By examining the cooling rate of rocks that formed more than 10 miles beneath the Earth's surface, scientists led by The University of Texas at Austin Jackson School of Geosciences have found that water probably penetrates deep into the crust and upper mantle at mid-ocean spreading zones, the places where new crust is made. The finding adds evidence to one side of a long-standing debate on how magma from the Earth's mantle cools to form the lower layers of crust.
Nick Dygert, a postdoctoral fellow in the Jackson School's Department of Geological Sciences, led the research which was published in May in the print edition of Earth and Planetary Science Letters. Collaborators include Peter Kelemen of Colombia University and Yan Liang of Brown University.
The Earth's mantle is a semi-solid layer that separates the planet's crust from the core. Dygert said that while it's well known that magma upwelling from the mantle at mid-ocean spreading zones creates new crust, there are many questions on how the process works.
"There's a debate in the scientific community how oceanic crust forms," Dygert said. "And the different models have very different requirements for cooling regimes."
To learn more about the conditions under which magma turns into crustal rock, Dygert and his collaborators examined rock samples that were part of the Earth's mantle a hundred million years ago, but are now part of a canyon in Oman.
"One can effectively walk down 20 kilometers in the Earth's interior," said Kelemen. "This allows scientists to access rocks that formed far below the seafloor which are not available for study."
The team used "geothermometers" -- the name of a technique that uses mineral compositions inside rock samples to calculate temperatures and reveal the cooling history of the rock. Geothermometers help scientists determine the temperatures experienced by magmas and rocks as they cool, and infer how rapidly the cooling occurred. The study included use of a new geothermometer developed by Liang, which records the maximum temperature a rock attained before it cooled.
"Traditional geothermometers usually give you a cooling temperature rather than a formation temperature for the rock," Dygert said. "This thermometer is a neat new tool because it allows us to look at a part of the cooling history that was inaccessible for igneous rocks previously."
The temperatures recorded in the rocks show that the lower crust and uppermost mantle cooled and solidified almost instantly, Dygert said--like a "hot frying pan being plopped in a sink of water" -- while the deeper mantle cooled more gradually. The temperature change is indicative of water circulating through the crust and uppermost mantle beneath mid-ocean spreading centers, and the heat from deeper portions of the mantle being dissipated through contact with the cooler upper rocks.
Currently, there are two primary theories for crust formation. In the Sheeted Sill hypothesis, circulating seawater cools many small magma deposits at different depths in the lower crust, which would simultaneously cool the upper mantle. In the Gabbro Glacier hypothesis, magma gradually loses heat as it flows away from a central magma chamber.
Dygert said that temperatures recorded by the geothermometers matched with the Sheeted Sill cooling process.
"The Sheeted Sill model requires a very efficient mechanism for cooling because crystallization is happening at all different depths within the crust at the same time," Dygert said. "And what we were able to find strongly implies that hydrothermal circulation was very efficient throughout the crustal section."
Uncovering how crust forms is at the heart of understanding the geological history of our planet, Dygert said, but the results could also have implications for our planet's future. Some scientists have proposed mixing carbon dioxide (CO2) with water and injecting it into mantle rock as a means to fight climate change. The CO2 reacts with minerals in the mantle, which safely locks up the carbon up in their crystal structures. However, Dygert notes that mantle rock that has already been exposed to seawater may not react as readily with CO2, which would slow the carbon capture process. Dygert said that the new results suggest that circulation of water beneath mid-ocean ridges is effectively limited to the crustal section, and that enormous sections of the mantle could be available beneath the oceanic crust to efficiently trap CO2.
The research was supported by the Jackson School of Geosciences, the National Science Foundation, the Alfred P. Sloan Foundation, and an International Continental Drilling Program grant.
Monica Kortsha | EurekAlert!
Water cooling for the Earth's crust
22.11.2017 | Helmholtz Centre for Ocean Research Kiel (GEOMAR)
Retreating permafrost coasts threaten the fragile Arctic environment
22.11.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
22.11.2017 | Business and Finance
22.11.2017 | Physics and Astronomy
22.11.2017 | Physics and Astronomy