An improved chemical separation method for Hf isotope ratio measurement using both the thermal ionization mass spectrometer (TIMS) and the multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) is presented in this paper. In the first column (2.5-ml Eichrom Ln-spec resin), Hf cut was collected with 2M HCl-0.2M HF after washing the major elements, HREE, Ti, Nb, and Zr. For further Hf purification, the second column (1-ml Ln-spec resin) chemistry was conducted in a manner similar to that of the first column. The first column is designed for treatment with a 0.5-g silicate rock sample for TIMS analysis. Thus, because the Hf amount required for MC-ICP-MS analysis is much lesser than that required for TIMS analysis, the column chemistry for MC-ICP-MS analysis can be scaled down, depending on the amount of digested sample. Although there is a need to improve the TIMS technique, the TIMS Hf data obtained for geological reference rocks and Ethiopian flood basalts after the application of the proposed separation methods are consistent, within analytical error, with the previously reported data obtained using the MC-ICP-MS. The advantages of the proposed method include a reduction in the amount of reagents used (hence, a consequent reduction in the blank contribution), reduction in the time required, and a simplified preparation requiring a fewer number of acids.
The crystal structure of anhydrous phase X with composition K1.93(Mg2.02Cr0.02)Si2.00O7 was refined by means of X-ray diffraction analysis of a single-crystal synthesized at 16.5 GPa and 1700 °C. The structure is trigonal with space group P31m and the cell parameters are a = 5.0756 (1), c = 6.5969 (2) Å, and V = 147.179 (6) Å3. The structure is closely related to those of the space group P63cm, which have previously been identified to have hydrous and anhydrous phase X's. However, these differ in the arrangements of Si2O7 groups and MgO6 octahedra.
Many thin mafic dykes occur within and around the Cretaceous Hiei Granite pluton in southwest Japan. Petrographically, these dykes are spessartite, basalt, and dolerite. Petrographical and geochemical characteristics indicate their designations as calc-alkaline basalt and basaltic andesite. Their magmas have probably originated in the LILE-rich mantle wedge under the Eurasian continental margin matured arc. These mafic rocks are crystallized and have suffered successive hydrothermal alteration under high vapor condition. Among the Cretaceous granites around Lake Biwa, the older ones of ∼ 95 Ma, such as the Hiei and Kaizuki-yama plutons, are accompanied exclusively by these mafic dykes including spessartite; however, the younger (∼ 70 Ma) ones are never accompanied by these dykes.
The GSJ B326 borehole was drilled in the Joban coastal region, east of the Abukuma Plateau, reached a depth of ∼ 1005 m. Although most of the sequence is composed of Tertiary sediments, plutonic rocks occur from 815.1 m to 1005 m in depth. The lithology of the plutonic rocks is tonalite and subordinate aplite veins. Radiometric ages of zircons in three granitoids were obtained from the 238U/206Pb ratio and isotopic compositions of Pb using a Sensitive High Resolution Ion MicroProbe (SHRIMP II). The weighted mean of the zircon ages of a sample from the shallower part of the borehole is 293 ± 1.8 Ma, whereas that for two samples from the deeper part of the borehole is 300.3 ± 1.5 Ma and 304.3 ± 1.7 Ma. The previously reported U-Th-Pb chemical age of uraninite from the deeper part of the borehole is 285 ± 4 Ma. These data indicate that a melt intruded into the ∼ 300 Ma rock body at ∼ 290 Ma. Granitoid with 300 Ma are scarce in the Japanese Islands, and this is the first report of such granitoids in northeast Japan.
Kyanite and andalusite are newly found in migmatized pelitic granulites from the Kerala Khondalite Belt, Southern India. Anhedral tiny grains of kyanite included within altered cordierite were interpreted as possible remnants of prograde metamorphism of the granulites within the kyanite stability field. Andalusite shows two distinct modes of occurrence; some are of magmatic origin and others are formed as partial replacement products of alkali-feldspar and plagioclase mainly in leucosomes. Our data put new constraints not only on the P-T path followed by the granulites but also on the correlation between the Gondwana fragments. The Kerala Khondalite Belt is closely correlated with the Southwestern Group (southwestern part of the Highland Complex) in Sri Lanka.
