summary list of QuickTime animations: A.Pacific-North America Plate Tectonic History (map views) 1. Pacific Hemisphere, 80 Ma to Present 2. N.E. Pacific and W. North America, 38 Ma to Present 3. California, 20 Ma to Present 4. Southern California, 20 Ma to Present 5. Southern California Paleomagnetic Vectors 6. Southern California, Origin and Dispersal of the Poway Conglomerate B.Geologic History of the Transverse Ranges, Southern California 1. Mesozoic Subduction 2. Miocene: Rifting and rotation, volcanism and deposition in marine basins 3. Plio-Pleistocene: Oblique Shortening against the "Big Bend" 4. Santa Barbara Channel Oil A.3&4. Plate Tectonic History of Southern California, 20 Ma to Present (stable North America held fixed). Drawn and animated by Tanya Atwater using PhotoShop and Morph. Thanks to Craig Nicholson, Bruce Luyendyk, Scott Hornafius, Mark Kammerling, John Crowell, and many others. Images modified after Nicholson, et al, 1995, Geology, v. 22, p. 491; Crouch and Suppe, 1994, Geol. Soc. Amer. Bull., v. 105, p. 1415; Kamerling and Luyendyk, 1985, J. Geophys. Res., v. 90, p. 12485; and Hornafius et al., 1986, Geol. Soc. Amer. Bull., v. 97, p. 1476. Present Situation. At present, the primary Pacific-North American plate boundary runs from Cape Mendocino, along the San Andreas fault system and the Gulf of California spreading centers and transform faults. Notice that the Santa Ynez Mountains, Santa Barbara coast line, Channel Islands, and Santa Monica Mountains all run east-west, crosswise to most other features in the region. Paleomagnetic measurements show that this block, the Western Transverse Ranges Block has been rotated more than ninety degrees. Notice that the continental shelf off southern California and northern Baja California, the California Borderland, is very wide and fragmented. Mid-Cenozoic Situation, 20 Ma. This is a likely reconstruction of the continental rim before it was shifted and reorganized by the evolving plate boundary. The inner Borderland has been collapsed and the Western Transverse Ranges Block has been rotated back in order to place the Channel Islands beside San Diego. The Los Angeles Basin does not yet exist. • Rotation of the Western Transverse Ranges. The Western Transverse Ranges Block started out with its southern rim, the Channel Islands, lying near San Diego. During the extensional shear of the borderland, the block was torn away and rotated out to its present east-west orientation. The gaps that opened up on both sides of the rotating beam are postulated to have been filled from below by core complex-like emplacement of underplated Franciscan materials. • San Andreas System Evolution. As the contact zone between the Pacific and North American plates grew and solidified, the rim of North America fragmented. Pieces were transferred to the Pacific plate, establishing the San Andreas plate boundary inside the continent. • Two stage transfer. The continental transfers occurred in two steps: 1. During the Miocene, coastal California fragments were gradually transferred. 2. Later, about five million years ago, Baja California was transferred as one relatively coherent piece. • Southern California Tectonic Stages. The transfer of Baja California to the Pacific plate profoundly changed the tectonic situation in southern California. Before the Baja transfer, the plate boundary bent outward from the northern San Andreas to the Pacific rim - an oblique-extension configuration, and thus the California borderland was extended and sheared. After the Baja transfer, the plate boundary bent inland into the Gulf, an oblique-compression configuration, and the San Andreas "Big Bend" and the present mountains were created.