The partitioning of Mg²⁺, Fe²⁺ and Mn²⁺ ions between spinel group minerals (spinel and magnetite series minerals) and 1 molal aqueous chloride solution was experimentally investigated at 600°C and 1 kb using standard cold-seal type pressure vessels. The experiments were carried out for the following six binary systems; spinel-hercynite, hercynite-galaxite, galaxite-spinel, magnesioferrite-magnetite, magnetite-jacobsite and jacobsite-magnesioferrite. Continuous solid solutions were formed in all of the systems. The cations are preferentially partitioned into the spinel series minerals in the order of Mg²⁺>Fe²⁺>Mn²⁺, and into the magnetite series minerals in the order of Fe²⁺>Mg²⁺>Mn²⁺. The cation partitioning between spinel and magnetite series minerals was derived from the above experimental results, which indicates that the formers prefer Mg²⁺ but the latters Fe²⁺ and Mn²⁺.

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Peculiar dyke rocks rich in alkalies and other incompatible elements intrude into the Himekami and Hinomiko plutons of Zone IV in the Kitakami Mountains. Representative rock types are as follows: 1) Shoshonite with the mineral assemblage biotite-orthopyroxene-olivine-clinopyroxene-plagioclase-alkali feldspar; and 2) High-K andesite with biotite-hornblende-plagioclase-alkali feldspar-quartz. The assemblage of the first rock types is similar to those of monzogabbro, which characterizes Zone IV plutons. Phenocrysts of olivine and orthopyroxene are surrounded by small crystals of cummingtonite and pale colored biotite. Composition of olivine is Fo_74-70, while phenocryst and groundmass clinopyroxene are Wo₄₀En₄₅Fs₁₅ and Wo₄₃En₃₅ Fs₂₂ respectively, and that of phenocryst orthopyroxene has Wo₃En₇₂Fs₂₅ core and Wo₁En₅₅Fs₄₄ rim. Compositions of phenocryst plagioclase, groundmass plagioclase and alkali-feldspar are An_60-41 An_43-21 and Or_91-31 respectively. The second rock type is rather coarase and porphyritic having phenocrysts of plagioclase and hornblende, and groundmass biotite, hornblende, plagioclase, alkali feldspar, quartz, apatite and Fe-Ti oxides. Hornblende is distinctly zoned and rich in (Na+K) and Al, different from that of the Cretaceous plutons in the Kitakami Mountains.
Major element chemistry of these rocks indicates that both rock types are characteristically rich in K₂O and poor in TiO₂. They show MORB-normalized patterns poor in Nb and rich in Rb and Ba, which are characteristics of island arc or orogenic shoshonite rock series. The occurrence of these rocks provides important information as to the genesis of plutons and tectonic environments of the Kitakami Mountains during Early Cretaceous age.

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An empirical equation for quartz solubility in NaCl solution (up to 20 wt. %) is obtained from the experimental results of Anderson and Burnham (1967), Novgorodov (1978), Hemley et al. (1980), and Fournier et al. (1982). The ratio of quartz solubility in NaCl solution (Saq) to the solubility in pure water (Swatar) under the same pressure-temperature condition can be expressed by the following equation: In (Saq/Swater)=2.54583 ln(ρaq_F/ρwater), where Saq and Swater are expressed as molality, ρaq and ρwater designate the densities (g/cm³) of NaCl solution and water, respectively, and F is the weight fraction of water in the solvent.
Based on this relationship, the equation for quartz solubility proposed by Von Damm et al. (1991) is modified into the following equation: lnSaq={-2.21703+2 lnF+0.54583 ln (ρaqF/ρwater)}+2 lnρaq+(-2315.71+0.0042138T²) T^-1+0.0196606 PT^-1, where T and P denote temperature (Kelvin) and pressure (bar), respectively.

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