Insights into the behaviour of S, F, and Cl at Santiaguito Volcano, Guatemala, from apatite and glass
Insights into the behaviour of S, F, and Cl at Santiaguito Volcano, Guatemala, from apatite and glass
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DOI：
10.1016/j.lithos.2015.07.004
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发表时间：
2015-09
期刊：
影响因子：
3.5
通讯作者：
J. Scott;M. Humphreys;T. Mather;D. Pyle;M. Stock
中科院分区：
文献类型：
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作者：
J. Scott;M. Humphreys;T. Mather;D. Pyle;M. Stock
矿物磷灰石可以将所有主要的岩浆挥发性物质结合到其结构中。在熔融包裹体是不可用的，岩浆磷灰石可能因此代表了一个机会，以量化在喷发前的熔体中的挥发性浓度。我们分析了20世纪20年代至2002年期间从危地马拉卡萨基托火山喷发的安山岩和英安岩中的磷灰石和基质玻璃。X射线成像显示磷灰石颗粒中硫的复杂分区，但通常具有富硫核和贫硫边缘。磷灰石微斑晶相对于包裹体富F贫Cl。基质玻璃为英安岩至流纹岩，含氟量低，但含氯量高达2400 ppm。总的来说，数据是一致的逐步耗尽的Cl在最进化的熔体由于结晶和脱气。在没有原始熔体包裹体，我们使用磷灰石，连同公布的分区数据，重建可能的挥发性成分的喷发前熔体，因此估计长期平均气体排放量的SO2，HF和HCl的持续喷发。数据表明，二氧化硫的时间平均排放量高达157吨/天，氯化氢为74-1382吨/天，氟化氢高达196吨/天。磷灰石可以提供一个有用的措施，长期挥发性排放量在火山，直接排放量的测量，或与间歇性气体采样方法进行比较。然而，关于磷灰石的挥发分分布系数及其随温度和压力的变化仍然存在很大的不确定性。
The mineral apatite can incorporate all of the major magmatic volatile species into its structure. Where melt inclusions are not available, magmatic apatite may therefore represent an opportunity to quantify volatile concentrations in the pre-eruptive melt. We analysed apatites and matrix glasses from andesites and dacites erupted from Santiaguito Volcano, Guatemala, between the 1920s and 2002. X-ray mapping shows complex zoning of sulphur in the apatite grains, but typically with sulphur-rich cores and sulphur-poor rims. Apatite microphenocrysts are enriched in F and depleted in Cl relative to inclusions. Matrix glasses are dacite to rhyolite and contain low F but up to 2400 ppm Cl. Overall, the data are consistent with progressive depletion of Cl in the most evolved melts due to crystallisation and degassing. In the absence of pristine melt inclusions, we used apatite, together with published partitioning data, to reconstruct the likely volatile contents of the pre-eruptive melt, and hence estimate long-term average gas emissions of SO2, HF and HCl for the ongoing eruption. The data indicate time-averaged SO2emissions of up to 157 tonnes/day, HCl of 74–1382 tonnes/day and up to 196 tonnes/day HF. Apatite may provide a useful measure of long-term volatile emissions at volcanoes where direct emissions measurements are unavailable, or for comparison with intermittent gas sampling methods. However, significant uncertainty remains regarding volatile distribution coefficients for apatite, and their variations with temperature and pressure.