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- Title
An experimental study on the influence of fluorine and chlorine on phase relations in peralkaline phonolitic melts.
- Authors
Giehl, Christopher; Marks, Michael; Nowak, Marcus
- Abstract
Fluorine and chlorine affect phase stabilities in magmatic rocks. We present phase equilibrium experiments investigating a peralkaline and iron-rich phonolitic composition with variable F and Cl contents. The starting composition represents a dyke rock, which is a possible parental melt to the peralkaline Ilímaussaq plutonic complex (South Greenland). Experiments were performed at 100 MPa, 1,000-650 °C and low oxygen fugacity adjusted with graphite-lined gold capsules in an internally heated argon pressure vessel and rapid quench cold seal pressure vessels. To cover this large T interval, we applied a two-step fractional crystallization strategy where glasses representing residual melt compositions at 800 °C were synthesized as starting material for consecutive experiments at lower T. In these experiments, oxidized starting glasses allocate oxygen by reduction of ferric iron and up to 1.2 wt% dissolved OH form through reaction with hydrogen provided by the pressure medium (HO) in initially dry experiments. For OH determination, hydrated super-liquidus experiments in Au capsules were performed to calibrate the extinction coefficient for the fundamental OH stretching vibration using infrared spectroscopy ( ε = 48 ± 3 L mol cm). Observed mineral phases in our experiments are titanomagnetite, fayalitic olivine, clinopyroxene, aenigmatite (NaFeTiSiO), alkali feldspar and nepheline (±native iron) coexisting with residual melt. Above 1.5 wt% F concentrations, fluorite (CaF) and hiortdahlite (CaZrSiOF) are stable in favor of Ca-rich clinopyroxene. Sodalite (NaAlSiOCl) and eudialyte (NaCaFeZrSiO(OH)Cl) form at Cl concentrations of 0.2-0.5 wt% (depending on T) and ZrO concentrations >0.7 wt% are additionally needed to stabilize eudialyte and hiortdahlite. Therefore, F and Cl may become compatible in such systems and have the potential to influence F/Cl melt ratios in evolving magmas.
- Subjects
FLUORINE; CHLORINE; MAGMAS; ARGON; CRYSTALLIZATION; INFRARED spectroscopy; IGNEOUS intrusions; EUDIALYTE
- Publication
Contributions to Mineralogy & Petrology, 2014, Vol 167, Issue 3, p1
- ISSN
0010-7999
- Publication type
Article
- DOI
10.1007/s00410-014-0977-7