In-situ characterization of the trace element signatures, with special emphasize to the REE pattern, of Ca-rich mineral and fluid inclusions in diamonds from a super-deep source.

对超深层钻石中富钙矿物和流体包裹体的微量元素特征进行原位表征，特别强调稀土元素模式。

• 批准号: 427321448
• 负责人: Professor Dr. Frank Erich Brenker
• 金额: --
• 依托单位: Department of Earth and Atmospheric Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/427321448?language=en
• 关键词: situ; characterization; trace; element; signatures

Trace element pattern, including the relative abundance of rare earth elements (REE), are an important tool to decipher the origin and geological history of minerals and rocks. Whereas these signatures and related processes are quite well known for crustal materials and the lithospheric upper mantle, direct data on the deeper Earth are still scarce.Studies of REE of inclusions in diamonds with a suggested super deep origin (asthenospheric upper mantle, transition zone and lower mantle) demonstrate that CaSiO3-perovskite might be the main host of these trace elements within the deep Earth. For most rock chemistries, it is experimentally demonstrated that a CaSiO3-Phase will only exists at pressures related to depths of the lower transition zone and the lower mantle of the Earth. However, it was already shown that at least some of these CaSiO3-inclusions found in super deep diamonds originate in the upper mantle most likely from carbonatitic melts.In this proposal we plan to apply a variety of non-destructive “in-situ” techniques, with special emphasize to novel advanced Synchrotron X-ray beam techniques developed or improved by our group. The main task will be to determine the REE and trace element inventory of a subset of carbonaceous and therefore potentially REE-rich mineral and fluid inclusions in diamonds with a suggested super deep origin. The goal will be to characterize and compare different subsets with various suggested depths and processes of origin. These include inclusions suites with likely lower mantle (CaSiO3+MgSiO3+-MgO), transition zone (CaSiO3+Ringwoodite) or upper mantle (CaSiO3+Ca2SiO4) origin, as well as CaSiO3-CaTiO3 intergrowths, Ca-carbonates, Ca-phosphates and related trapped REE-rich fluids.In contrast to any effort before, based on our new technical developments at DESY (Hamburg) and the ESRF (Grenoble), we are now able to quantitatively determine all REE with a spatial resolution of well below a micron, of inclusions still trapped within the diamond host. This enables to measure very tiny (below 1 micron), very fragile (like carbonates) or very complex inclusions and attached fluid films. This type of measurement is possible by the use of a novel plate detector technology, which enables fast and simultaneous wavelength dispersive X-ray fluorescence analyses of all REE at high spatial resolution (~ 100nm) and low detection limits (< 1ppm). As REE and trace element patterns are crucial to decipher the geological history of minerals and rocks it might help to constrain their origin and source region within the heterogeneous mantle.

微量元素模式，包括稀土元素的相对丰度，是破译矿物和岩石成因和地质历史的重要工具。虽然这些特征和相关过程对于地壳物质和岩石圈上地幔来说是众所周知的，但关于地球更深部的直接数据仍然很少。对具有可能的超深源(软流圈上地幔、过渡带和下地幔)的钻石中包裹体的稀土元素研究表明，CaSiO_3-钙钛矿可能是这些微量元素在地球深处的主要寄主。对于大多数岩石化学来说，实验证明，CaSiO_3相只存在于与地球下部过渡带和下地幔深度相关的压力下。然而，已经证明，在超深部钻石中发现的这些CaSiO_3包裹体中，至少有一部分来自上地幔，最有可能来自碳酸盐岩熔体。在这项建议中，我们计划应用各种非破坏性的原位技术，特别是我们小组开发或改进的新型先进的同步辐射X射线束技术。主要任务将是确定一小部分碳质矿物和流体包裹体的稀土元素和微量元素清单，这些矿物和流体包裹体可能富含稀土元素，这些矿物和流体包裹体被认为是超深源钻石。目标将是用不同的建议深度和成因过程来表征和比较不同的子集。这些包裹体包括可能来自下地幔(CaSiO_3+MgSiO_3+-MgO)、过渡带(CaSiO_3+环形岩浆)或上地幔(CaSiO_3+Ca2SiO_4)的包裹体，以及CaSiO_3-CaTiO_3共生的包裹体、钙碳酸盐、钙磷酸盐和相关的富含稀土元素的圈闭流体。与以前的任何努力相比，基于我们在DESY(汉堡)和ESRF(格勒诺布尔)的新技术发展，我们现在能够定量确定仍捕获在钻石寄主中的包裹体的空间分辨率远低于微米的所有稀土元素。这使得能够测量非常微小(小于1微米)、非常脆弱(如碳酸盐)或非常复杂的夹杂物和附着的流体薄膜。这种类型的测量是通过使用一种新的平板探测器技术实现的，该技术能够在高空间分辨率(~100 nm)和低检测下限(1ppm)下对所有稀土元素进行快速和同时的波长色散X射线荧光分析。由于稀土元素和微量元素模式对破译矿物和岩石的地质历史至关重要，这可能有助于限制它们在非均质地幔中的来源和源区。