A method for the direct analysis of quenched, magmatic-hydrothermal fluids recovered from high-pressure, high-temperature experiments
Résumé
A method for analyzing low-salinity fluids (up to ~11 wt% NaCl equivalent) that have been equilibrated with felsic melts in high-pressure, high-temperature experiments is reported. Experiments were performed at a pressure of 200 MPa and 800 °C in internally-heated pressure vessels, wherein magmatic fluids were quenched and recovered in a multi-step process for analyses of major (Na, K, Ca, Cl, and F) and trace (Li, Be, Mn, Cu, Zn, Rb, and Sr) elements by ion chromatography and inductively coupled plasma mass spectrometry (ICP-MS). The quenched melts were analyzed for major and trace elements by electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Such analyses permitted the composition of the fluid to be directly measured without the need for mass balance calculations or trapping fluids within fluid inclusions while still enabling the precise determination of partition coefficients. Mass balance calculations tend to overestimate Na, K, Ca, and Be; underestimate Cu, Zn, and F; and are in agreement for Li, Mn, Rb, Sr, and Cl when compared to direct measurements. Additionally, a comparison of partition coefficients calculated from measured and mass balance derived concentrations to available literature data is consistent with mass balance calculations being less accurate than measured values. Thus, direct measurements of quenched fluids by ion chromatography and ICP-MS offer a robust method for characterizing the composition of magmatic-hydrothermal fluids that have been equilibrated with silicate melts.
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