A number of experiments have been conducted in order to study the equilibria between olivine and basaltic liquids and to try and understand the conditions under which olivine will crystallize. These experiments were conducted with several basaltic compositions over a range of temperature (1150-1300 ° C) and oxygen fugacity (10-°.~s-10 -12 arm.) at one atmosphere total pressure. The phases in these experimental runs were analyzed with the electron microprobe and a number of empirical equations relating the composition of olivine and liquid were determined. The distribution coefficient o, (X~o/ (Xreo) K/~- i'~-Liq \ O1 t-XFeoJ (X~go) relating the partioning of iron and magnesium between olivine and liquid is equal to 0.30 and is independent of temperature. This means that the composition of olivine can be used to determine the magnesium to ferrous iron ratio of the liquid from which it crystallized and conversely to predict the olivine composition which would crystallize from a liquid having a particular magnesium to ferrous iron ratio. A model (saturation surface) is presented which can be used to estimate the effective solubility of olivine in basaltic melts as a fune¢ioa of temperature. This model is useful in predicting the temperature at which olivine and a liquid of a particular composition can coexist at equilibrium.

http://www.mantleplumes.org/WebDocuments/RoederEmslie.pdf

Olivine-Liquid Equilibrium

Use of simple mixing models of orthopyroxene and garnet solid solutions enables extrapolation of experimentally determined equilibria in the MgSiO3-Al2O3 system to uninvestigated parts of pressure-temperature-composition space. Apparent discrepancies in the experimental data for simple and multicomponent systems may be explained by considering the effect of CaO and FeO on reducing pyrope activity in the garnet solid solutions. Equilibration pressures of natural garnet-orthopyroxene assemblages may be calculated, provided temperatures are known, from a combination of the experimental data on the MgSiO3-Al2O3 system and analyses of coexisting natural phases. Despite the presence of a compositional gap in the system, the solubility of enstatite in diopside coexisting with orthopyroxene can also be approximately treated by an ideal solution model. An empirical approach has been developed to take account of Fe2+ on the orthopyroxene-clinopyroxene miscibility gap in natural systems in order to calculate equilibration temperatures of 2-pyroxene assemblages. The model presented reproduces almost all of the available experimental data for multicomponent systems to within 60° C.

Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationships in simple and complex systems

Condensation in the primitive solar nebula

The co-existing microphenocrysts of magnetite and ilmenite together with the ferromagnesian silicates in salic volcanic rocks have been analysed with the electron microprobe. The temperatures and oxygen fugacities of the oxide equilibration have been estimated from the curves of Buddington and Lindsley (1965). The co-existing ferromagnesian silicate phenocrysts are either iron-rich olivine, or orthopyroxene or biotite and amphibole; for each of these groups of phenocrysts, the oxide equilibration data are specific and fall on three distinct curves, parallel to experimental oxygen buffer curves. Many of the investigated rhyolites were quenched at temperatures near 900°C, which may represent liquidus temperatures for those with sparse phenocrysts, and also the intrusion temperature of water-undersaturated granites. The composition of the biotite phenocrysts, which are Al-poor and Ti-rich, taken in conjunction with the oxide data, suggest that two Lassen dacites precipitated biotite at a water fugacity of approximately 400 bars. The composition of the later crystallizing ferromagnesian silicates, particularly the pyroxenes which show a wide range in Fe/Mg ratio, is strongly influenced by the prior crystallization of the oxide phases. If the biotite phenocrysts are typical of acid liquids, then they are incapable of generating by fractionation a peraluminous residual liquid; rather they would tend to make a liquid peralkaline.

The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesian silicates

Publisher Summary This chapter focuses on measurements and theories pertaining to homogeneous nucleation under cooled liquids and glasses that transform to phases of the same composition. The dynamical model describing the cluster evolution appears to be quantitatively correct. Although there are some experimental and theoretical difficulties with the classical theory, there are also many approaches to rectify these problems. At present, there are no experiments that can demonstrate or can refute conclusively the validity of the classical theory in the regime where it is expected to be valid. This is partially because of a lack of knowledge of the correct values for the parameters that are fit by the theory. Better measurements of the steady-state and time-dependent nucleation rates and the free-energy difference as a function of temperature, and the design of new experiments such as the multistep annealing treatments discussed in the chapter are used to test more rigorously nucleation theories. Time-dependent nucleation and the interface kinetics are incorporated into the field-theoretic approaches to give theories that are as widely applicable and, hence, testable as the classical theory.

Crystal Nucleation in Liquids and Glasses

Phase equilibrium relations in the liquidus temperature region of the system CaO-iron oxide-SiO2 in air were determined, using the quenching technique. The results are illustrated by means of a projection of the liquidus surface onto the composition triangle CaO-Fe2O3-SiO2. A supplementary diagram is presented in order to indicate true compositions of liquids at liquidus temperatures. Data obtained in the present investigation are combined with literature data to construct diagrams showing stability relations among crystalline phases at subsolidus temperatures. A diagram is also presented to show phase relations along the join CaO SiO2-2CaO Fe2O3.

Phase Equilibria in the System CaO‐Iron Oxide‐SiO2, in Air

Phase equilibria in the system CaO-cobalt oxide in air

Equilibrium phase compositions and thermodynamic properties of olivines and pyroxenes in the system MgO-“FeO”SiO2

Phase equilibrium data, obtained by the quenching technique, are presented for mixtures in the iron oxide-rich part of the system CaO-iron oxide in air and at 1 atm. O2 pressure. Present data are combined with data available in the literature to construct phase diagrams comprising the region from liquidus temperatures to temperatures slightly below the solidus.

Arnulf Muan

Papers

Phase Equilibria in the System CaO‐Iron Oxide‐SiO2, in Air

Phase equilibria in the system CaO-cobalt oxide in air

Equilibrium phase compositions and thermodynamic properties of olivines and pyroxenes in the system MgO-“FeO”SiO2

Phase Equilibria in the System CaO-Iron Oxide in Air and at 1 Atm. O2 Pressure

Phase Equilibrium Studies in the System Iron Oxide- A12O3 in Air and at 1 Atm. O2 Pressure