Large cylindrical blob of cold material found beneath US West Great Basin

May 27th, 2009 - 1:31 pm ICT by ANI  

Washington, May 27 (ANI): A team of geologists has found a large cylindrical blob of cold material far below the surface of the US West Great Basin.

The Great Basin in the western US is a desert region largely devoid of major surface changes.

The area consists of small mountain ranges separated by valleys and includes most of Nevada, the western half of Utah and portions of other nearby states.

For tens of millions of years, the Great Basin has been undergoing extension - the stretching of Earth’s crust.

While studying the extension of the region, geologist John West of Arizona State University (ASU) was surprised to find that something unusual existed beneath this area’s surface.

West and colleagues found that portions of the lithosphere - the crust and uppermost mantle of the Earth - had sunk into the more fluid upper mantle beneath the Great Basin and formed a large cylindrical blob of cold material far below the surface of central Nevada.

“It was an extremely unexpected finding in a location that showed no corresponding changes in surface topography or volcanic activity,” said West.

West compared his unusual results of the area with tomography models - CAT scans of the inside of Earth - done by geologist Jeff Roth, also of ASU.

West and Roth, both graduate students; working with their advisor, Matthew Fouch, concluded that they had found a lithospheric drip.

“The results provide important insights into fine-scale mantle convection processes, and their possible connections with volcanism and mountain-building on Earth’s surface,” said Greg Anderson, program director in NSF’s Division of Earth Sciences.

A lithospheric drip can be envisioned as honey dripping off a spoon, where an initial lithospheric blob is followed by a long tail of material.

When a small, high-density mass is embedded near the base of the crust and the area is warmed up, the high-density piece will be heavier than the area around it and it will start sinking.

As it drops, material in the lithosphere starts flowing into the newly created conduit.

Seismic images of mantle structure beneath the region provided additional evidence, showing a large cylindrical mass 100 km wide and at least 500 km tall.

“The idea of a lithospheric drip has been used many times over the years to explain things like volcanism, surface uplift, surface subsidence, but you could never really confirm it - and until now, no one has caught a drip in the act, so to speak,” said Fouch. (ANI)

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