Leucite-sodic plagioclase and melilite-plagioclase do not coexist in natural rocks. However, leucite and calcium-rich plagioclase may remain in equilibrium in alkaline silica-deficient rocks. The join leucite-akermanite-albite studied at atmospheric pressure is characterized by two four-phase points: one point occurs at leucite31akermanite47albite22 and 1275 °C, where leucitess, melilitess and diopsidess coexist in equilibrium with liquid, and the other point occurs at leucite38akermanite22albite40 and 1250 °C, where diopsidess, alkali feldspar, leucitess and liquid are in equilibrium. In the case of the join leucite-akermanite-albite50anorthite50 investigated at atmospheric pressure, there are two four-phase points: one point occurs at leucite14akermanite48(albite50anorthite50)38 and 1260 °C, where melilitess, leucitess, diopsidess and liquid coexist in equilibrium, and the other point occurs at leucite15akermantite35(albite50anorthite50)50 and 1240 °C, where diopsidess, leucitess and calcium-rich plagioclase are in equilibrium with liquid. When the join leucite-akermanite-albite50anorthite50 was studied at 1 GPa (in H2O-saturated conditions) to determine the effect of pressure, it was noted that the field of melilitess completely disappears, and this join is characterized by a single four-phase point occurring at leucite43akermanite22(albite50anorthite50)35 and 1060 °C, where diopsidess, calcium-rich plagioclase, and leucitess are in equilibrium with liquid. The present study indicates that: 1) leucite and sodic plagioclase do not coexist in equilibrium. When leucite is in equilibrium with feldspar, it is alkali feldspar having the compositional range, An3-4Ab50-53Or45-47. 2) In the presence of leucite, akermanite and albite react to form diopsidess, nepheliness, wollastonitess, and alkali feldspar. 3) In the join leucite-akermanite-albite50anorthite50, plagioclase coexisting with leucite has the compositional range, An60-66Ab17-26Or12-17. 4) In the join leucite-akermanite-albite50anorthite50 studied at 1 GPa (in H2O-saturated conditions), melilite is completely eliminated.
Geochemical and isotopic data are presented for Bure volcanic rocks from the northwestern Ethiopian plateau to investigate the processes involved in the genesis of the erupted magma and the nature of mantle source compositions during plume-induced continental rifting. The Bure area is mainly composed of flood basalts (30-25 Ma), ranging from transitional tholeiite to alkaline basalts, with a probable Quaternary alkaline basalt single lava flow, scoria cones and trachyte plugs. The transitional tholeiites have variable incompatible elements and isotopic ratios (87Sr/86Sr = 0.70329-0.70429, 143Nd/144Nd = 0.51281-0.51304 and 206Pb/204Pb = 18.36-19.08). In contrast, the alkaline basalts display a homogeneous incompatible element and Sr-Nd isotopic ratios (87Sr/86Sr = 0.70311-0.70363 and 143Nd/144Nd = 0.51279-0.51288) with a wide range of Pb isotopes (206Pb/204Pb = 18.91-19.83). Isotope and trace element variations within the Bure lavas reflect the involvement of: 1) an intrinsic isotopically depleted plume component, 2) a plume component having radiogenic Pb isotope and 3) an enriched crustal component. The first and third components played a significant contribution in the initial stage of plume-induced continental flood basalt magmatism.
Ferric iron and aluminum partitioning between MgSiO3-dominant perovskite (Mg-Pv) and CaSiO3-dominant perovskite (Ca-Pv) was investigated at 27-100 GPa and 1600-2500 K under oxidizing conditions using a starting composition of 0.85CaMgSi2O6 + 0.15Fe3+AlO3 employing a combined laser-heated diamond anvil cell, synchrotron radiation, and analytical transmission electron microscopy. The product phases were Mg-Pv, Ca-Pv, and a small amount of stishovite at pressures below 30 GPa, while a two-phase assemblage of Mg-Pv and Ca-Pv was identified at pressures above 30 GPa. The appearance of stishovite below 30 GPa indicates the partial formation of an oxygen-deficient perovskite from 2ASiO3 + Fe3+AlO3 = 2AFe3+0.5Al0.5O2.5 (oxygen-deficient perovskite) + 2SiO2 (stishovite), where A = Mg or Ca. The composition of Mg-Pv and Ca-Pv show that ferric iron and aluminum were predominantly incorporated into Mg-Pv under oxidizing conditions, indicating that Mg-Pv is the dominant host phase for ferric iron and aluminum even under highly oxidizing lower mantle conditions.
