This paper presents the temperature and pressure dependence of the minimum binary diffusivity in granitic melts. The minimum diffusivities are determined by monitoring the temporal development of the diffusion-controlled melt layer(DCM) in granitic systems (albite (Ab)-quartz (Qtz)-H2O and orthoclase (Or)-Qtz-H2O) gathered during 31 melting experiments under conditions of 800-900 °C and 100-200 MPa for durations of 19-72 h. The DCM is formed between single crystals (Ab or Or crystals) and powdered quartz in all runs and is characterized by a distinct concentration gradient. The maximum thickness of the DCM increases systematically with temperature, pressure, and run duration. Temporal development of the DCM obeys the parabolic growth rate law, using which the diffusivity can be estimated. Plots of concentrations along the diffusion paths in ternary diagrams (Na2O-Al2O3-SiO2 diagram for the Ab-Qtz-H2O system and K2O-Al2O3-SiO2 diagram for the Or-Qtz-H2O system) show linear trends rather than S-shaped trends, indicating that binary nature of diffusion occurs in these systems. Therefore, the diffusive component can be interpreted as an albite component or orthoclase and quartz components (SiO2) rather than an oxide or a cation.
A fully automated open-column resin-bed chemical-separation system, named COLUMNSPIDER, has been developed. The system consists of a programmable micropipetting robot that dispenses chemical reagents and sample solutions into an open-column resin bed for elemental separation. After the initial set up of resin columns, chemical reagents, and beakers for the separated chemical components, all separation procedures are automated. As many as ten samples can be eluted in parallel in a single automated run. Many separation procedures, such as radiogenic isotope ratio analyses for Sr and Nd, involve the use of multiple column separations with different resin columns, chemical reagents, and beakers of various volumes. COLUMNSPIDER completes these separations using multiple runs. Programmable functions, including the positioning of the micropipetter, reagent volume, and elution time, enable flexible operation. Optimized movements for solution take-up and high-efficiency column flushing allow the system to perform as precisely as when carried out manually by a skilled operator. Procedural blanks, examined for COLUMNSPIDER separations of Sr, Nd, and Pb, are low and negligible. The measured Sr, Nd, and Pb isotope ratios for JB-2 and Nd isotope ratios for JB-3 and BCR-2 rock standards all fall within the ranges reported previously in high-accuracy analyses. COLUMNSPIDER is a versatile tool for the efficient elemental separation of igneous rock samples, a process that is both labor intensive and time consuming.
Quartz dissolves in Na+ solutions much faster than in pure water though the experimental activation energies are essentially the same. To elucidate the mechanism, silica dissolution was simulated using Gaussian 03 software at B3LYP/3-21G* initially and the B3LYP/6-311G(2d,p) levels, applied to a modeled silica Si4O6(OH)4 in the presence of an NaOH molecule and up to five water molecules. Each water molecule was added one by one to the system and approached the surface silicon in successive geometry optimizations. The atomic positions of the sodium hydroxide, the water molecules and the surface SiO3(OH) moiety were varied to mimic the surface reaction whereas the positions of the remaining Si3O3(OH)3 atoms were frozen to represent the bulk structure throughout the geometry optimization. In the first step a single H2O molecule was added to the system [Si4O6(OH)4 + NaOH]. None of the Si-O bonded interactions were ruptured by the intrusion of the water molecule but the surface Si was stabilized in the Q3Si site (connected to three Si-O-Si bridges), being coordinated by five oxygen atoms. The energy barrier was 63 kJ/mol. In each of the second and third steps one more water molecule was introduced to the system. One Si-O bonded interaction of the Si-O-Si bridges was ruptured to make Q2Si and Q1Si sites in the second and third steps, respectively, and the energy barriers were low (22-29 kJ/mol). In the fourth and fifth steps, the added water molecules were prevented by the sodium ion from reaching the last Si-O-Si bridge, leaving the Si in the Q1Si site. The basis set was raised to the 6-311G(2d,p) level and applied to the 63 kJ/mol barrier found in the first step to determine the maximum energy barrier in the series of reactions. The barrier increased to 88 kJ/mol (82 kJ/mol in enthalpy), which is still in the range of experimental activation energies of 46-96 kJ/mol. In summary sodium works to stabilize the surface silicon in penta-coordination with the energy barrier, 82 kJ/mol, resulting in longer Si-O distances and the weakening of the bonded interactions. This makes the Si-O rupture easier and faster, which gives insight as to how the presence of alkali enhances silica dissolution.
