Center to limb variation of the intensity of the photospheric faculae

Center to limb variation of the excess brightness of photospheric facular granules was observed at 530 nm with a balloon-borne telescope of 10 cm aperture. Facular granules are found to be 9.2% and 16.2% brighter than the adjacent quiet region at cos = 0.65 and 0.50 respectively, being the angle between the Sun's normal and the line of sight. This observation, together with our earlier result (Hirayama, 1978), leads to facular models which are 600 K hotter than the photosphere if the diameter of facular granules is assumed to be 600 km, and 1000 K hotter if 150 km is assumed instead. It was also found that the soft X-ray bright points as observed with the Skylab do not correspond spatially to the photospheric facular granules near the polar region.     

The assessment of weathering stages in granites using an EC/pH meter

The sidewall effects of a wind tunnel on aeolian sand transport were investigated experimentally. A wind tunnel was used to conduct the experiments with a given channel height of 120 cm and varying widths (B) of 40, 60, 80, 100 and 120 cm. Both vertical profiles of wind velocity and sand mass flux were measured at different locations across the test section. The results show that the wind velocity with saltation first increases and then decreases to a minimum, from the sidewall to the central line of the wind tunnel. The discrepancy among wind velocities at different locations of the transverse section decreases with decreasing tunnel width. The wind friction velocity across the wind tunnel floor, with the exception of the region closest to the sidewalls, does not deviate strongly in wide wind tunnels from that along the central line, whereas it does vary in narrow tunnels. The sand mass fluxes, with the exception of some near-bed regions, are larger along the central line of the wind tunnel than they are at the quarter width location from the sidewall. Unlikely previously reported results, the dimensionless sand transport rate, Qg / (ρu³) (where Q is the total sand transport rate, g is the gravitational acceleration constant, ρ is the air density, and u is the wind friction velocity), first decreases and then increases with the dimensionless friction velocity, u / u_t (where u_t is the threshold friction velocity). The above differences may be attributed to the sidewall effects of the wind tunnel. A dimensionless parameter, F_B = u / (gB)^1/2, is defined to reflect the sidewall effects on aeolian sand transport. The flows with F_B of 0.33 or less may be free from the sidewall effects of the wind tunnel and can ensure accurate saltation tunnel simulation.     

A neutron activation analysis of iridium concentration in Yamato carbonaceous chondrite

Iridium concentration in extra-terrestrial bodies is an important quantity in relation to Ir-rich geological layers. Ir concentration of a Yamato carbonaceous chondrite (Y-793321) has been measured by a neutron activation method. The measurement yields a value (0.57 ± 0.06) g per gramme for the chondrite.     

Advanced Micro-XRF Method to Separate Sedimentary Rhythms and Event Layers in Sediments: Its Application to Lacustrine Sediment from Lake Suigetsu,Japan

Event-related sedimentary layers, which are deposited occasionally due to volcanic eruptions, earthquakes or heavy rains, are often contained in the rhythmical sequences of lacustrine and marine sediments. We have developed an analytical method for separating the sedimentary rhythms and the event layers identified using the scanning X-ray analytical microscope (SXAM) and obtained sequential profiles of seven elements Al, Si, K, Ca, Ti, Mn, and Fe in the lacustrine sediment from Lake Suigetsu, Japan. Two types of event layers could be detected from the elemental composition of 33 layers of sediment: three known volcanic ash layers and 30 clay layers containing 12 turbidites. The recurrence interval of the latter, which may potentially be initiated and archived by locally important earthquakes, is estimated to be an average of 640 ± 160 years by using Sompi event analysis (SEA) based on an autoregressive (AR) model. After removing those portions that represented event layers from the elemental profiles, we obtained event-removed (ER) temporal profiles based on the tephrochronology of the three volcanic ash layers. The ER temporal profiles of manganese and iron, probably representing the siderite content, showed a millennial-scale variation in the Holocene that corresponded well with ice-rafting events in the North Atlantic.     

