Experimental study of chlorine behavior in hydrous silicic melts
- CEN-Saclay, Gif-sur-Yvette (France)
- Brown Univ., Providence, RI (United State)
Chlorine solubility in silicate melts has been investigated at 830-850 {plus minus} 5C and at pressures ranging from 50 to 200 MPa, using both natural (pantellerite, rhyolite, phonolite) and synthetic (SiO{sub 2}-Al{sub 2}O{sub 3}-K{sub 2}O-Na{sub 2}O) compositions and a stated H{sub 2}O-NaCl-KCl fluid phase near 4 molal. At 100 MPa, Cl contents in pantelleritic melts reach a solubility plateau at initial aqueous phase molality near 2. This plateau coincides with a large immiscibility gap between aqueous and chloride-rich fluids. With the coexisting Cl-saturated aqueous phase, Cl ranges from 2,720 {plus minus} 120 ppm in rhyolite to 8,960 {plus minus} 85 ppm in pantellerite and reaches 6,270 {plus minus} 170 ppm in phonolite, at 100 MPa. Between 50 and 200 MPa, the Cl content in pantelleritic melt decreases from 9,640 {plus minus} 200 ppm to 5,040 {plus minus} 150 ppm. Although Cl solubility increases with increasing FeO{sup *} in high SiO{sub 2} melts, it is mainly controlled by the Al/Si and (Na + K)/Al molar ratios of the melt with a minimum at Na + K/Al = 1 in a series of synthetic rhyolitic to pantelleritic melts. The experimental results suggest that chlorine occurs as alkali-chloride complexes in high SiO{sub 2} melts. They also indicate that Cl is concentrated in the aqueous fluids in equilibrium with SiO{sub 2}-rich melts, the exact value of D depending on melt composition and melt chlorine concentration. Volcanic degassing will create chlorine-rich hydrothermal fluids and decrease chlorine melt content.
- OSTI ID:
- 5263105
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 56:2; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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