From fluid inclusion microanalysis to large-scale hydrothermal mass transfer in the Earth's interior

Abstract

This paper illustrates how the recent development of microanalytical techniques for major- and trace-elements in fluid and melt inclusions contributes to the quantitative understanding of lithosphere-scale chemical transport by hydrothermal fluids, including the formation of mineral deposits. After an introductory remark on aspects of instrumentation and data quality assessment, the first-order controls of crustal fluid compositions are discussed, indicating that trace-element concentrations broadly follow silicate rock buffered conditions. However, field-based studies of texturally controlled ore-forming liquid and vapour inclusions in specific upper-crustal magmatic centres show that effective ore formation is a disequilibrium process, requiring deviations of fluid composition from the crustal rock buffers. Microanalytical techniques are also changing experimental approaches in the laboratory, allowing fluid trapping experiments for investigating mineral solubilities, melt-fluid distribution constants, and the chemical properties of fluids responsible for selective element transfer from the downgoing slab to the melting region of calc-alkaline magmas in the mantle wedge.