The Rotation of Sunspots During Activity Cycle 22

The solar rotation rate derived from the measurements of daily sunspot positions during activity cycle 22 (1988–1996) are presented. The averaged differential rotation is nearly symmetric with respect to the equator. The comparisons of our measurement with those for previous cycles show that the equatorial rotation rate gradually increases from cycle 18 to 22.     

Thermal expansion of single-crystal tephroite

The thermal expansion of tephroite (Mn₂SiO₄) at temperatures between 25 and 850°C has been determined by a dilatometric technique. The analysis of data in terms of Grüneisen's theory yields the Grüneisen's parameter γ=1.04, and the pressure derivative of rigidity (?G/?P)=0.7.     

The effect of sulfur content on density of the liquid Fe–S at high pressure

The density of liquid Fe–S was measured at 4 GPa and 1,923 K using a sink/float method with a composite density marker. The density marker consisted of a Pt rod core and an Al₂O₃ tube surrounding. The uncertainty in the density of the composite marker is much smaller than that of the composite sphere, which had been used in previous density measurements. The density of liquid Fe–S decreases nonlinearly with increasing sulfur content at 4 GPa and 1,923 K. This tendency is consistent with the results measured at ambient pressure. The molar volume of FeS calculated from the measured density gradually increases with sulfur content. The excess molar volume from ideal mixing of Fe and S at 4 GPa was negative value. The new method proposed here is applicable to the density measurement of other Fe alloys at high pressure. The tendency of the molar volume and the excess molar volume with sulfur content at ambient pressure is consistent with these at high pressure at least up to 4 GPa. The excess molar volume at high pressure is essential for estimating the amount of light elements in the outer core.     

Petrology and CHIME geochronology of Pan-African high K and Sr/Y granitoids in the Nkambe area, Cameroon

The Central African Belt in the Nkambe area, northwestern Cameroon represents a collisional zone between the Saharan metacraton and the Congo craton during the Pan-African orogeny, and exposes a variety of granitoids including foliated and massive biotite monzogranites in syn- and post-kinematic settings. Foliated and massive biotite monzogranites have almost identical high-K calc-alkaline compositions, with 73–67 wt.% SiO₂, 17–13 wt.% Al₂O₃, 2.1–0.9 wt.% CaO, 4.4–2.7 wt.% Na₂O and 6.3–4.4 wt.% K₂O. High concentrations of Rb (264–96 ppm), Sr (976–117 ppm), Ba (3680–490 ppm) and Zr (494–99 ppm), with low concentrations of Y (mostly< 20 ppm with a range 54–6) and Nb (up to 24 ppm) suggest that the monzogranites intruded in collisional and post-collisional settings. The Sr/Y ratio ranges from 25 to 89. K, Rb and Ba resided in a single major phase such as K-feldspar in the source. Garnet was present in the source and remained as restite at the site of magma generation. This high K₂O and Sr/Y granitic magma was generated by partial melting of a granitic protolith under high-pressure and H₂O undersaturated conditions where garnet coexists with K-feldspar, albitic plagioclase. CHIME (chemical Th–U-total Pb isochron method) dating of zircon yields ages of 569 ± 12–558 ± 24 Ma for the foliated biotite monzogranite and 533 ± 12–524 ± 28 Ma for the massive biotite monzogranite indicating that the collision forming the Central African Belt continued in to Ediacaran (ca 560 Ma).     

Contrasting ages between isotopic chronometers in granulites: monazite dating and metamorphism in the Higo Complex, Japan

The Higo Complex of west-central Kyushu, western Japan is a 25 km long body of metasedimentary and metabasic lithologies that increase in metamorphic grade from schist in the north to migmatitic granulite in the south, where granitoids are emplaced along the southern margin. The timing of granulite metamorphism has been extensively investigated and debated. Previously published Sm–Nd mineral isochrons for garnet-bearing metapelite yielded ca.220–280 Ma ages, suggesting high-grade equilibration older than the lower grade schist to the north, which yielded ca.180 Ma K–Ar muscovite ages. Ion and electron microprobe analyses on zircon have yielded detrital grains with rim ages of ca.250 Ma and ca.110 Ma. Electron microprobe ages from monazite and xenotime are consistently 110–130 Ma. Two models have been proposed: 1) high-grade metamorphism and tectonism at ca.115 Ma, with older ages attributed to inheritance; and 2) high-grade metamorphism at ca.250 Ma, with resetting of isotopic systems by contact metamorphism at ca.105 Ma during the intrusion of granodiorite. These models are evaluated through petrographic investigation and electron microprobe Th–U–total Pb dating of monazite in metapelitic migmatites and associated lithologies. In-situ investigation of monazite reveals growth and dissolution features associated with prograde and retrograde stages of progressive metamorphism and deformation. Monazite Th–U–Pb isochrons from metapelite, diatexite and late-deformational felsic dykes consistently yield ca.110–120 Ma ages. Earlier and later stages of monazite growth cannot be temporally resolved. The preservation of petrogenetic relationships, coupled with the low diffusion rate of Pb at < 900 °C in monazite, is strong evidence for timing high-temperature metamorphism and deformation at ca.115 Ma. Older ages from a variety of chronometers are attributed to isotopic disequilibrium between mineral phases and the preservation of inherited and detrital age components. Tentative support is given to tectonic models that correlate the Higo terrane with exotic terranes between the Inner and Outer tectonic Zones of southwest Japan, possibly derived from the active continental margin of the South China Block. These terranes were dismembered and translated northeastwards by transcurrent shearing and faulting from the beginning to the end of the Cretaceous Period.     

