One great beauty of plate tectonics theory is that it explains so many geological phenomena at one time. But plate tectonics could not explain the location of many volcanic islands – Hawaii, the Azores or the Galapagos Islands, often called “hotspots” – far from the edge of tectonic plates. To deal with those observations, geologists invoked the concept of “plumes” – areas where buoyant sections of mantle material rose, melted and developed into concentrated upwellings of magma, forming seamounts and island chains.
A running battle has evolved over the last 30 years concerning hotspots: One camp claims it is not necessary to invoke mantle plumes to explain such volcanic islands, and the other camp – a sizeable portion of the geological community – supports mantle plumes as the most internally consistent explanation for a wide variety of data.
A study published this week in the journal Nature raises the bar for plume opponents by finding a close correlation between modeled and observed ratios of uranium-series isotopes across eight island locations. The study strongly supports upwelling of mantle material as the source of these islands. Moreover, the detailed data allow researchers to estimate the change in temperature, speed and size of mantle plumes at the locations studied.
Alberto Saal, assistant professor of geology at Brown University, contributed data from the Galapagos Islands, complementing information from researchers working in Hawaii, Pitcairn, the Azores, the Canary Islands, the Afar region and Iceland. With such a breadth of data in hand, lead author Bernard Bourdon, professor at the Swiss Federal Institute of Technology in Zürich (formerly at the Institut de Physique du Globe in Paris), was able to build robust correlations between the ratios of isotopes in the actinide series and the flux of material needed to build the observed islands.
“What’s exciting about this,” says Saal, “is that it allows us to make inferences about physical conditions based on chemical measurements.” While it is impossible to visit the boundary of the mantle to make the physical measurements, it is possible to collect the chemical evidence that has been brought all the way to the surface.
When mantle rocks melt, the ratio of uranium isotopes to their decay products changes dramatically, then moves back to equilibrium at a steady, predictable rate. Using this change in ratios, the researchers were able to determine how quickly and completely the material melted. This also allowed them to estimate the difference in temperature between the mantle and the plumes, which determines the speed and size of the upwellings.
Beyond adding to the general evidence for mantle plumes, the study allows researchers to generate some numbers that could potentially be tested. “We think we can provide some extra constraints on these parameters that are generally poorly known,” says Bourdon.
Their estimates of temperature differences ranged between 50 and 200 degrees C with the larger differences seen in areas believed to have stronger plumes – such as Hawaii and the Galapagos. Assuming symmetrical plumes, Bourdon and his colleagues were also able to make estimates of the radius of mantle plumes at each location that roughly fit with estimates of plume diameters from seismological sources.
The more researchers can make the notion of hotspots concrete, the better chance they have to prove it right – or wrong.
Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.
Martha Downs | EurekAlert!
Strength of tectonic plates may explain shape of the Tibetan Plateau, study finds
25.07.2017 | University of Illinois at Urbana-Champaign
NASA flights gauge summer sea ice melt in the Arctic
25.07.2017 | NASA/Goddard Space Flight Center
Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers
Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...
Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.
At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...
3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects
A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
21.07.2017 | Event News
19.07.2017 | Event News
12.07.2017 | Event News
25.07.2017 | Physics and Astronomy
25.07.2017 | Earth Sciences
25.07.2017 | Life Sciences