ALBERT

Description: The ultimate origin of water in the Earth's hydrosphere is in the deep Earth--the mantle. Theory and experiments have shown that although the water storage capacity of olivine-dominated shallow mantle is limited, the Earth's transition zone, at depths between 410 and 660 kilometres, could be a major repository for water, owing to the ability of the higher-pressure polymorphs of olivine--wadsleyite and ringwoodite--to host enough water to comprise up to around 2.5 per cent of their weight. A hydrous transition zone may have a key role in terrestrial magmatism and plate tectonics, yet despite experimental demonstration of the water-bearing capacity of these phases, geophysical probes such as electrical conductivity have provided conflicting results, and the issue of whether the transition zone contains abundant water remains highly controversial. Here we report X-ray diffraction, Raman and infrared spectroscopic data that provide, to our knowledge, the first evidence for the terrestrial occurrence of any higher-pressure polymorph of olivine: we find ringwoodite included in a diamond from Juina, Brazil. The water-rich nature of this inclusion, indicated by infrared absorption, along with the preservation of the ringwoodite, is direct evidence that, at least locally, the transition zone is hydrous, to about 1 weight per cent. The finding also indicates that some kimberlites must have their primary sources in this deep mantle region.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pearson, D G -- Brenker, F E -- Nestola, F -- McNeill, J -- Nasdala, L -- Hutchison, M T -- Matveev, S -- Mather, K -- Silversmit, G -- Schmitz, S -- Vekemans, B -- Vincze, L -- England -- Nature. 2014 Mar 13;507(7491):221-4. doi: 10.1038/nature13080.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, Alberta T6G 2E3, Canada. ; Geoscience Institute - Mineralogy, Goethe University, Altenhoferallee 1, 60438 Frankfurt, Germany. ; Dipartimento di Geoscienze, Universita di Padova, 35137 Padua, Italy. ; Department of Earth Sciences, Durham University, Durham DH1 3LE, UK. ; Institut fur Mineralogie und Kristallographie, Universitat Wien, Althanstrasse 14, 1090 Wien, Austria. ; Trigon GeoServices Ltd, 2780 South Jones Boulevard, #35-15, Las Vegas, Nevada 89146, USA. ; Department of Analytical Chemistry, Ghent University, Krijgslaan 281 S12, B-9000 Ghent, Belgium.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24622201" target="_blank"〉PubMed〈/a〉