Titanian andradite and hydroandradite containing up to ~ 10 wt% TiO2 were identified in rodingite as well as the host serpentinite in a sample obtained from the Nomo unit, Nagasaki Metamorphic Rocks (western Kyushu, Japan), representing a Cretaceous subduction complex. The rodingite consists of garnet (solid solution among three end–member compositions: grossular, andradite, and titanian hydrogarnet), diopside and chlorite, along with minor amounts of perovskite, ilmenite, and titanite. This assemblage was formed by metasomatism under conditions of epidote–blueschist facies metamorphism at 0.6–0.8 GPa and ~ 400°C. X–ray single crystal diffraction and chemical analyses determined the formula Ca3.00(Fe3+0.64Ti4+0.24Mg0.03V0.02Sc0.01Al0.06)2(Si0.90Al0.03□0.07)3O11.35
(OH)0.65, in which Fe3+ preferentially occupies the Y–sites and Ti is solely in the tetravalent state. We propose a new type of coupled substitution, Fe3+ + H+ + □ = Ti4+ + □, in the titanian andradite, indicating that it does not belong to the solid solution in the andradite–morimotoite–schorlomite system of the International Mineralogical Association (IMA) classification scheme. The Fe ions are ferric (Fe2+ is estimated to be 3% or less), showing that the formation of the titanian andradite occurred under oxidizing conditions. In the reaction zone, the titanian andradite overgrowth on the ilmenite and the partial replacement of the perovskite by titanian andradite show the incorporation of TiO2 into the garnet via reaction with TiO2–bearing minerals under relatively oxidizing conditions. In addition, the presence of andradite coronas around the magnetite rim formed from the alteration of primary chromite provides evidence of Ti mobility in the serpentinite. These reaction relations highlight the titanian andradite formation process and allow us to propose associated reactions based on the singular value decomposition method.
CO2–containing melanophlogite from Fortunillo, Italy was studied using a micro–Raman spectrometer with the ability to measure the low–frequency region. A very intense and broad feature was found below 100 cm−1. To clarify the origin of this feature in relation with CO2, heat treatment experiments and in–situ high–temperature Raman measurements were conducted up to 1100 °C. As a result of the heat treatment experiments, nearly CO2–free melanophlogite was obtained at 950 °C for 6 h. For shorter time duration or lower treatment temperature, CO2 vibrational Raman peaks (Fermi diad) were still observed, and those peaks were split. The low–frequency feature also reduced its intensity in these degassed samples. For the in–situ study, the intensity of CO2 Raman peaks started to drop at around 450 °C, and simultaneously the low–frequency feature intensity decreased. The splitting of the CO2 Raman peaks started from 450 °C, and it was interpreted as redistribution of CO2 molecules in two distinct cages in the structure. The low–frequency feature completely disappeared at 1100 °C. It was concluded that the low–frequency feature is originated from CO2 molecules. Librational and translational modes of CO2 molecules in the cages of melanophlogite would be responsible for the low–frequency feature. The high–temperature Raman spectroscopic study thus provides us insight into CO2 diffusion in melanophlogite structure.
The electric field gradient (EFG) tensor of the 57Fe Mössbauer nucleus is a basic physical property that is important in Mössbauer spectra measurements of a single crystal because the EFG provides a constraint on the intensity of quadrupole splitting peaks. To reveal the EFG tensor of Fe3+ in the octahedral M1 site of clinopyroxene, Mössbauer spectra of six crystallographically oriented single crystal of aegirine in thin sections were measured. The asymmetric parameter (η) of the EFG tensor of aegirine was almost equal to 1. The principal axes of the EFG tensor of aegirine were almost oriented along the b × c, b, and c axes, and the Vxx component of the EFG was along the b axis. To compare the experimental results with theoretical EFGs, three EFG tensors due to ligand oxygen ions were calculated based on atomic positions determined by X–ray structural analysis. The calculated EFG tensors were not necessarily consistent with the experimentally determined EFG tensors. This indicates that experimental determination of EFG is necessary for single crystal Mössbauer measurements because the calculated EFG may be inaccurate.
T–prism is a Microsoft–Excel–based tool that visualizes ternary space diagrams (i.e., ternary prisms) in three–dimensional (3D) space. This tool allows us to examine the overall features of a dataset in both three– and two–dimensional spaces by altering the viewing angles. T–prism involves two algorithms that coordinate the transformation and rotation of diagrams in a virtual 3D space. This paper describes a new and simple coordinate transformation from a ternary space diagram (i.e., ternary prisms) to an XYZ orthogonal system. Coordinates of a point of interest in the ternary space diagram, expressed using the proportions of three components of a basal triangle (r, l, and t, where r + l + t = 100) and an additional variable (h), are converted into coordinates in the orthogonal system as follows: x = (r + 100 − l)/2, y = √3/2t, and z = fh. Here, f represents the correction factor used to appropriately express the length of an axis perpendicular to the basal ternary diagram. T–prism is particularly suitable for visualizing phase relations in multicomponent systems, the physical properties of materials, and compositional variations in solid solutions. Hence, the tool is applicable to a broad variety of research and teaching fields, including Earth science, material science, and physical chemistry.
Microthermometric data of fluid inclusions can elucidate the physicochemical properties of lithospheric fluids, but the inclusions must satisfy several criteria to yield proper fluid information. One is the ‘constant volume criterion’: the inclusion volume must remain constant after being trapped. However, volume changes of fluid inclusions occur in nature during emplacement underground or uplifting to the surface. They can also occur during sample preparation or data collection in the laboratory. Therefore, thermoelastic deformation of the crystal lattice surrounding fluid inclusions during experiments might increase uncertainty about microthermometric data. Herein, we introduce and assess a method using the equation of state of pure CO2 and thermoelastic equilibrium between a fluid inclusion and a host mineral to estimate fluid inclusion volume changes accurately during measurements of homogenization temperature. The estimation is valid if the inclusion and host are isotropically elastic, concentric spheres. Subsequently, we extended the equation of state to a more comprehensive Redlich and Kwong equation of state, which is applicable to more complicated fluid systems. Furthermore, for accurate treatment of the elastic effects involving an elastically anisotropic host mineral, we propose the method’s application to an anisotropic host mineral. If physical properties of the host mineral and the molar volume of the fluid inclusion at an arbitrary temperature are known, then one can use this method for accurate estimation of the molar volume at a given temperature. This microthermometric data based method can accurately elucidate characteristics of the crust and mantle–fluid activity.
The sound velocity and density of ε–FeOOH have been simultaneously measured up to 24 GPa at room temperature using an ultrasonic pulse–echo–overlap method and a Kawai–type multi–anvil apparatus at BL04B1 in SPring–8. In the experimental pressure range, the velocity of both the P– and S–waves of ε–FeOOH was ~ 15% lower than that of an isostructural phase δ–AlOOH. The pressure dependence of the determined adiabatic bulk modulus (KS) increased in the higher pressure range beyond 17 GPa, whereas that of the axial ratios a/c and b/c did not transition from negative to positive. A similar change of pressure dependence of KS was observed in δ–AlOOH, which is followed by a transition of proton distribution state to disordered, but the axial ratios of ε–FeOOH indicate that the transition would not occur up to 24 GPa.