俄罗斯科学院物理化学和电化学研究所Andrei Shiryaev研究员学术报告会

地球系统科学论坛第535期：Andrei Shiryaev研究员学术报告会

应304am永利集团官网刘勇胜教授邀请，俄罗斯科学院物理化学和电化学研究所（Institute of Physical Chemistry and Electrochemistry RAS, Moscow, Russia）的Andrei Shiryaev研究员来我校访问并做学术报告。

1） Natural silicon carbide from kimberlites and sediments: polytypes, trace elements, inclusions and speculations on its origin

金伯利岩和沉积物中的天然碳化硅：多型、微量元素和包裹物特征及成因分析

报告时间：2017年6月15日（周四）下午15：00

报告地点：主楼地质斋

报告简介：Natural silicon carbide – moissanite, is known to occur in very diverse geological settings ranging from kimberlites to limestones. Since its formation requires very low fO2values, many of these finds were ascribed to technogenic contamination. However, in the last decade several independent studies reported reliable observations of natural SiC in ophiolites, kimberlites etc. In many cases the moissanite grains contain inclusions of highly reduced phases (native Si, FeSi2etc.). Despite growing number of important papers the process(es) of the moissanite formation remain elusive.

2)Unusualgem-quality Ib diamonds: what can we learn about natural diamond growth?

非常规Ib型宝石级金刚石：对天然金刚石生长的指示

报告时间：2017年6月16日（周五）上午8：30

报告地点：主楼412

报告简介：Natural diamonds with dominating single substitutional nitrogen impurity (type Ib) are rarely encountered, since even moderate annealing at mantle temperatures lead to nitrogen diffusion and formation of more complex defects. I will present results of detailed investigation of unique set of gem quality natural Ib diamonds by complementary techniques – Infra-red microspectroscopy and SIMS.Spatial distribution of point defects, carbon and nitrogen isotopes and of nitrogen concentration were studied. Combined with the data on composition of fluid inclusions the obtained results point to crystallization of the diamonds from oxidized, presumably carbonatitic fluid. It is shown that in the growth direction13C of the diamond becomes systematically lighter for 2-3‰. Simultaneously, we observe substantial decrease of nitrogen concentration and unprecedented progressive enrichment of nitrogen in light isotope, exceeding 30‰. The systematic and substantial changes of the chemical and isotopic composition are explained in the framework of the Burton-Prim-Slichter (BPS) model, which relates partition coefficients of an impurity with the crystal growth rate. It is shown that changes of effective partition coefficients due to gradual decrease of the crystals growth rate describes fairly well the observed scale of the chemical and isotopic variations even during crystal growth in an open system. This model shows that nitrogen isotopic composition of diamond may result from isotopic fractionation during growth and does not reflect isotopic properties of the mantle fluid.

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2017年6月