HR: 08:00h
AN: U11D-01 INVITED     [Abstracts]
TI: Tutorial: The EarthScope Investigation of Continental Processes
AU: * Humphreys, E
EM: genehumphreys@gmail.com
AF: Dept. of Geological Sciences, University of Oregon, Eugene, OR 97403 United States
AB: EarthScope is an integrated investigation of continents that uses the U.S. as the study region. Why the U.S.? It is one of the most fruitful subjects for study and it is our country. EarthScope is drilling the San Andreas Fault, geodetically measuring deformation in the tectonically active western U.S., and seismically imaging continental lithosphere across the U.S. The goal is to understand the processes that create and shape continents, and an emphasis on earthquakes and volcanoes recognizes the scientific and social need to understand the underlying physics; these events are the fundamental agents in making continents and they pose genuine risk to society. Making significant progress toward these goals has proven elusive. In response, EarthScope has challenged our community to observe continental structure and earthquake and volcanic cycles on continuous and wide spatial and temporal scales, and to bridge across disciplines to provide an intellectually broad and continuous understanding. As EarthScope begins its study of the western U.S., the following overview provides a framework for consideration; however, we are just on the verge of understanding how this marvelous system works. The western U.S. is one of Earth's major orogenic plateaus. Unlike most regions, deformation is distributed over a broad area. The origins of the distinctive western U.S. tectonic provinces can be traced back to continental rifting 0.5 billion years ago, which created a continental margin upon which tectonic and magmatic activity constructed a coherently heterogeneous land. Aftermaths of the Laramide (Rocky Mountain) event include the current weakness and high elevations of the western U.S. These, combined with applied plate-tectonic loads at the plate margin and a protecting effect of the strong Canadian craton, result in extension of the continental interior (especially the very weak Basin and Range province), shear deformation across the westernmost swath of continent, and contraction in the Pacific Northwest as California moves north. Superimposed on and interacting with all this "plate tectonic" activity is activity driven by vertical flow. The Yellowstone hotspot represents mantle upwelling. Its uplift has focused Basin and Range extension near Yellowstone, and lithosphere is being constructed rapidly. The Columbia River flood basalts (the dominant magmatic initiation of Yellowstone) probably occurred as old dense roots of the Wallowa batholith convectively destabilized and fell into the Earth ("delaminated"), apparently in response to initial Yellowstone upwelling. This delamination was similar to that occurring today beneath the rising southern Sierra Nevada. And lithospheric downwelling beneath southern California draws crust toward the Transverse Ranges.
DE: 8110 Continental tectonics: general (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8178 Tectonics and magmatism
SC: Union [U]
MN: Fall Meeting 2005