Determination of ions in individual fluid inclusions by laser ablation optical emission spectroscopy: development and applications to natural fluid inclusions

Abstract

Chemical data on the composition of individual fluid inclusions are required to model paleofluid-rock interactions, as these inclusions are the direct remains of the former fluid circulation in the earth's crust. The proposed technique of laser ablation coupled with optical emission spectrometry (LA-OES) determines ion ratios in individual fluid inclusions. The radiations of the elements present in the plasma are analysed with a spectrometer equipped with a pulsed and gated multichannel detector. The lateral resolution is around 6 µm and the depth of the quartz crater obtained for one laser shot is around 1 µm. For fluid inclusions, the laser beam is initially focused on the surface of the sample, to drill until the inclusion is reached, then the liquid is analysed. Plasma temperature studies showed that various kinds of standards (synthetic glasses, fluid inclusions and minerals) can be used for the establishment of calibration curves for Na/K, Na/Ca and Na/Li ratios. As the emission line intensity is a function of the ablated mass, only emission line ratios between two elements are used. In addition, a self-absorption process was considered for the calibration strategy. The relative standard deviations of the calibration curves vary from 5% (glasses) to 25% (fluid inclusions) and the detection limits are those required for the determination of ions in individual inclusions (Na and Li 10, Ca 20 and K 750 ppm). Natural fluid inclusions were analysed using the LA-OES technique and it is now possible to determine the ratios of major elements in individual fluid inclusions.