Unexpected phase assemblages in inclusions with ternary H2O-salt fluids at low temperatures

Abstract

Phase assemblages and temperatures of phase changes provide important information about the bulk properties of fluid inclusions, and are typically obtained by microthermometry. Inclusions are synthesized in natural quartz containing an aqueous fluid with a composition in the ternary systems of H 2 O-NaCl 2 -CaCl 2 , H 2 O-NaCl-MgCl 2 , and H 2 O-CaCl 2 -MgCl 2 . This study reveals that these fluid inclusions may behave highly unpredictably at low temperatures due to the formation of metastable phase assemblages. Eutectic temperatures cannot be detected in most of the fluid inclusions containing these ternary systems. Nucleation of a variety of solid ice and salt-hydrate phases in single fluid inclusions is often partly inhibited. Raman spectroscopy at low temperatures provides an important tool for interpreting and understanding microthermometric experiments, and visualizing stable and metastable phase assemblages. Final dissolution temperatures of ice, salt-hydrates, and salt must be treated with care, as they can only be interpreted by purely empirical or thermodynamic models at stable conditions. Keywords

Freezing and melting behaviors of H2O‐NaCl‐CaCl2 solutions in fused silica capillaries and glass‐sandwiched films: implications for fluid inclusion studies

“…It has been recognized by many previous studies (e.g., Roedder , ; Davis et al . ; Baumgartner & Bakker ; Bakker & Baumgartner ) that H 2 O‐NaCl‐CaCl 2 fluid inclusions exhibit various freezing and melting behaviors during the heating process after they had been cooled to very low temperatures (e.g., −185°C), before reaching the eutectic temperature (−52°C). Pre‐eutectic behaviors, including darkening of the inclusion (Davis et al .…”

“…The metastability below the eutectic temperature is further complicated by the development of tetrahydrate and sinjarite in addition to the stable assemblage of ice + hydrohalite + antarcticite (Samson & Walker ; Ni et al . ; Baumgartner & Bakker ; Bakker & Baumgartner ; Chi et al . ; Chu & Chi ).…”

“…; Bakker ; Ni et al . ; Baumgartner & Bakker , ; Bakker & Baumgartner ) and in laboratory‐grown halite crystals (Davis et al . ), fused silica capillaries (Chou et al .…”

Magmatic Hydrothermal Fluids at the Sedimentary Rock-Hosted, Intrusion-Related Telfer Gold-Copper Deposit, Paterson Orogen, Western Australia: Pressure-Temperature-Composition Constraints on the Ore-Forming Fluids

“…This very low eutectic 13 temperature may also represent a metastable phase transition instead of true first melting, so the implications for salt composition has to be taken with care (e.g., Bakker and Baumgartner, 2012 This interpretation is further corroborated by the solubility of calcite that decreases with increasing temperature at the T-Xsalinity conditions measured for these inclusions (Fein and Walther, 1987;Caciagli and Manning, 2003). Although no carbonic phases (e.g., CO2, CH4)…”

European Current Research on Fluid Inclusions — ECROFI XXI Leoben (Austria)

“…Experimental work with synthetic fluid inclusions on H 2 Osalt systems is presented by Ronald J. Bakker and Miriam Baumgartner [7]. They illustrate a number of metastabilities and a number of different phase assemblages that may regularly occur in H 2 O-NaCl-CaCl 2 , H 2 O-NaCl-MgCl 2 , and H2O-CaCl 2 -MgCl 2 fluid systems in inclusions at low temperatures.…”