Date: 16:30-18:30, Friday, November 30, 2018
Place: 3F, Lecture room, Main Chemistry Build.
Speaker: Konstantin Litasov（Novosibirsk State University, Sobolev Institute of Geology and Mineralogy)
講演者：Konstantin Litasov（Novosibirsk State University, Sobolev Institute of Geology and Mineralogy)
Title: Ultrahigh-pressure and super-reduced phases in ophiolite and other rocks: A lesson from synthetic diamond and abrasives
Enigmatic appearance of cuboctahedral diamonds in natural ophiolitic and volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds grown from typical metal solvent requires more attention. We studied several diamond crystals 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 Ib patterns of synthetic diamonds. In the TEM films prepared using focused ion beam technique we find only few metallic inclusions in Tolbachik diamonds. They contains Mn, Ni and minor Si. SRXRF spectra, measured in the range of transitional metals with incident X-ray of 10 keV, confirm these compositions and indicate presence of Fe-Ni and Fe-Ni-Mn inclusions with Cr, Ti, Cu, and Zn impurities. Bulk diamond contains significant amounts of Fe, Ni, Cr and Co in the range of 0-55 ppm. LA-ICP-MS data show significant admixtures of Mn, Fe, Ni and Cu in the same range of concentrations. Most values are comparable with those determined by LA-ICP-MS for similar diamonds from Tibet ophiolites. Mn-Ni (+Fe) solvent was used to produce industrial synthetic diamonds in USSR and Russia with the similar proportions of elements, therefore we concluded that Kamchatka cuboctahedral diamonds are contamination from drilling tools or other hard instruments. However, the way, how they appear in Tolbachik lava, remains unknown. We also carefully considered reference data on inclusions in ophiolitic diamonds and compare them with composition of solvent for industrial diamond synthesis in China and found the same composition close to Ni70Mn25Co5. This cannot be a coincidence and indicates that most diamonds from ophiolite have synthetic nature. In addition brief review of new data on super-reduced phases in ophiolite and other rocks is presented. The published materials indicate that corundum and moissanite from natural rocks are very similar by mineralogy and inclusions with industrially produced materials. Some data clearly indicate that corundum with super-reduced metals, carbide and nitride resemble grains derived from fused alumina used for abrasive tools.