H2O in nominally anhydrous mineral inclusions in diamonds and the volatile composition of diamond forming media

IF 4.8 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Earth and Planetary Science Letters Pub Date : 2025-03-27 DOI:10.1016/j.epsl.2025.119311

Andrea Curtolo , Maxwell C. Day , Francesca Innocenzi , Nathalie Bolfan-Casanova , Martha G. Pamato , Simon Falvard , Fabrizio Nestola , Jeff W. Harris , Davide Novella

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引用次数: 0

Abstract

Many studies have investigated the H₂O content of mantle minerals in xenoliths, which in various cases show evidence of metasomatism, implying that the measured H₂O contents may reflect these modification processes rather than the H₂O content in the environment where they were sourced. In this work, the H₂O content of 118 mineral inclusions in lithospheric diamonds, that are shielded from metasomatic and alteration events by their diamond host, was investigated.

Most of the inclusions studied here are clinopyroxene and garnet of eclogitic and peridotitic paragenesis and their H₂O content was determined by recording Fourier Transform Infrared (FTIR) spectra of each inclusion within their diamond host. Additional analyses conducted on seven inclusions that were extracted from their diamond host show good agreement with the analysis performed while still trapped inside the diamond, confirming the validity of the H₂O contents determined for the inclusions still trapped by their diamond host. The measured H₂O contents range from 0 to 550 ppm wt. with eclogitic inclusions showing a higher H₂O content with respect to their peridotitic counterparts. On average, clinopyroxene has the highest H₂O content compared to all other inclusion minerals (with average H₂O content of 110 ppm wt. and 61 ppm wt. for eclogitic and peridotitic samples, respectively). The H₂O contents of mineral inclusions in diamonds studied here and from the literature are much lower than those reported for cratonic mantle xenoliths. This difference may be due to (i) sampling bias, (ii) metasomatism subsequent to diamond formation, or (iii) lithospheric mantle involved in diamond formation not being representative of the average cratonic lithosphere (i.e., with a different H₂O activity). Modelled H diffusion in mineral inclusions in diamonds at the pressure and temperature conditions of diamond formation is fast, indicating complete H₂O re-equilibration with the diamond forming medium. It follows that the diamond forming medium must be a silicate melt with a low H₂O content, a carbonatitic melt and/or a fluid characterized by a low H₂O activity.

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H2O是金刚石中名义上无水的矿物包裹体和金刚石形成介质的挥发性成分

许多研究调查了捕虏体中地幔矿物的H2O含量，在各种情况下显示出交代作用的证据，这意味着测量的H2O含量可能反映了这些修饰过程，而不是它们来源环境中的H2O含量。本文研究了岩石圈钻石中118种矿物包裹体的水含量，这些包裹体被钻石宿主屏蔽，不受交代和蚀变事件的影响。本文研究的包裹体大多为榴辉石和榴石共生的榴辉石和榴石，通过记录每个包裹体在其金刚石宿主体内的傅里叶变换红外（FTIR）光谱来确定其H2O含量。对从钻石宿主中提取的7个包裹体进行了进一步分析，结果与仍被困在钻石内部的包裹体的分析结果吻合良好，证实了对仍被钻石宿主捕获的包裹体测定的H2O含量的有效性。测得的水含量范围为0 ~ 550ppm，其中榴辉岩包裹体的水含量高于其橄榄岩包裹体。与所有其他包裹体矿物相比，斜辉石的平均水含量最高（榴辉岩和橄榄岩样品的平均水含量分别为110 ppm和61 ppm）。本文和文献研究的钻石矿物包裹体的H2O含量远低于克拉通地幔捕虏体。这种差异可能是由于(i)采样偏差，（ii）钻石形成后的交代作用，或（iii）钻石形成过程中涉及的岩石圈地幔不具有平均克拉通岩石圈的代表性（即具有不同的水活性）。在钻石形成的压力和温度条件下，模拟的H在钻石矿物包裹体中的扩散速度很快，表明H2O与钻石形成介质完全再平衡。由此可见，金刚石形成介质必须是低H2O含量的硅酸盐熔体、碳酸盐岩熔体和/或以低H2O活性为特征的流体。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Earth and Planetary Science Letters 地学-地球化学与地球物理

CiteScore

10.30

自引率

5.70%

发文量

475

审稿时长

2.8 months

期刊介绍： Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.