长白山天池火山千年大喷发岩浆含水量研究——熔融包裹体含水量的红外光谱测试

长白山天池火山在公元一千年左右曾发生过大规模喷发，其产物为大面积分布的灰白色碱流质浮岩和碎屑流，在其斑晶矿物橄榄石、钙铁辉石和碱性长石中均可见到熔融包裹体。在最主要的斑晶矿物——碱性长石中含有数量众多且个体也较大的熔融包裹体，多数含有一个以上的气泡，其中部分含有子晶，根据形貌特征的不同可分为截然不同的两组包裹体。这些熔融包裹体带有大量喷发前地下岩浆的信息，成为研究地下深部的岩浆在复杂的溢流-爆炸喷发中所发生变化的最好媒介。也是本文的研究对象，通过其中挥发份尤其是水的含量，可以推知天池火山发生大喷发的原因。经Nicolet Magna-IR 550红外光谱仪测定，这些熔融包裹体的含水量较高，达1．6％-3．6％，为当时天池火山发生了巨大规模爆炸喷发的原因提供了强有力的证据。但目前红外光谱仪的应用范围还比较有限，有待今后拓宽其应用领域。

FTIR study on water content of the melt inclusions in phenocrysts from Changbaishan Tianchi volcano's great eruption in Holocene.

Changbaishan Tianchi volcano once occurred a great eruption around 1000AD, the eruption materials of which were widely distributed gray comenditic pumice and pyroclastic flow. Melt inclusions were found in phenocrysts of olivines, hedenbergites and alkaline feldspars. The main phenocrysts, alkaline feldspars, have large quantity of melt inclusions. Most of them have more than one bubble and some of them have daughter crystals. These melt inclusions can be separated into two distinct groups according to their characteristics of shape, color and bubble. With lots of information of magma prior to eruption, these melt inclusions become the best candidates to understand the behavior of deep magma during complicated effusive and explosive eruptions. We can somehow know the reason why there occurred the great eruption through testing the volatile content, especially the water content contained in melt inclusions. Analysed by FFIR, these melt inclusions are found to have high water contents reaching 1.6%- 3.6%, which provides a powerful evidence for the reason of the great explosive eruption. But at present the application of the FTIR instruments to volcanic rocks is very limited. We hope the application field would be widened someday.