Gooey rock in mantle thickens 1,000 kilometers down | Science News

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Gooey rock in mantle thickens 1,000 kilometers down

Transition region resists the movement of magma plumes, sinking plates

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2:00pm, December 10, 2015
mantle upflow

HOT STUFF  Earth’s mantle rapidly becomes more viscous around 1,000 kilometers below ground (gray bar), new research shows. That viscosity increase could narrow and deflect the rising plumes of hot rock (yellow blobs) that fuel volcanoes on the surface.

A sixth of the way to the center of the Earth, things get goopy. Using variations in the planet’s gravitational tug, geophysicists have discovered that the viscosity of Earth’s mantle rapidly increases about 1,000 kilometers below ground.

The increasingly viscous rock acts like geologic molasses, slowing down anything trying to push through it. That includes sinking tectonic plates and the rising plumes of hot rock that fuel volcanoes, geophysicist Maxwell Rudolph of Portland State University in Oregon and colleagues  report in the Dec. 11 Science. While the origins of the viscosity increase remain unknown, its discovery should help geologists better understand the flow of heat and rock through the planet’s interior.

The depth of the viscosity jump may even be a more suitable dividing line between the upper and lower mantle than the 660-kilometer-deep region

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