Tuesday, March 19, 2013

'Lost' tectonic plate found beneath California


by Stephanie Pappas - LiveScience

A tectonic plate that disappeared under North America millions of years ago still peeks out in central California and Mexico, new research finds.
The Farallon oceanic plate was once nestled between the Pacific and North American plates, which were converging around 200 million years ago at what would become the San Andreas fault along the Pacific coast. This slow geological movement forced the Farallon plate under North America, a process called subduction.
Much of the Farallon plate got pushed down into the mantle, the gooey molten layer below the Earth's crust. Off the coast, parts of the plate fragmented, leaving some remnants at the surface, stuck to the Pacific plate.
Now, new research published Monday, March 18, in the journal Proceedings of the National Academy of Sciences, finds that these pieces of Farallon plate are attached to much larger chunks at the surface. In fact, part of the Baja region of Mexico and part of central California near the Sierra Nevada mountains sit upon slabs of Farallon plate.
The finding solves a mystery of California geology. Earth scientists use seismic waves (either recorded from earthquakes or created with dynamic charges or other methods) to map out the region beneath the Earth's surface. Softer and hotter materials slow seismic waves down. Read More