Mineral Crushing Methods for Noble Gas Analyses of Fluid Inclusions

Abstract

Noble gases are frequently probed for investigating fluid inclusions in minerals to unravel rock-forming processes through time. Over the last decades, heating and crushing have been the two main methods applied for noble gas extraction from fluid inclusions in ultrahigh vacuum (about 10-9 mBar). The heating of minerals or pieces of bulk rock causes the release of noble gases from both fluid inclusions and the mineral or rock matrix, the latter due to temperature-dependent mineral dehydration. Crushing of minerals only affects fluid inclusions and allows a release of noble gases at room temperature with minor contributions from the mineral matrix. This review describes different ultravacuum crushing techniques for noble gas analysis from fluid inclusions. It examines the technical details and operational conditions of each crushing system as well as methods to prepare samples prior to crushing. Crushing systems were found to have unique designs across the different laboratories reviewed; they include single or multiple sample loadings and manual, magnetic, or hydraulic operation of the crushing pistons. Due to the small amounts of noble gases released, the technology requires several mg to a few grams of rock material to achieve a measurement of all stable noble gas isotopes in a single fluid inclusion. While theoretically all stable noble gas isotopes are of interest, the elements and isotopes reported in different studies vary widely and reference materials as well as laboratory intercomparisons are lacking. The review includes applications on the origins of magmatic rocks and geochemical processes in the Earth’s mantle, the origin and chemical composition of deep crustal fluids and how these contribute to the formation of minerals of economic interest, and paleoclimate studies based on speleothems.