报告题目：How deep and hot is a diamond?

各位老师和同学：
应徐义刚院士邀请，意大利帕多瓦大学（University of Padova）地球科学院Paolo Nimis教授近期将访问我所，并将于本周三上午做“同位素室学术报告”2018年第12次报告。欢迎大家参加并积极参与讨论！

报告题目：How deep and hot is a diamond?
报 告 人：Prof. Paolo Nimis (University of Padova, Italy)
报告时间：4月11日（周三）上午10:30
报告地点：综合楼702会议室

报告人简介：
Professor Paolo NIMIS is the expert of Mineralogy and Metallogeny. He has a wide range of interest in research, including: 1) Crystal-chemistry of pyroxenes and relations between crystal-chemical properties and formation conditions; 2) Thermobarometry of mafic and ultramafic rocks and diamond inclusions, geochemistry of mantle rocks, and their relationships with the diamond-potential of kimberlites; 3) Mafic-ultramafic-hosted VMS deposits, their geodynamic setting and comparison with present-day seafloor mineralizations; 4) Alpine copper metallogenesis and provenancing. He has published more than 80 SCI papers.
报告摘要：
A good understanding of the distribution of diamond in Earth’s mantle provides constraints for the evaluation of diamond potential of economic targets and for the assessment of the deep carbon cycle in ancient Earth. Much of what we know about the depth distribution of diamond is derived from the study of rare mineral inclusions that are amenable to conventional two-phase thermobarometry. However, non-touching inclusions were not necessarily in equilibrium at their encapsulation time, whereas touching inclusions could reequilibrate after entrapment. Moreover, since diamonds can form under a wide range of redox conditions, the unknown Fe3+/Fetot ratios in the inclusions may lead to large uncertainties on T estimates based on Fe–Mg exchange thermometry and, in turn, on P estimates. The development of single-mineral thermobarometers applicable to isolated inclusions has in part overcome the equilibrium issue. However, as yet only chromian clinopyroxene allows to estimate both P and T with a precision comparable, if appropriate analytical conditions are used, to that of conventional methods. In fact, no effective barometers exist for some of the most abundant inclusion types, such as olivine and the eclogitic minerals. An additional problem is whether the inclusions are syngenetic with diamond or they represent passively captured pre-existing material. In the latter case, incomplete chemical resetting during rapid diamond growth may prevent determination of the conditions of diamond formation.
Recent studies suggest that the imposition of diamond morphology on the inclusion (the most widely used criterion for syngenesis) is not unique to syngenetic inclusions, casting doubts on the real significance of P-T data extracted from many reported “syngenetic” inclusions in diamonds. The determination of the remnant P on the inclusion, e.g., using data from X-ray diffractometry, birefringence analysis or Raman spectroscopy, provides an alternative way to diamond barometry using elasticity theory. Application of this methodology is still at its infancy, because of uncertainties in the thermoelastic behaviour of the minerals, potential non-elastic relaxation and technical limitations. It is a field of on-going development, which may eventually allow evaluation of the depth of provenance of diamonds containing minerals that are chemically insensitive to P, such as the abundant upper-mantle olivine or the super-deep ferropericlase. Although available data suggest that lithospheric diamonds may come from any depth below the graphite–diamond transition, owing to the above limitations recognition of subtle inhomogeneity in the vertical distribution of diamond (or of specific diamond populations) remains challenging. Further development of conventional and non-conventional thermobarometric methods may allow us to increase the statistical significance of the diamond P-T record and may eventually contribute to refine models of diamond formation in the sub-cratonic mantle.