American Mineralogist, Volume 83, pages 11271132, 1998
Algorithmic modifications extending MELTS to calculate subsolidus phase relations
PAUL D. ASIMOW1,
* and MARK S. GHIORSO2
Lamont-Doherty Earth Observatory, Palisades, New York 10964-8000, U.S.A.
Department of Geological Sciences, University of Washington, Seattle, Washington 98195-1310, U.S.A.
Algorithmic modifications to the MELTS software package are presented in order that
calculations of heterogeneous phase equilibria can be performed in the subsolidus. Methods
are presented for: (1) selecting an ``initial guess assemblage'' that satisfies the bulk com-
position constraints; (2) detecting saturation of new phases (including liquid) in an assem-
blage; (3) adding and removing phases from the assemblage without adjusting the system
bulk composition; and (4) constraining the assemblage to a fixed f . These methods haveO2
been added to MELTS, allowing it to calculate heterogeneous phase equilibria with or
without liquid, closed or open to O, and with fixed intensive variables (P,T), (P,S), (P,H),
or (V,T). Applications include fractional melting calculations, metamorphic phase equilib-
ria, and geophysical models of subsolidus regions of the Earth.