The abundance and isotopic composition of the noble gases in ancient fluids

Abstract

Analysis of noble gases released from fluid inclusions by stepwise in vacuo crushing promises to provide for palaeocrustal fluids the wealth of information currently being obtained from the analysis of noble gases in contemporary ground-waters. In this paper, we report preliminary analyses and interpretation of noble-gas abundances and isotopes in: (a) minerals that precipitated in equilibrium with the atmosphere, in order to identify trapped air-saturated water; (b) quartz and fluorite from the North Pennines orrefield, to provide evidence on the source and interactions of the mineralising fluids; (c) Rhynie chert and associated vein quartz, an example of Devonian hot-spring activity; and (d) fluid inclusion-bearing mantle minerals, with MORB-type RbSr and SmNd isotope systematics.

Not surprisingly, these measurements indicate that many of the features of modern fluids are seen in palaeo-fluids. An important practical problem appears to be the presence of an additional component of unfractionated atmosphere in some samples.