A semi-automatic system for the chemical separation of Sr and Nd isotope analyses is proposed to attain efficient element separation. The system consists of a peristaltic pump and open column. Using the peristaltic pump, the sample solution and eluant are automatically drawn up from a test tube and loaded onto the resin bed in the column. The flow rate of the pump is adjusted according to the column and resin conditions. We measured the Sr and Nd isotopic ratios of samples JB-2 and JA-3 prepared using the proposed technique; the results are in good agreement with previously reported values. The proposed system reduces the required analysis time, and, unlike other automated systems, is applicable for any type of open column, resin, and geological material. The system has the added benefit of not requiring expensive additional instrumentation.
Changes in the absorption intensity (absorbance) at 254 nm of a fulvic acid solution in the presence of goethite powder were monitored in situ in a liquid cell at a temperature of 80 °C in a UV-visible spectrometer. The absorbance at 254 nm decreased rapidly with time in the initial stage in the presence of goethite with a first-order rate constant of k1UV = 3 × 10-4 s-1, while in the absence of goethite, the absorbance at 254 nm decreased slowly with time, with a first-order rate constant of k0UV = 6 × 10-7 s-1. A hydrothermal vessel was connected to a long-path gas cell infrared spectrometer to monitor the volatile compounds formed on heating the fulvic acid at 80 °C. Carbon dioxide formed gradually over time from the fulvic acid solution in the absence of goethite (k0CO2 = 1.5 × 10-6 s-1). The formation of CO2 in the presence of goethite occurred via two first-order reactions. The initial first-order rate constant of CO2 formation from fulvic acid in the presence of goethite (k1CO2 = 3.2 × 10-4 s-1) had the same magnitude as the decrease in absorbance at 254 nm. The second rate constant of CO2 formation (k2CO2 = 1.8 × 10-6 s-1) had the same magnitude as CO2 formation in the absence of goethite. These results suggest that the formation of CO2 from the fulvic acid is greatly accelerated by the presence of goethite, possibly through the adsorption of the fulvic acid on the goethite surface with subsequent redox reactions occurring.
The crystal structure of a single crystal of synthetic Fe-bearing hydrous forsterite (Mg1.85Fe0.14Si0.99H0.06O4) synthesized at 13.5 GPa and 1400 °C has been investigated using X-ray diffractometry. The data show a site occupancy of 96(3)%Mg + 4(1)%Fe + 0(4)% at the M1 site and a site occupancy of 89(3)%Mg + 8(1)%Fe + 3(4)% at the M2 site, indicating that the cation vacancies at the octahedral M sites predominantly occur at the M2 site. The occupancy at the T site was 99.0%Si(fixed) + 0(1)%Fe + 1(1)%, indicating a small number of vacancies with no detectable Fe occupation. A comparison of the calculated bond distances and reported stretching frequencies of the polarized IR spectra shows that the most probable H atom locations are near to the edges of the MO6.
Carbonaceous matter (CM) with various modes of occurrence has been observed in quartz veins in the biotite zone of the Ryoke metamorphic belt in the Yanai district, Yamaguchi Prefecture, SW Japan. Raman spectroscopic analysis of the CM revealed that high temperature fluids had percolated through fractures, which were now occupied by the quartz veins that had formed during the retrograde stages of metamorphism. These fluids may have also affected the degree of organization of the fine-grained CM particles in the host pelitic rocks and the coarse-grained particles that had precipitated from them at a later stage.
The above PDF file shows errata of the paper entitled “Distribution of chromium among the octahedral sites in chromian epidote from Iratsu, central Shikoku, Japan" by Mariko NAGASHIMA, Masahide AKASAKA, Atsushi KYONO, Kuniaki MAKINO and Ko IKEDA (Vol. 102, no. 4, 240-254,2007)
Wrong:See PDF attached
Right:See PDF attached