Comparison of enigmatic diamonds from the Tolbachik arc volcano (Kamchatka) and Tibetan ophiolites: Assessing the role of contamination by synthetic materials |
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| Institution: | 1. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia;2. Novosibirsk State University, Novosibirsk, Russia;3. Geochemical Research Center, University of Tokyo, Tokyo, Japan;4. Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia;5. Geodynamic Research Center, Ehime University, Matsuyama, Japan;6. Department of Geosciences, Shizuoka University, Shizuoka, Japan;1. Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany;2. Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, ul. Senacka 1, Kraków 31-002, Poland;3. GeoZentrum Nordbayern, Fachgruppe PaläoUmwelt, Friedrich-Alexander-Universität Erlangen-Nürnberg, Loewenichstraße 28, 91054 Erlangen, Germany;4. Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straße 11, 24118 Kiel, Germany;5. Faculty of Geology, University of Warsaw, Poland;1. Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430205, China;2. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Department of Earth and Environmental Sciences, University of Windsor, Ontario, Canada;4. State Key Lab of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;5. Key Laboratory of Marine Hydrocarbon Resources Environmental Geology, Ministry of Natural Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China;6. Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shandong University of Science and Technology, Qingdao 266590, China;7. School of Earth Sciences, China University of Geosciences Wuhan, Wuhan 430074, China;1. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia;2. Novosibirsk State University, Novosibirsk, Russia;3. Institute for High Pressure Physics RAS, Moscow, Russia;4. Geochemical Research Center, University of Tokyo, Tokyo, Japan;1. Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México, DF, Mexico;2. National Taiwan Normal University, Department of Earth Sciences, 88 Tingzhou Road Section 4, Taipei 11677, Taiwan;3. Department of Geology, St. Mary''s University, Halifax, Nova Scotia, Canada B3H 3C3;4. Department of Energy, Halifax, Nova Scotia B3J 3J9, Canada;1. Department of Research and Cooperation, Mongolian University of Science and Technology, 8th khoroo, Baga toiruu 34, Sukhbaatar district, Ulaanbaatar 14191, Mongolia;2. Department of Earth Sciences and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan;3. Department of Biosphere-Geosphere Science, Faculty of Biosphere-Geosphere Science, Okayama University of Science, 1-1 Ridaicho, Kita-ku, Okayama-shi 700-0005, Japan;4. Department of Chemistry, Gakushuin University, 1-5-1, Mejiro, Toshima-ku, Tokyo 171-8588, Japan;5. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550, Japan |
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| Abstract: | The enigmatic appearance of cuboctahedral diamonds in ophiolitic and arc volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds that were grown from metal solvent requires a critical reappraisal. We have studied 15 diamond crystals and fragments from Tolbachik volcano lava flows, using Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), synchrotron X-ray fluorescence (SRXRF) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS). FTIR spectra of Tolbachik diamonds correspond to typical type Ib patterns of synthetic diamonds. In TEM films prepared using focused ion beam technique, we find Mn-Ni and Mn-Si inclusions in Tolbachik diamonds. SRXRF spectra indicate the presence of Fe-Ni and Fe-Ni-Mn inclusions with Cr, Ti, Cu, and Zn impurities. LA-ICP-MS data show variable but significantly elevated concentrations of Mn, Fe, Ni, and Cu reaching up to 70 ppm. These transition metal concentration levels are comparable with those determined by LA-ICP-MS for similar diamonds from Tibetan ophiolites. Mn-Ni (+Fe) solvent was widely used to produce industrial synthetic diamonds in the former USSR and Russia with very similar proportions of these metals. Hence, it appears highly probable that the cuboctahedral diamonds recovered from Kamchatka arc volcanic rocks represent contamination and are likely derived from drilling tools or other hard instruments. Kinetic data on diamond dissolution in basaltic magma or in fluid phase demonstrate that diamond does not form under the pressures and temperature conditions prevalent within the magmatic system beneath the modern-day Klyuchevskoy group of arc volcanoes. We also considered reference data for inclusions in ophiolitic diamonds and compared them with the composition of solvent used in industrial diamond synthesis in China. The similar inclusion chemistry close to Ni70Mn25Co5 for ophiolitic and synthetic Chinese diamonds scrutinized here suggests that most diamonds recovered from Tibetan and other ophiolites are not natural but instead have a synthetic origin. In order to mitigate further dubious reports of diamonds from unconventional tectonic settings and source rocks, we propose a set of discrimination criteria to better distinguish natural cuboctahedral diamonds from those produced synthetically in industrial environments and found as contaminants in mantle- and crust-derived rocks. |
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