Melting relations of muscovite to 30 kilobars in the system KAlSi_3O_8-Al_2O_3-H_2O
1973
Mixtures of synthetic muscovite, sanidine, and muscovite-sanidine, with
or without water, were reacted in piston-cylinder apparatus between 10 and 35 kb.
Phases produced include muscovite(Ms), KAlSi_3O_8H_2O(OrH), sanidine(Or), corundum(Co), liquid(L), and vapor(V). Melting reactions determined are: (a) Ms ⇔ Or +
Co + L, (b) Ms + V ⇔ Co + L, (c) Ms + Or + V ⇔ L, (cl) Or + V⇔ L.
Temperatures of univariant curves are, at 15 kb, (a) 885° (b) 855° (c) 780° (d) 795°;
and at 30 kb, (a) 1010° (b) 935 ° (c) 720° (d) 755 °. At 30 kb the vapor-absent melting
reaction (a) is 75° higher than the corresponding reaction (b) with excess vapor.
Extrapolation of these melting reactions downward places close limits on the invariant
point at 9.5 kb and 825°C for the coexistence of Ms + Or + Co + L + V and defines
the high pressure limits for reactions Ms ⇔Or + Co + V, and Or + Co +
V ⇔ L. This facilitates selection from among the varied muscovite dehydration reaction
curves previously published.
Comparison of the muscovite stability range with published estimates of temperature
distribution in subducted lithosphere slabs suggests that muscovite in subducted
sediments neither contributes water for magmatic processes beyond the arc-trench gap
nor influences the chemical variations in lavas across an arc complex. It dissociates
or melts at shallower depths.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
0
References
14
Citations
NaN
KQI