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

More articles from Earth Sciences:

nachricht Clear as mud: Desiccation cracks help reveal the shape of water on Mars
20.04.2018 | Geological Society of America

nachricht Hurricane Harvey: Dutch-Texan research shows most fatalities occurred outside flood zones
19.04.2018 | European Geosciences Union

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Scientists re-create brain neurons to study obesity and personalize treatment

20.04.2018 | Health and Medicine

Spider silk key to new bone-fixing composite

20.04.2018 | Materials Sciences

Clear as mud: Desiccation cracks help reveal the shape of water on Mars

20.04.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>