Abstract The compositions of volatiles in magmas can be estimated using melt inclusions encapsulated in phenocrysts. Shrinkage bubbles are occasionally observed in natural and rehomogenized melt inclusions. Because of the low solubility of CO2 in melts, CO2 is partitioned in both the melts and shrinkage bubbles in melt inclusions. We developed a method to determine total CO2 in melt inclusions by measuring (1) CO2 concentration in glass with secondary-ion mass spectrometry, (2) CO2 density in bubbles with micro-Raman spectrometry, and (3) bubble/glass volume ratio with micro X-ray computed tomography on rehomogenized melt inclusions. We applied this method to olivine-hosted melt inclusions in high-μ (HIMU)-type ocean island basalts from Raivavae in Austral Islands in French Polynesia. The shape of melt inclusions is predominantly related to their size; larger melt inclusions tend to be more angular than smaller ones. The volume of large melt inclusions may be overestimated by previous approaches in which the dimension of melt inclusions was measured by microscopy and the volume was calculated assuming ellipsoidal shape. CO2 dissolved in glass in rehomogenized melt inclusions ranges up to ~7000 ppm. The glass with a more alkalic composition shows greater CO2 concentration than that with a less alkalic composition in accordance with the composition-dependent CO2 solubility. By contrast, the correlation between the total CO2 content and the chemical composition of the glass is unclear because CO2 in shrinkage bubbles is generally greater than that in the glass. Some melt inclusions demonstrate an extremely high total CO2 content (up to 25,000 ppm). Because these melt inclusions show a large bubble volume proportion in melt inclusions (>12 vol%), they are likely formed by the simultaneous entrapment of melts and fluids during the host olivine growth. Excluding these melt inclusions, the total CO2 content and CO2/Nb ratio in melt inclusions were up to 7000 ppm and 200, respectively. This study offers an accurate determination of CO2 concentration and CO2/Nb of the HIMU basalts from Raivavae.

中文翻译：

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用收缩气泡测定熔体夹杂物中的总 CO2

摘要 岩浆中挥发物的组成可以用包裹在斑晶中的熔体包裹体来估计。在天然和再均质的熔体夹杂物中偶尔会观察到收缩气泡。由于 CO2 在熔体中的溶解度低，CO2 被分配在熔体和熔体夹杂物中的收缩气泡中。我们开发了一种测定熔体夹杂物中总 CO2 的方法，方法是测量 (1) 使用二次离子质谱法测量玻璃中的 CO2 浓度，(2) 使用微拉曼光谱法测量气泡中的 CO2 密度，以及 (3) 气泡/玻璃体积比再均质化熔体夹杂物的显微 X 射线计算机断层扫描。我们将此方法应用于法属波利尼西亚南部群岛 Raivavae 的高 μ (HIMU) 型海洋岛玄武岩中的橄榄石熔体包裹体。熔体夹杂物的形状主要与其尺寸有关；较大的熔体夹杂物比较小的熔体夹杂物更有棱角。以前的方法可能会高估大熔体夹杂物的体积，其中通过显微镜测量熔体夹杂物的尺寸，并假设椭圆体形状计算体积。溶解在玻璃中重新均质化的熔体夹杂物中的 CO2 范围高达 ~7000 ppm。根据组成依赖的 CO2 溶解度，具有较多碱性组成的玻璃比具有较少碱性组成的玻璃显示出更高的 CO2 浓度。相比之下，CO2 总含量与玻璃化学成分之间的相关性尚不清楚，因为收缩气泡中的 CO2 通常大于玻璃中的 CO2。一些熔体夹杂物显示出极高的 CO2 总含量（高达 25,000 ppm）。因为这些熔体包裹体在熔体包裹体中显示出很大的气泡体积比例 (>12 vol%)，它们很可能是由在主体橄榄石生长过程中同时夹带熔体和流体形成的。排除这些熔体夹杂物，熔体夹杂物中的总 CO2 含量和 CO2/Nb 比分别高达 7000 ppm 和 200。这项研究提供了对来自 Raivavae 的 HIMU 玄武岩的 CO2 浓度和 CO2/Nb 的准确测定。熔体夹杂物中的总 CO2 含量和 CO2/Nb 比分别高达 7000 ppm 和 200。该研究提供了对来自 Raivavae 的 HIMU 玄武岩的 CO2 浓度和 CO2/Nb 的准确测定。熔体夹杂物中的总 CO2 含量和 CO2/Nb 比分别高达 7000 ppm 和 200。这项研究提供了对来自 Raivavae 的 HIMU 玄武岩的 CO2 浓度和 CO2/Nb 的准确测定。