Common occurrence of prehnite and pumpellyite is newly identified from metabasites of Tobiishi sub-unit in the Kurosegawa belt, Yatsushiro area, Kyushu, where Ueta (1961) had mapped as a greenschist facies area. Prehnite and pumpellyite are closely associated with chlorite, calcite and quartz, and they mainly occur in white colored veins or in amygdules in metabasites of the relevant area, but actinolite and epidote are rare in them. Pumpellyite is characterized by iron-rich composition (7.2-20.0 wt% as total iron as FeO) and its range almost overlaps with those in prehnite-pumpellyite facies metabasites of Ishizuka (1991). These facts suggest that the metabasites of the Tobiishi sub-unit suffered the prehnite-pumpellyite facies metamorphism, instead of the greenschist facies.
A field-emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectrometer (EDS) detector of a superconducting transition-edge sensor (TES) microcalorimeter is a new system for electron-microprobe chemical analyses. FE-SEM with TES was used for qualitative and semi-quantitative analyses of rare-earth elements (REE) at a low accelerating voltage of 5 kV. Four characteristic M-lines were detected in the LaB6 spectrum: LaMζ at 640, LaMαβ at 841, LaMγ at 1021, and a weak line (M2N4 transition) at 1100 eV. The spectra of other rare-earth borides, rare-earth phosphates, and monazite were assigned in the same way as the La M-lines were. For quantitative analyses, we used a calibration curve method, using standard specimens of known chemical compositions. Linear calibration curves for plots of P, Ca, La, Ce, Pr, and Nd intensities versus each weight percentage were obtained. Semi-quantitative analyses of rare-earth minerals should be carried out at low accelerating voltages using a calibration curve method. In a TES-EDS system, a low accelerating voltage can be used to improve the spatial resolution, without the sensitivity disadvantages of low-energy X-ray emissions. Moreover, a strong increase in the Mαβ intensity with increasing atomic number Z was seen, so the detection limits of heavy REE was much lower than those of light REEs. These results suggest that the TES-EDS system could be a useful analytical tool in rare-earth mineralogy.
Rhabdophane-(Y), ideal formulaYPO4·H2O, occurs in a druse of the Higashimatsuura basalt at Hinodematsu, Genkai-cho, Saga Prefecture, Japan. It occurs as short rod-like crystals and forms radial aggregates. Rhabdophane-(Y) is hexagonal, P6222, a = 6.959(2) Å, c = 6.384(2) Å, V = 267.7(1) Å3, Z = 3. It is yellowish white to yellowish brown in color with a silky to dull luster. The density is 4.54 g/cm3 (calc.). The strongest lines in the X-ray powder diffraction pattern are [d (I/I0) hkl] 2.821 (100) 102, 3.013 (77) 200, 6.026 (76) 100, 4.385 (47) 101, 3.480 (44) 110, 2.127 (28) 003, and 1.854 (26) 212.
To facilitate identification of high-pressure K-cymrite (KAlSi3O8·H2O) phase and its anhydrous form (kokchetavite) in natural rocks, we have synthesized both phases and have characterized them by micro-Raman and NMR spectroscopy. K-cymrite was synthesized at 5 GPa and 800 °C. Kokchetavite was obtained by dehydrating K-cymrite at ambient pressure and 550 °C. The 1H MAS and 1H-29Si CP MAS NMR spectra of K-cymrite are consistent with the reported crystal structure that contains H2O molecules and has a disordered Si-Al distribution. The Raman spectra obtained under ambient conditions for K-cymrite (and kokchetavite) contain major peaks at 114.0 (109.1), 380.2 (390.0) and 832.5 (835.8) cm-1. For K-cymrite, OH stretching vibration is also observed at 3541 cm-1 with a shoulder at 3623 cm-1. The Raman spectrum for kokchetavite is consistent with that previously reported for a natural sample found as inclusions in clinopyroxenes and garnets in a garnet-pyroxene rock. However, the data for K-cymrite are inconsistent with the Raman features of a previously reported “relict K-cymrite in K-feldspar” from an eclogite. Pressure- and temperature-dependencies of the Raman shifts for the strongest peak of both phases are also reported.
The following are errata for the original article entitled “Hydrous and anhydrous melting experiments of an alkali basalt and a transitional tholeiite from the Oginosen volcano, Southwest Japan: The possible influence of melt depolymerization on Ca-Na partitioning between plagioclase and the melt” by Ushio HONMA (Vol. 107, no. 1, 8-32, 2012).
Page 17, in the caption of Figure 3, line 4: 1 cm should be changed to read 1 mm.
Page 25, in the caption of Figure 5, line 5: 0.5 cm should be changed to read 0.5 mm.