A new method for dating late Quaternary submarine eruptions and its use to investigate magmatic and eruptive processes at island arc volcanoes

从伊豆大岛过去的山脊喷发中提取新的海底玄武岩熔岩样品，用FTIR进行挥发性分析。这些包括来自原始岩石收藏的新碎片，以及最近在该地区巡航收集的新样本。样品被制备成晶圆片、单个玻璃碎片和熔体内含物。低挥发性浓度对薄样品的分析不确定度很大，仍然存在一些困难。这种巨大的分析不确定性使这些数据无法用于根据喷发时间以来海平面（喷发压力）的变化来估计喷发年龄。因此，FTIR分析仍在继续，目的是制备足够厚度的适当玻璃样，以减小分析不确定度。同时，合作者Usui分析了一部分样品的古磁性强度。通过结合这些样品的古磁场强度和地球化学数据，有可能限制它们的喷发年龄（目前没有挥发性数据和海平面估计）。这些数据表明喷发年龄相对较年轻，与已知年龄的陆地喷发的地层关系相一致。关于这个主题的手稿已经提交，目前正在修订中。

New samples of submarine basaltic lavas from past ridge eruptions of Izu-Oshima were prepared for volatile analysis by FTIR. These include new pieces from the original rock collection as well as new samples collected by a recent cruise in the area. Samples have been prepared as wafers, as individual glass shards, and as melt inclusions. There is still some difficulty with low volatile concentrations giving large analytical uncertainties for thin samples. This large analytical uncertainty prevents these data being used for estimating eruption age from the change in sea level (eruption pressure) since the time of eruption. FTIR analysis is therefore continuing, with the aim of preparing suitably glassy samples of sufficient thickness for smaller analytical uncertainties. Meanwhile, magnetic paleointensity of a subset of samples has been analysed by collaborator Usui. By combining the magnetic paleointensity and geochemistry data for these samples, it is possible to constrain their eruption ages (without volatile data and sea level estimation, for now). The data suggest relatively young eruption ages, consistent with their stratigraphic relation to onland eruptions of known age. A manuscript on this topic has been submitted and is currently under revision.