Diamonds and Other Ultra-high Pressure Minerals From Paleo-suboceanic Mantle - possible Mantle Recycling

来自古海底地幔的钻石和其他超高压矿物 - 可能的地幔回收

• 批准号: 1118796
• 负责人: Larissa Dobrzhinetskaya
• 金额: $ 25.24万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-01 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1118796&HistoricalAwards=false
• 关键词: Diamonds; Other; Ultra; Pressure; Minerals

Diamonds and other ultra-high pressure minerals from paleo-suboceanic mantle - possible mantle recyclingIntellectual merit. According to geochemical characteristics ophiolites (including podiform chromitites) are classified into two groups formed at either divergent plate boundaries or via back-arc spreading at convergent plate boundaries (i.e., supra-subduction zone settings). Podiform chromitites play a significant role in understanding the processes of melting in the suboceanic mantle, and constitute valuable ores. Origin of podiform chromitites has been attributed to: (1) crystallization from ultramafic magmas similar to banded chromitite in cumulate rocks; (2) residual material from partial melting in the upper mantle; (3) products of crystallization of mantle-derived partial melts as a result of melt/rock interaction near the Moho boundary; (4) diapiric transport (along with associated dunite and harzburgite) of materials from the core-mantle boundary via mantle plumes, and (5) formation in the deep mantle (where Cr-spinel originally formed as a high-pressure polymorph). However, recently the magmatic origin (3) of podiform chromitite is questioned by many scientists after the discovery of in-situ ultrahigh-pressure (UHP) mineral inclusions (diamond, Fe-Ti alloy, coesite pseudomorphous after stishovite, TiN, cBN, TiO2 II, and relict high-pressure polymorph of chromite with Ca-ferrite structure) in the chromitite of the Luobusa massif, Tibet. These inclusions all formed at high-pressure, corresponding to depths of 250?380 km. A two-year project is proposed to investigate unusual UHP minerals from the Luobusa chromitites to understand their relationships with host chromites and the depth and age of their formation. This work will include microstructural analysis, trace-element and isotope analyses, and characterization of fluid/melt and solid/fluid nanoinclusions in both UHP minerals and host chromite. The project will focus on two working hypotheses: (1) the UHP minerals from podiform chromitite were created at low pressure but have been subducted deeply and recycled to their current locations; (2) part, at least, of the chromitites were formed within a presumably deep channel of a paleo-supra-subduction zone and later modified by boninitic melt near the Moho. Detailed petrographic, high-resolution scanning and analytical transmission electron microscopy, focused ion beam (FIB), and nano secondary-ionization spectrometry (nano SIMS) for C,B,N,Os,Re isotopic analyses are proposed to investigate the nature of the UHP minerals. The results will open a new window to study xenomorphic UHP mineral assemblages that have not previously been observed in mantle-derived rocks. Broader impacts. The proposed project promotes utilization of advanced scientific technologies available to University of California faculties through long-term collaboration with Lawrence Livermore National Laboratory. The project will support a graduate student and two undergraduate students. The students will be taught how to work with FIB, nanoSIMS, SEM, and TEM, which together represent a frontier of 21st-century science and technologies. The project promotes a female scientist acting as PI. Integration of national laboratory (LLNL) facilities into academic research and education will strengthen ties between scientists and society, and promote understanding of the Earth?s interior and the dynamics of its internal processes. It will encourage student innovation that, in the future, will impact the competitiveness of the United States in science and technology.

来自古海底地幔的金刚石和其他超高压矿物--可能的地幔再循环。根据蛇绿岩（包括豆荚状铬铁矿）的地球化学特征，将其分为两类，一类是在扩张板块边界形成的，另一类是在会聚板块边界通过弧后扩张形成的（即，超俯冲带背景）。豆荚状铬铁矿是研究大洋地幔熔融过程的重要矿物。豆荚状铬铁矿的成因是：（1）类似于堆晶岩中的条带状铬铁矿的超镁铁质岩浆结晶作用，（2）上地幔部分熔融的残余物质，（3）莫霍界面附近地幔部分熔融结晶产物，（4）上地幔部分熔融产物，（5）上地幔部分熔融产物，（6）上地幔部分熔融产物，（7）上地幔部分熔融产物，（8）上地幔部分熔融产物，（9）上地幔部分熔融产物。（4）来自核幔边界的物质通过地幔柱的底辟搬运（沿着伴随着纯橄榄岩和方辉橄榄岩）;（5）深部地幔的形成（铬尖晶石最初形成为高压多形物）。 然而，近年来，在西藏罗布莎山铬铁矿中发现了超高压矿物包裹体（金刚石、Fe-Ti合金、柯石英、TiN、cBN、TiO 2 II、铬铁矿高压多晶型残留物和Ca-铁氧体结构），豆荚状铬铁矿的岩浆成因受到了许多科学家的质疑。这些包裹体都是在高压下形成的，对应于250？三百八十公里。提出了一个为期两年的项目，以调查不寻常的超高压矿物从罗布莎铬铁矿，以了解他们与主机铬铁矿的关系，以及他们的形成深度和年龄。这项工作将包括微观结构分析，微量元素和同位素分析，并在超高压矿物和主机铬铁矿的流体/熔体和固体/流体纳米包裹体的表征。该项目将集中于两个工作假设：（1）豆荚状铬铁矿中的超高压矿物是在低压下形成的，但已经被深深地俯冲并再循环到它们目前的位置;（2）至少有一部分铬铁矿是在古俯冲带的一个可能的深通道内形成的，后来被莫霍面附近的玻安岩熔体改变。详细的岩相学，高分辨率扫描和分析透射电子显微镜，聚焦离子束（FI B），和纳米二次电离光谱（纳米西姆斯）的C，B，N，Os，Re同位素分析，建议调查的性质的超高压矿物。这一结果将为研究幔源岩石中尚未发现的他形超高压矿物组合开辟一个新的窗口。更广泛的影响。拟议的项目通过与劳伦斯利弗莫尔国家实验室的长期合作，促进加州大学各院系利用先进的科学技术。该项目将资助一名研究生和两名本科生。学生将学习如何使用FIB，nanoSIMS，SEM和TEM，它们共同代表了21世纪科学和技术的前沿。该项目促进一名女科学家担任PI。将国家实验室（LLNL）设施纳入学术研究和教育将加强科学家与社会之间的联系，并促进对地球的了解？的内部及其内部过程的动力学。它将鼓励学生创新，在未来，这将影响美国在科学和技术方面的竞争力。