Datasets obtained by viscometry of Fuji 1707 basalt at a pressure of one atmosphere (Ishibashi, 2009) were analyzed by using the Bingham fluid model, and both the yield stress (τy) and Bingham viscosity (ηB) were determined. The relation between ηB and the crystallinity (Φ) was compared with the Krieger-Dougherty equation, and both the maximum packing fraction of crystals (Φm) and intrinsic viscosity (ν) for Bingham viscosity were determined as Φm = ∼ 0.45 and ν = ∼ 5.25, respectively; thus, it was found that Φm decreased and ν increased concomitantly with an increase in the shape anisotropy of crystals. However, the obtained value of νΦm (∼ 2.36) was similar to that in the case of uniform, isotropic particles (2.5). This indicates that the effect of crystal shape anisotropy on ηB might be predicted only on the basis of a change in Φm. For Φ > 0.133, τy was found to be finite; it increased with Φ, which suggests that the critical crystallinity for the onset of yield stress, Φc, is at least lower than 0.133. The upper limit of Φc is close to the value calculated numerically for randomly oriented uniform particles by Saar et al. (2001) (their value is 0.10-0.15 for a width/length (W/L) ratio of 0.1 to 0.2, which is similar to the ratios in the case of basalt).
Mn-bearing lawsonite was discovered in meta-siliceous rocks metamorphosed under the lawsonite-blueschist facies formed at less than 350 °C and 0.8-1.0 GPa in the Hakoishi serpentinite mélange of the Kurosegawa Belt, Central Kyushu, Japan. The lawsonite deposits were accompanied by those of hematite, braunite (Mn2+Mn63+SiO12), and quartz, indicating that the rock had metamorphosed under high Oxygen fugacity (fO2) (∼ -20 < log fO2 < -5) at the abovementioned P-T conditions. The Oxygen fugacity led to the conversion of all the iron into ferric compounds and some of the manganese into its trivalent form. As a result, the lawsonite was found to contain a significant amount of (Mn3+ + Fe3+), substituting ∼ 5-11 mol% of Al in the ideal lawsonite formula. Lawsonite in meta-siliceous rocks metamorphosed under low fO2 state (∼ log fO2 < -20), and metabasites collected from the same mélange contained lesser amount of (Mn3+ + Fe3+), substituting ∼ 3-5 mol%. The amount of Sr and Ba in the analyzed lawsonite were below the detection limit of energy-dispersive microprobe analysis, ∼ <0.1 wt%. This indicated the existence of an unknown endmember of the lawsonite group of minerals, CaFe23+Si2O7(OH)2·H2O or CaMn23+Si2O7(OH)2·H2O on the basis of the observed substitution. The extremely high fO2 state that results in the conversion of all the iron into ferric compounds along with the Mn-rich local chemical compositions would necessarily enhance (Mn3+ + Fe3+) ⇔ Al substitution in lawsonite.
Ultramafic xenoliths from Kurose, Southwest Japan, are fragments of the lithospheric mantle beneath the back arc of the active Southwest Japan volcano-tectonic arc. Trace element and Sr-Nd isotopic compositions of the clinopyroxenes in the ultramafic xenoliths suggest that several enrichment processes are responsible for the geochemical variation. These xenoliths would have witnessed the following events: (1) open-system partial melting of the continental lithosphere with an influx of an asthenospheric melt with MORB-like isotopic composition during the formation of the back-arc basin that resulted from the Japan Sea opening, (2) open-system melting under an influx of a fluid/melt derived from a subducted slab, and (3) metasomatism after these partial melting events by an island arc tholeiitic basalt melt in the Neogene period. Moreover, variations in the depletion levels of Zr and Ti in the clinopyroxenes suggest that source depletion preceded the melting and metasomatic events.