Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


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


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:

More articles from Earth Sciences:

nachricht UCI and NASA document accelerated glacier melting in West Antarctica
26.10.2016 | University of California - Irvine

nachricht Ice shelf vibrations cause unusual waves in Antarctic atmosphere
25.10.2016 | American Geophysical 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: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Greater Range and Longer Lifetime

26.10.2016 | Power and Electrical Engineering

VDI presents International Bionic Award of the Schauenburg Foundation

26.10.2016 | Awards Funding

3-D-printed magnets

26.10.2016 | Power and Electrical Engineering

More VideoLinks >>>