Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Seismologists detect a sunken slab of ocean floor deep in the Earth

18.05.2006


Halfway to the center of the Earth, at the boundary between the core and the mantle, lies a massive folded slab of rock that once formed the ocean floor and sank beneath North America some 50 million years ago. A team of seismologists led by scientists at the University of California, Santa Cruz, detected the slab by analyzing seismic waves reflected from the deepest layer of the mantle beneath an area off the west coast of Central America.



"If you imagine cold honey pouring onto a plate, you would see ripples and folds as it piles up and spreads out, and that’s what we think we are seeing at the base of the mantle," said Alex Hutko, a graduate student in Earth sciences at UCSC and first author of a paper describing the new findings in the May 18 issue of the journal Nature.

The discovery sheds new light on the processes that drive the movement of Earth’s tectonic plates. The planet’s outermost layer, or lithosphere, is broken into large, rigid plates composed of the crust and the outer layer of the mantle. New plate material is created at mid-oceanic ridges, where the ocean floor spreads apart, and old plate material is consumed in subduction zones, where one plate dives beneath another. But the fate of subducted lithosphere has been uncertain.


"There is a big debate over whether subducted slabs sink all the way down to the base of the mantle or get trapped in the upper mantle. This is one line of evidence favoring the presence of subducted slabs in the deep mantle," said Thorne Lay, professor of Earth sciences at UCSC and coauthor of the Nature paper.

"It’s the first evidence from direct imaging to support the idea that ancient seafloor makes its way down to the bottom of the mantle," Hutko added.

Within the mantle, which extends to a depth of about 1,740 miles, cold rock sinks while hot plumes rise toward the surface, and this slow circulation of mantle rock is thought to drive the movement of plates in the lithosphere. The base of the mantle absorbs heat from the core. The researchers were able to image the buckling and folding of subducted oceanic lithosphere at the base of the mantle because of the temperature difference between the relatively cool subducted slab and the hotter mantle rock surrounding it.

The subducted slab is composed of essentially the same minerals as the surrounding mantle, but its temperature is about 700 degrees Celsius cooler, Hutko said. This temperature difference affects the location of a "phase transition," where the crystal structure of the mantle rock changes due to increasing pressure and temperature with depth. Seismic energy reflected by this phase transition revealed an abrupt step in the phase boundary about 60 miles (100 kilometers) high.

"That’s more than the thickness of the crust," Lay said. "It’s a huge geological structure and it requires some large-scale dynamic process to produce it. A subducted slab piling up and spreading out is the only mechanism we know of that could give such an abrupt step."

The researchers also saw evidence of hot plume-like structures at the edge of the slab, indicating possible upwelling of hot material from the base of the mantle as the spreading slab pushes into it.

"We think there is a kind of pushing and bulldozing away of a hot basal layer of the mantle, giving rise to small plumes at the edges," Hutko said.

The study used seismic data from earthquakes in South America that were recorded at seismographic stations in the western United States. The researchers analyzed the data using imaging techniques adapted from those used in oil exploration to study complex structures in the crust.

"The oil industry has been using these techniques for decades, but only recently have we been able to exploit them for the deep Earth because of new data available from the seismographic network," Hutko said.

Tim Stephens | EurekAlert!
Further information:
http://www.ucsc.edu

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Gold shines through properties of nano biosensors

17.08.2017 | Physics and Astronomy

Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter

17.08.2017 | Earth Sciences

Mars 2020 mission to use smart methods to seek signs of past life

17.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>