Characterizing the fluid films surrounding inclusions in lithospheric diamond: further clues to the environment of diamond formation

钻石的形成是我们理解地球深层碳循环的基础。矿物包裹体的出现提供了有关包裹金刚石形成条件的重要信息。虽然金刚石被认为能够以多种方式形成，但流体或熔体相通常被认为是碳源。这种移动的介质的性质非常有趣，因为除了提供有关金刚石形成过程的线索外，它还可能引起地幔岩石的交代叠印。流体包裹体的存在通常仅限于特定类型的金刚石（纤维状，云状或涂层），并且在宝石级单晶金刚石中非常罕见，这构成了大多数回收的金刚石。然而，尼米斯等人（2016年）最近在许多钻石中发现了围绕各种矿物包裹体的薄流体层，并认为这代表了钻石形成过程中捕获的移动的相。除了拉曼光谱表明OH和Si的存在外，对该相的组成一无所知。该项目的目标是分析F教授提供的一组钻石中矿物包裹体周围流体层的成分。Nestola（帕多瓦大学，意大利）。作为第一步，将使用拉曼光谱和高分辨率数字显微镜对样品进行彻底表征，以确定流体层的存在和夹杂物距金刚石表面的深度（这已经对4个样品进行了）。有了这些信息，我们将采用时间分辨激光烧蚀ICPMS使用新安装的“快速漏斗”烧蚀系统结合消除光谱偏斜的激光和质谱仪的对准。该系统提供了大大改进的时间分辨率，允许从流体相的信号的“更清晰”的区别，与相邻夹杂物的混合较少。随着激光继续烧蚀到包裹体中，将获得矿物的成分信息，这可以通过双组分混合系统学来帮助对流体信号进行去卷积。最低限度，可靠的定量元素浓度比将获得，虽然半定量浓度估计也可能是流体，从而有助于限制这种移动的介质的组成，负责结晶的单晶宝石级钻石在岩石圈地幔深处。

The formation of diamond is a process fundamental to our understanding of the deep carbon cycle of the Earth. The occurrence of mineral inclusions provides important information about the conditions under which the enveloping diamond formed. Although diamond is considered to be able to form in a variety of ways, a fluid or melt phase is usually implicated as the carbon source. The nature of this mobile agent is of extreme interest since it may also cause metasomatic overprinting of mantle rocks in addition to providing clues about the process of diamond formation. The presence of fluid inclusions is generally restricted to specific types of diamond (flbrous, cloudy or coated) and are very rare in gem-quality monocrystalline diamond, which make up the majority of recovered diamonds. However, a thin fluid layer surrounding a variety of mineral inclusions in numerous diamonds has recently been identified by Nimis et al. (2016) and is considered to represent a mobile phase trapped during diamond formation. Aside from Raman spectra indicating the presence of OH and Si, nothing is known about the composition of this phase. The goal of this project is to analyze the composition of the fluid layer surrounding mineral inclusions in a set of diamonds provided by Prof. F. Nestola (University of Padua, Italy). As a first step, the samples will be thoroughly characterized to establish the presence of a fluid layer and the depth of the inclusion from the diamond surface using Raman spectroscopy and a high-resolution digital microscope (this has already been done for 4 samples). With this information we will then employ time-resolved laser ablation ICPMS using a newly installed "fast funnel" ablation system in combination with the elimination of spectral skew by alignment of laser and mass spectrometer. This system provides a much improved time resolution, allowing for a "cleaner" distinction of the signal from the fluid phase, with less mixing from the adjacent inclusion. As the laser continues to ablate into the inclusion, compositional information for the mineral will be obtained, which can be used via two-component mixing systematics to help deconvolve the fluid signal as well. At a minimum, reliable quantitative elemental concentration ratios will be obtained, although semiquantitative concentration estimates may also be possible for the fluid, thus helping to constrain the composition of this mobile medium responsible for crystallization of monocrystalline gem-quality diamonds in the deep lithospheric mantle.