In this paper, we discuss the use of x-ray absorption fine structure (XAFS) techniques for the determination of structure of metal complexes in fluid inclusions heated to elevated temperatures. Analysis of Zn K-edge XAFS spectra measured from a single hypersaline fluid inclusion in quartz shows that the ZnCl4
2- complex is dominant at all temperatures up to and including 430 °C. The Zn-Cl bond length was found to decrease uniformly with temperature, up to nearly 2% at 430 °C in comparison to the value at 25 °C. The Zn-Cl mean-square relative displacement increased linearly with temperature, from a value of 0.0043 Å2 at 25 °C to 0.0089 Å2 at 430 °C.