John D. Frantz

Bio: John D. Frantz is an academic researcher from Carnegie Institution for Science. The author has contributed to research in topics: Solubility & Aqueous solution. The author has an hindex of 21, co-authored 26 publications receiving 1921 citations.

An internally consistent thermodynamic data set for phases of petrological interest

Abstract: The thermodynamic properties of 154 mineral end-members, 13 silicate liquid end-members and 22 aqueous fluid species are presented in a revised and updated data set. The use of a temperature-dependent thermal expansion and bulk modulus, and the use of high-pressure equations of state for solids and fluids, allows calculation of mineral–fluid equilibria to 100 kbar pressure or higher. A pressure-dependent Landau model for order–disorder permits extension of disordering transitions to high pressures, and, in particular, allows the alpha–beta quartz transition to be handled more satisfactorily. Several melt end-members have been included to enable calculation of simple phase equilibria and as a first stage in developing melt mixing models in NCKFMASH. The simple aqueous species density model has been extended to enable speciation calculations and mineral solubility determination involving minerals and aqueous species at high temperatures and pressures. The data set has also been improved by incorporation of many new phase equilibrium constraints, calorimetric studies and new measurements of molar volume, thermal expansion and compressibility. This has led to a significant improvement in the level of agreement with the available experimental phase equilibria, and to greater flexibility in calculation of complex mineral equilibria. It is also shown that there is very good agreement between the data set and the most recent available calorimetric data.

Fractional crystallization and mantle-melting controls on calc-alkaline differentiation trends

Abstract: The phase relations of primitive magnesian andesites and basaltic andesites from the Mt Shasta region, N California have been determined over a range of pressure and temperature conditions and H2O contents The experimental results are used to explore the influence of H2O and pressure on fractional crystallization and mantle melting behavior in subduction zone environments At 200-MPa H2O-saturated conditions the experimentally determined liquid line of descent reproduces the compositional variation found in the Mt Shasta region lavas This calc-alkaline differentiation trend begins at the lowest values of FeO*/MgO and the highest SiO2 contents found in any arc magma system and exhibits only a modest increase in FeO*/MgO with increasing SiO2 We propose a two-stage process for the origin of these lavas (1) Extensive hydrous mantle melting produces H2O-rich (>45--6 wt% H2O) melts that are in equilibrium with a refractory harzburgite (olivine + orthopyroxene) residue Trace elements and H2O are contributed from a slab-derived fluid and/or melt (2) This mantle melt ascends into the overlying crust and undergoes fractional crystallization Crustal-level differentiation occurs under near-H2O saturated conditions producing the distinctive high SiO2 and low FeO*/MgO characteristics of these calc-alkaline andesite and dacite lavas In a subset of Mt Shasta region lavas, magnesian pargasitic amphibole provides evidence of high pre-eruptive H2O contents (>10 wt% H2O) and lower crustal crystallization pressures (800 MPa) Igneous rocks that possess major and trace element characteristics similar to those of the Mt Shasta region lavas are found at Adak, Aleutians, Setouchi Belt, Japan, the Mexican Volcanic Belt, Cook Island, Andes and in Archean trondhjemite--tonalite--granodiorite suites (TTG suites) We propose that these magmas also form by hydrous mantle melting