FTIR STUDY ON WATER CONTENT OF THE MELT INCLUSIONS IN PHENOCRYSTS FROM CHANGBAISHAN TIANCHI VOLCANO'S GREAT ERUPTION IN HOLOCENE

Abstract

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 FTIR, 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.