地球系统科学论坛第463期：Vincent SOUSTELLE报告会

试点学院改革-学术报告制：第六十八讲

报告题目：Deformation of olivine-orthopyroxene aggregates at HP-HT: Implication for the seismic properties of the asthenosphere

报 告 人：Vincent SOUSTELLE

报告时间：6月30日（周四）下午3:00

报告地点：主楼412

报告人简介：

Vincent SOUSTELLE studied at the University of Montpellier 2 (France) where he obtained a PhD in 2010. From 2011 to 2014 Vincent SOUSTELLE was post-doc at the Bayerisches Geoinstitut (BGI) in Bayreuth (Germany) with 2 years spent as an Alexander von Humboldt fellow. Vincent SOUSTELLE did a second post-doc at Brown University (USA) at the Department of Earth, Environment and Planetary Sciences. Vincent SOUSTELLE is now a professor for the School of Earth Sciences at the China University of Geosciences, Wuhan. His research focuses on mantle deformation and rheology. He is investigating through natural observations and laboratory experiments how microstructures of the mantles minerals microstructures are evolving under different conditions of deformation and what is the implications for the seismic properties of the mantle. Recently, he particularly focused my studies on the interaction between melt-rock reaction and deformation to investigate the effect of deformation on melt-migration and extraction as well as how the presence of melt or secondary phases affect the deformation mechanisms.

报告内容简介：In this talk, after introducing some basics on mantle seismic anisotropy and the factor controlling the olivine crystal preferred orientation (CPO), I will report a series of deformation experiments on olivine-orthopyroxene aggregates investigating the effect of pressure, temperature and composition on the development of mineral crystal preferred orientations (CPO) and seismic properties of the asthenosphere. The seismic anisotropy in the mantle is usually ascribed to the development of olivine CPO due to its deformation in the dislocation creep regime. Other phases, such as orthopyroxene, are assumed to only dilute the intensity of the anisotropy. Recent deformation experiments demonstrate that the contribution of diffusion creep may be stronger than dislocation creep for olivine-pyroxene aggregates and that the resulting CPO can vary from an olivine aggregate deformed in dislocation creep. These studies were however carried out at pressures lower than those of the asthenosphere. These experiments fill this gap by investigating the deformation of olivine-orthopyroxene aggregates at pressures corresponding to depths of about 100 to 250 km (~ 3 to 8 GPa). State-of-the-art microstructural analyses demonstrate that diffusion accommodated grain boundary sliding (difGBS) are necessary to explain the olivine CPO observed at 3 GPa. Above 3 GPa, the relative contribution of difGBS and the mechanisms related to the motion of dislocations is controlled by the amount of secondary phases. The occurrence of such mechanisms are supported by the consistency between the seismic properties, in particular Vsh/Vsv, and the global seismic observations on the asthenosphere from intraplate settings and mid-oceanic ridges.

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2016年6月28日