Renewal: Petrology and Geochemistry of the Deep Lower Mantle

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项目编号	1447438
	Renewal: Petrology and Geochemistry of the Deep Lower Mantle
	Ho-kwang Mao
主持机构	Carnegie Institution of Washington
项目开始年	2015
	2015-04-15
项目结束日期	2018-03-31
资助机构	US-NSF
项目类别	Continuing grant
项目经费	246033(USD)
国家	美国
语种	英语
英文摘要	Stretching from 670 kilometers depth below the Earth's surface to the core-mantle boundary at 2,900 kilometers depth, the lower mantle comprises more than half of our planet by volume. Information on its chemical composition and petrological constituents is crucial for understanding the solid Earth, but is very scarce, especially for the inaccessible deep lower mantle (DLM) underneath 1800 kilometers. The extremely high pressure and temperature conditions of the DLM make it very difficult to simulate and investigate in the laboratory, and numerous unresolvable mysteries remain. Ho-kwang Mao proposes to use his newly developed high-pressure multigrain crystallographic (MGC) technology to delineate the crystal structures of the mantle rock in-situ under the DLM conditions, and use the focused ion beam technique combined with electron microscope to probe the compositions of various mineral phases in the quenched samples. The results will shed light on many key features of the DLM, including the geochemical reservoir, the core-mantle exchange, the source of mantle convection, the root of rising plumes and the graveyard of subducted plates. The prevailing theory was that the majority of the lower mantle is made up of a ferromagnesian silicate, (Mg,Fe)SiO3, called bridgmanite. It was thought that this mineral did not change structure over the enormous range of pressures and temperatures found in the lower mantle except at the very bottom D" layer beyond 110 gigapascals. Very recently, in simulating the conditions of the lower mantle using laser-heated diamond anvil cells brought to pressures between 95 and 101 gigapascals and temperatures between 2,200 and 2,400 Kelvin, Mao's team found that ferromagnesian bridgmanite is unstable. It disassociates into two phases: one magnesium silicate bridgmanite without the iron, which is represented by the Fe-free portion of the chemical formula, and one iron-rich and hexagonal in structure, called the H-phase. Further tests showed that this iron-rich H-phase is more stable than when the iron is incorporated in the ferromagnesian bridgmanite, much to everyone's surprise. There could be many more unidentified phases down there in the DLM as well, waiting to be identified by the present project. Discoveries and characterizations of these phases will lead to a fundamentally new paradigm of the deep Earth.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/67837
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Ho-kwang Mao.Renewal: Petrology and Geochemistry of the Deep Lower Mantle.2015.