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本过程。矿物包裹体的产状提供了有关包裹体钻石形成条件的重要信息。虽然钻石被认为能够以各种方式形成，但通常涉及到流体或熔体相作为碳源。这种移动剂的性质非常令人感兴趣，因为它除了提供关于钻石形成过程的线索外，还可能导致地幔岩石的交代叠加。流体包裹体的存在一般仅限于特定类型的钻石(黄绿色、云彩或镀膜)，在宝石级单晶钻石中非常罕见，这些单晶钻石占回收钻石的大部分。然而，Nimis等人最近发现，在许多钻石中，围绕着各种矿物包裹体的薄层流体。(2016)，被认为是在钻石形成过程中被困的流动相。除了拉曼光谱表明存在羟基和硅外，我们对这一相的组成一无所知。该项目的目标是分析F·内斯托拉教授(意大利帕多瓦大学)提供的一套钻石中矿物包裹体周围流体层的组成。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的表征，以确定是否存在流体层以及来自钻石表面的包裹物的深度(已经对4个样品进行了这项工作)。有了这些信息，我们将使用时间分辨激光消融ICPMS，使用新安装的“快速漏斗”消融系统，并通过激光和质谱仪的对准来消除光谱偏斜。该系统提供了更高的时间分辨率，使信号与流体相更清晰地区分开来，并减少了来自相邻包裹体的混合。随着激光继续烧蚀包裹体，将获得矿物的成分信息，这些信息可以通过双组分混合系统来帮助去卷积流体信号。至少，将获得可靠的定量元素浓度比，尽管也可能对流体进行半定量的浓度估计，从而有助于限制这种负责深部岩石圈地幔中单晶宝石级钻石结晶的流动介质的组成。

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.