Tracing fluid sources and interactions

Methods of evaluating possible sources and interactions of ancient and modern fluids are being significantly improved by the development of new isotopic and geochemical microprobe techniques. Applications of O, C, and S isotopes are benefiting from the development of laser ablation methods capable of 0.1 permil precision on submilligram samples and ion microprobe methods capable of permil precision on nanogram regions of rock sections. The noble gases are proving themselves useful conservative tracers of fluid processes. The ubiquitous presence of air saturated water patterns testifies to the dominance of water originating at the Earth's surface, while the presence of radiogenic isotopes and 3He quantify interactions with crust and mantle respectively. The use of resonance ionisation has increased sensitivity for Xe and Kr analyses to the single atom level. Examples of fluid regimes currently under study are described. -Authors