Constraining tephra dispersion and deposition from three subplinian explosions in 2011 at Shinmoedake volcano,Kyushu, Japan

Constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge, because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real-time observations. Three andesitic subplinian explosions in January 2011 at Shinmoedake volcano, Japan, are used as a case study to validate selected empirical and theoretical models using observations and field data. Tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass/area. A new cubic B-spline interpolation method is also examined. Magma discharge rate is estimated using theoretical plume models incorporating the effect of wind. Results are consistent with observed plume heights (6.4–7.3 km above the vent) and eruption durations. Estimated tephra volumes were 15–34?×?10⁶ m³ for explosions on the afternoon of 26 January and morning of 27 January, and 5.0–7.6?×?10⁶ m³ for the afternoon of 27 January; magma discharge rates were in the range 1–2?×?10⁶ kg/s for all three explosions. Clast dispersal models estimated plume height at 7.1?±?1 km above the vent for each explosion. The three subplinian explosions occurred with approximately 12-h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations.     

Sedimentological features of Cretaceous--Tertiary (K/T) boundary section along Heilongjiang River,Northeast China

The Jiayin area along the Heilongjiang River in Northeast China has attracted stratigraphic and sedimentological interests recently because the Cretaceous--Tertiary (K/T) boundary should be located in this non-marine succession.Dinosaur remains disappear suddenly at the upper part of the Maastrichtian,whereas plants gradually evolved throughout the succession.Analysis of sedimentary facies has been carried out and paleo-environments through Upper Cretaceous to lower Paleocene sections are reconstructed.Fluvial to lacustrine sedimentary environments are inferred from the facies.Several debris flow events have been identified,and it is in these deposits that the dinosaur fossils are concentrated.     

Depositional Age of a Fossil Whale Bone from São Paulo Ridge,South Atlantic Ocean,Based on Os Isotope Stratigraphy of a Ferromanganese Crust

Whale carcasses (whale falls) deposited on the deep seafloor are associated with a distinctive biotic community. A fossil whale bone recovered from São Paulo Ridge, South Atlantic Ocean, during cruise YK13–04 Leg 1 of R/V Yokosuka was covered by a ferromanganese (Fe–Mn) crust approximately 9 mm thick. Here, we report an age constraint for this fossil bone on the basis of Os isotopic stratigraphy (¹⁸⁷Os/¹⁸⁸Os ratio) of the Fe–Mn crust. Major‐ and trace‐element compositions of the crust are similar to those of Fe–Mn crusts of predominantly hydrogenous origin. Rare earth element concentrations in samples of the crust, normalized with respect to Post‐Archean average Australian Shale, exhibit flat patterns with positive Ce and negative Y anomalies. These results indicate that the Fe–Mn crust consists predominantly of hydrogenous components and that it preserves the Os isotope composition of seawater at the time of its deposition. ¹⁸⁷Os/¹⁸⁸Os ratios of three Fe–Mn crust samples increased from 0.904 to 1.068 in ascending stratigraphic order. The value of 1.068 from the surface slice (0–3 mm depth in the crust) was identical to that of present‐day seawater within error (~1.06). The value of 0.904 from the basal slice (6–9 mm) equaled seawater values from ca. 4–5 Ma. Because it is unknown how long the bone lay on the seafloor before the Fe–Mn crust was deposited, the Os stratigraphic age of ca. 5 Ma is a minimum age of the fossil. This is the first application, to our knowledge, of marine Os isotope stratigraphy for determining the age of a fossil whale bone. Such data may offer valuable insights into the evolution of the whale‐fall biotic community.