Cutaway of the Earth’s surface, down to the liquid core. A numerical convection experiment shows blobs in green, surrounding mantle rock in blue, and former oceanic crust from the surface that has subducted into the interior in yellow. Credit: Dr. Mingming Li/University of Colorado
2 massive blob-like structures lie deep within Earth, roughly on opposite sides of the planet. Each the size of a continent and 100 times taller than Mount Everest, sit on the core, 1,800 miles deep, and about halfway to the center of Earth. Arizona State University scientists suggest these blobs are made of something different from the rest of Earth’s mantle.
“While the origin and composition of the blobs are yet unknown,” said Garnero, “we suspect they hold important clues as to how Earth was formed and how it works today.” The blobs, he says, may also help explain the plumbing that leads to some massive volcanic eruptions, as well as the mechanism of plate tectonics from the convection, or stirring, of the mantle. This is the geo-force that drives earthquakes.
Earth is layered like an onion, with a thin outer crust, a thick viscous mantle, a fluid outer core and a solid inner core. The two blobs sit in the mantle on top of Earth’s core, under the Pacific Ocean on one side and beneath Africa and the Atlantic Ocean on the other. Waves from earthquakes passing through Earth’s deep interior have revealed that these blobs are regions where seismic waves travel slowly. The mantle materials that surround these regions are thought to be composed of cooler rocks, associated with the downward movement of tectonic plates.
The blobs, aka thermochemical piles, have long been depicted as warmer-than-average mantle materials, pushed upward by a slow churning of hot mantle rock. The new paper argues they are also chemically different from the surrounding mantle rock, and may partly contain material pushed down by plate tectonics. They might even be material left over from Earth’s formation, 4.5 billion years ago. The emerging view from seismic and geodynamic information is they appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and have been shaped by the mantle’s large-scale flow. The scientists expect that further work will help clarify the picture and tell of their origin. http://www.newswise.com/articles/giant-blobs-of-rock-deep-inside-the-earth-hold-important-clues-about-our-planet
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2733.html
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