Fluid Inclusion Study of Antarctic Blue Ice Gypsum

Abstract

Gypsum, the most common sulfate mineral, has a hardness of 2 on the Mohs scale and is typically formed through seawater evaporation. However, a large aggregate of gypsum was discovered within blue ice moraines on the southern side of the Sør Rondane Mountains in Dronning Maud Land at an elevation of around 2000 meters. It was exposed to a very harsh environment with temperatures below -60°C. Therefore, at -60°C, inclusions in gypsum did not maintain their original fluid densities. There has not been a lot of research conducted on this type of gypsum formation. The thesis aims to characterize the environment in which the gypsum is formed with the help of fluid inclusion studies. Petrographic observations revealed that the gypsum shows irregular growth zoning and bent cleavage planes. It contains a significant amount of primary fluid inclusions that are aligned parallel to the growth zoning and cleavage planes. These inclusions consist of both single-phase and two-phase inclusions. The single-phase liquid inclusions were primarily observed along the 010 cleavage plane of the gypsum crystals. They were characterized as being large in the x and y directions but flat in the z-direction, resulting in some inclusions having very low prograde homogenization temperatures. However, the measured prograde and retrograde homogenization temperatures of these inclusions are considered unreliable for drawing any conclusions regarding the original density of the fluid in the inclusions and the temperature-pressure conditions under which the gypsum crystals formed.