Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Volcanic arcs form by deep melting of rock mixtures

10.04.2017

Study changes our understanding of processes inside subduction zones

Beneath the ocean, massive tectonic plates collide and grind against one another, which drives one below the other. This powerful collision, called subduction, is responsible for forming volcanic arcs that are home to some of Earth's most dramatic geological events, such as explosive volcanic eruptions and mega earthquakes.


It was long-thought that fluids from a subducted tectonic plate and melted sediments percolated into the mantle where they mixed, triggering more melting, and eventually erupt at the surface (left). Mixing and melting are reversed in the mélange model (right).

Credit: Jack Cook, Woods Hole Oceanographic Institution

A new study published in the journal Science Advances changes our understanding of how volcanic arc lavas are formed, and may have implications for the study of earthquakes and the risks of volcanic eruption.

Researchers led by the Woods Hole Oceanographic Institution (WHOI) have discovered a previously unknown process involving the melting of intensely-mixed metamorphic rocks--known as mélange rocks--that form through high stress during subduction at the slab-mantle boundary.

Until now, it was long-thought that lava formation began with a combination of fluids from a subducted tectonic plate, or slab, and melted sediments that would then percolate into the mantle. Once in the mantle, they would mix and trigger more melting, and eventually erupt at the surface.

"Our study clearly shows that the prevailing fluid/sediment melt model cannot be correct," says Sune Nielsen, a WHOI geologist and lead author of the paper. "This is significant because nearly all interpretations of geochemical and geophysical data on subduction zones for the past two decades are based on that model."

Instead, what Nielsen and his colleague found was that mélange is actually already present at the top of the slab before mixing with the mantle takes place.

"This study shows--for the first time--that mélange melting is the main driver of how the slab and mantle interact," says Nielsen.

This is an important distinction because scientists use measurements of isotope and trace elements to determine compositions of arc lavas and better understand this critical region of subduction zones. When and where the mixing, melting, and redistribution of trace elements occurs generates vastly different isotopic signature ratios.

The study builds on a previous paper by Nielsen's colleague and co-author Horst Marschall of Goethe University in Frankfurt, Germany. Based on field observations of mélange outcrops, Marschall noted that blobs of low-density mélange material, called diapirs, might rise slowly from the surface of the subducting slab and carry the well-mixed materials into the mantle beneath arc volcanoes.

"The mélange-diapir model was inspired by computer models and by detailed field work in various parts of the world where rocks that come from the deep slab-mantle interface have been brought to the surface by tectonic forces," Marschall says. "We have been discussing the model for at least five years now, but many scientists thought the mélange rocks played no role in the generation of magmas. They dismissed the model as 'geo-fantasy.'"

In their new work, Nielsen and Marschall compared mixing ratios from both models with chemical and isotopic data from published studies of eight globally representative volcanic arcs: Marianas, Tonga, Lesser Antilles, Aleutians, Ryukyu, Scotia, Kurile, and Sunda.

"Our broad-scale analysis shows that the mélange mixing model fits the literature data almost perfectly in every arc worldwide, while the prevailing sediment melt/fluid mixing lines plot far from the actual data," Nielsen says.

Understanding the processes that occur at subduction zones is important for many reasons. Often referred to as the planet's engine, subduction zones are the main areas where water and carbon dioxide contained within old seafloor are recycled back into the deep Earth, playing critical roles in the control of long-term climate and the evolution of the planet's heat budget.

These complex processes occur on scales of tens to thousands of kilometers over months to hundreds of millions of years, but can generate catastrophic earthquakes and deadly tsunamis that can occur in seconds.

"A large fraction of Earth's volcanic and earthquake hazards are associated with subduction zones, and some of those zones are located near where hundreds of millions of people live, such as in Indonesia," Nielsen says. "Understanding the reasons for why and where earthquakes occur, depends on knowing or understanding what type of material is actually present down there and what processes take place."

The research team says the study's findings call for a reevaluation of previously published data and a revision of concepts relating to subduction zone processes. Because mélange rocks have largely been ignored, there is almost nothing known about their physical properties or the range of temperatures and pressures they melt at. Future studies to quantify these parameters stand to provide even greater insight into the role of mélange in subduction zones and the control it exerts over earthquake generation and subduction zone volcanism.

###

This work was funded by a grant from the National Science Foundation Division of Earth Sciences.

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. For more information, please visit http://www.whoi.edu.

Media Contact

WHOI Media Office
media@whoi.edu
508-289-3340

 @WHOImedia

http://www.whoi.edu 

WHOI Media Office | EurekAlert!

More articles from Earth Sciences:

nachricht Massive organism is crashing on our watch
18.10.2018 | S.J. & Jessie E. Quinney College of Natural Resources, Utah State University

nachricht Arctic sea ice decline driving ocean phytoplankton farther north
16.10.2018 | 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: Goodbye, silicon? On the way to new electronic materials with metal-organic networks

Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) together with scientists from Dresden, Leipzig, Sofia (Bulgaria) and Madrid (Spain) have now developed and characterized a novel, metal-organic material which displays electrical properties mimicking those of highly crystalline silicon. The material which can easily be fabricated at room temperature could serve as a replacement for expensive conventional inorganic materials used in optoelectronics.

Silicon, a so called semiconductor, is currently widely employed for the development of components such as solar cells, LEDs or computer chips. High purity...

Im Focus: Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles

Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...

Im Focus: Disrupting crystalline order to restore superfluidity

When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.

We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...

Im Focus: Micro energy harvesters for the Internet of Things

Fraunhofer IWS Dresden scientists print electronic layers with polymer ink

Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...

Im Focus: Dynamik einzelner Proteine

Neue Messmethode erlaubt es Forschenden, die Bewegung von Molekülen lange und genau zu verfolgen

Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Conference to pave the way for new therapies

17.10.2018 | Event News

Berlin5GWeek: Private industrial networks and temporary 5G connectivity islands

16.10.2018 | Event News

5th International Conference on Cellular Materials (CellMAT), Scientific Programme online

02.10.2018 | Event News

 
Latest News

RUDN chemist tested a new nanocatalyst for obtaining hydrogen

18.10.2018 | Life Sciences

Massive organism is crashing on our watch

18.10.2018 | Earth Sciences

Electrical enhancement: Engineers speed up electrons in semiconductors

18.10.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>