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Geology in the news: They've recovered a fragment of the Russian Chelyabinsk meteorite from a local lake, which weighed over 570 kg, one of the largest meteorite fragments ever found. (It broke their scale!) See http://rt.com/news/largest-fragment-meteorite-lifted-258/ . Plate Tectonics, Part IV (What might the FUTURE hold in store?) Another possible scenario ... The BASIN AND RANGE Province of the western U.S., including all of Nevada and parts of surrounding states, MAY be an area where North America is trying to split apart! You've already been introduced to the geology of this area ..... ... the result of accreted terranes and ancient subduction zones, now fractured into multiple slivers. How? Why? The mantle upwelling beneath the East Pacific Rise doesn't just cease to exist in between the Gulf of California and the Gorda Ridge. Shallow subduction of the Farallon Plate is believed to also be a major factor. (The Juan de Fuca Plate and Gorda Plate are small remnants of the Farallon Plate.) This region has been broadly UPLIFTED by tectonic forces pushing up from beneath. The plains of Wyoming are very flat, but 7000-8000 feet (2100 to 2400 m) above sea level. The Grand Canyon catches the eye for its tremendous depth, but the North Rim is also over 8000 feet (2400 m) above sea level! Note how FLAT that upland surface is! In most other areas, the rocks have fractured in normal faults, which are produced only by stretching a brittle material - pulling it apart. On a larger scale, this then shows up in repeated patterns of block faulting CRUST A. uplift occurs B. Tensional stresses are set up C. Shallow, brittle rocks fracture - all go up, but some blocks go up more than others. D. Erosion of horsts (high blocks) fills in grabens (low valleys). This produces a series of downdropped blocks called GRABENS in between the uplifted HORSTS. (The grabens are the valleys, the mountain ranges the horsts.) The Humboldt Range of Nevada, for example, is part of this system. Sierra Nevada White Mtns. of California Silver Peak Range of Nevada Owens Valley The Sierra Nevada marks the western margin of the Basin and Range. Owens Valley, between the Sierra (left) and White Mountains (right) is a typical graben. Direction of view in previous slide This is what has produced this pattern in the geologic maps. Reno Salt Lake City The distance from modern Reno, NV and Salt Lake City, Utah, has increased by some 30 miles (50 km) in this process. What COULD happen as an alternative scenario, as a result of this process in the western U.S.? It's thinking about scenarios like this that has led some geologists to call geophysics "The realm of conjecture, speculation and dreams." Coming NEXT: the origin of the Universe!