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!
Clear as mud: Desiccation cracks help reveal the shape of water on Mars
20.04.2018 | Geological Society of America
Hurricane Harvey: Dutch-Texan research shows most fatalities occurred outside flood zones
19.04.2018 | European Geosciences Union
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.
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...
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...
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...
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...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Health and Medicine
20.04.2018 | Materials Sciences
20.04.2018 | Earth Sciences