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Immiscibility in magmas, like oil and water
A research team from the universities of Cambridge and Liège, with the participation of industry stakeholders, has just identified an important and furtive mechanism that occurs during the cooling of basalts, the most abundant type of magmatic rock on Earth and which could be the source of important ore deposits. This discovery is published in the journal Nature Communications.
agmas produced in the Earth's mantle contribute to the construction of the crust as they erupt on the surface of our planet. When these magmas cool, they crystallize and produce a sequence of rocks with different characteristics and compositions. This "differentiation" process is responsible for the diversity of magmatic rocks that we see today in volcanic regions.
has been studying for many years the process of immiscibility in magmas, with a particular interest in its implication for the formation of metal deposits. Immiscibility refers to the inability of two liquids to mix, such as oil and water. In magmas, this immiscibility develops during cooling when the melt suddenly separates into two magmas of different compositions. The researchers are convinced that this process can be at the origin of different types of ores.
Electron microscope image (backscattered electron) of an immiscible basalt from Yellowstone province, USA.
To verify this theory, researchers from the University of Liège collaborated with the University of Cambridge. Victoria Honour, a young researcher at the Cambridge Department of Earth Sciences, came to Liège to gain access to the new experimental equipment at the ULiège Experimental Petrology Laboratory. Together, the researchers were able to study immiscibility processes in magmas using natural rock samples from around the world and through experiments in high-temperature furnaces combined with high-resolution imaging and electron probe microanalysis.
One of the major discoveries of this study is the characterization of a nano-emulsion of two liquids using atomic probe tomography on magmatic glass, thus redefining the physical nature of magmas. The measurements, performed at CAMECA Instruments Inc. (Madison, USA), determined the chemical composition of globules at the nanometer scale. These new high-resolution analytical techniques have led the team to develop an understanding of processes that have not been revealed by conventional optical and analytical approaches, although these rocks have been studied for decades.
The discovery of the immiscibility process in basalts has important implications for the physical properties of magmas, especially important for eruption mechanisms.
Honour VC, Holness MB, Charlier B, Piazolo SC, Namur O, Prosa TJ, Martin I, Helz RT, Maclennan J, Jean MM (2019) Compositional boundary layers trigger liquid unmixing in a basaltic crystal mush. Nature Communications 10(1) : 4821
Honour VC, Holness MB, Partridge JL, Charlier B (2019) Microstructural evolution of silicate immiscible liquids in ferrobasalts. Contributions to Mineralogy and Petrology 174(9) : 77
Bernard CHARLIER I UR Geology I Laboratoire de pétrologie sédimentaire