Mesmerising geochemistry on a micrometre scale

The secrets of how rocks form are often hidden from the naked eye and require sophisticated analytical instruments to be deciphered by curious scientists. School of Geography, Geology and the Environment petrologists Dr Ralf Halama and Dr Ralf Gertisser are studying enigmatic rocks from a volcano in Armenia, which are referred to as xeno-pumice due to their high vesicularity and their distinct white colour in the dark basaltic scoria, to throw a light on their mysterious origin. The quest for understanding the origin of such xeno-pumice gained momentum during a submarine volcanic eruption off the island of El Hierro (Canary Islands) in 2011, which produced similar rocks. Their origin is highly debated and hypotheses include processes as diverse as representing juvenile magma, remelted magmatic material and xenoliths from sedimentary layers that partially melted and vesiculated.

Thanks to funding from the School of Geography, Geology and the Environment, Dr Halama was able to investigate the Armenian rocks using an electron microprobe at Kiel University (Germany). The electron microprobe allows geochemical analyses of material on a scale of a few micrometers, and the chemical characterisation of the phases present provides key information regarding the origin of these rocks. Additional Sr-Nd isotopic data will be obtained in co-operation with Dr Ivan Savov (Leeds University) and Dr Khachatur Meliksetian (Armenian Academy of Sciences) to gain further insights into how these rocks formed.

Relevant publications:

Sugden, P.J., Savov, I.P., Wilson, M., Meliksetian, K., Navasardyan, G. and Halama, R., 2019: The thickness of the mantle lithosphere and collision-related volcanism in the Lesser Caucasus. Journal of Petrology 60, 199-230. DOI:10.1093/petrology/egy111.

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