Rare Earth Element Enrichment in Late Archean Manganese Deposits from the Iron Ore Group,East India

The major, trace and rare earth element (REE) composition of Late Archean manganese, ferromanganese and iron ores from the Iron Ore Group (IOG) in Orissa, east India, was examined. Manganese deposits, occurring above the iron formations of the IOG, display massive, rhythmically laminated or botryoidal textures. The ores are composed primarily of iron and manganese, and are low in other major and trace elements such as SiO₂, Al₂O₃, P₂O₅ and Zr. The total REE concentration is as high as 975 ppm in manganese ores, whereas concentrations as high as 345 ppm and 211 ppm are found in ferromanganese and iron ores, respectively. Heavy REE (HREE) enrichments, negative Ce anomalies and positive Eu anomalies were observed in post‐Archean average shale (PAAS)‐normalized REE patterns of the IOG manganese and ferromanganese ores. The stratiform or stratabound shapes of ore bodies within the shale horizon, and REE geochemistry, suggest that the manganese and ferromanganese ores of the IOG were formed by iron and/or manganese precipitation from a submarine, hydrothermal solution under oxic conditions that occurred as a result of mixing with oxic seawater. While HREE concentrations in the Late Archean manganese and ferromanganese ores in the IOG are slightly less than those of the Phanerozoic ferromanganese ores in Japan, HREE resources in the IOG manganese deposits appear to be two orders of magnitude higher because of the large size of the deposits. Although a reliable, economic concentration technique for HREE from manganese and ferromanganese ores has not yet been developed, those ores could be an important future source of HREE.     

Mass motions due to shock propagations along low-lying loops in the solar atmosphere

The formation of fibrils in low-lying loops is investigated by performing one-dimensional nonlinear hydrodynamic calculations. The loops have the height of 3000–5000 km and have an atmosphere extending from the photosphere to the corona. A shock wave is generated from a pressure pulse in the photosphere and it ejects the chromosphere-corona transition region along the loop, expanding the underlying chromosphere into the corona. This expanding chromospheric material in a loop is regarded as a fibril. The shock propagates in the corona and collides with another transition region where a reflected shock and a penetrating shock are generated. The effect of the reflected shock on the motion of the fibril is weak. The fibril shows a nearly ballistic motion as observations suggest, if it does not extend beyond the summit of the loop. The corona in the loop is compressed nearly adiabatically by the fibril, and the enhanced coronal pressure leads the fibril finally to a retracting motion even if the fibril goes beyond the summit of the loop.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 261.     

Characterization of the amorphous state in metamict silicates and niobates by EXAFS and XANES analyses

X-ray absorption spectroscopy using synchrotron radiation has been applied to the investigation of the coordination geometries around Y, Zr and Nb atoms in metamict zircon, gadolinite, fergusonite, euxenite and samarskite. EXAFS and XANES spectra of their crystalline counterparts and synthetic compounds including ZrO₂, Y₂O₃, YNbTiO₆, YNbO₄, LiNbO₃, and NiNb₂O₆ were also measured for comparison. Metamict zircon shows a significant decrease in its Zr-O bond distances accompanying an increase in distortion of the Zr-O coordination polyhedra as compared with crystalline zircon. On the contrary, the average Nb-O bond distances and the symmetry of the coordination polyhedra around the Nb atoms in metamict euxenite and samarskite resemble those in the crystalline euxenite. Compared with crystalline fergusonite, a decrease in the distortion of the Nb-O octahedra is observed in metamict fergusonite. The structures of the second nearest neighbors (the metal-metal interactions) are largely disrupted in the metamict specimens except for metamict zircon and samarskite with high trivalent iron concentration. Nb in metamict samarskite is in octahedral coordination by oxygen and is similar to that in euxenite.     

Hydraulic and numerical study on the generation of a subaqueous landslide-induced tsunami along the coast

By carrying out the hydraulic experiments in a one-dimensional open channel and two-dimensional basin, we clarified the process of how a landslide on a uniform slope causes the generation of a tsunami. The effect of the interactive force that occurs between the debris flow layer and the tsunami is significant in the generation of a tsunami. The continuous flow of the debris into the water makes the wave period of the tsunami short. The present experiments apply numerical simulation using the two-layer model with shear stress models on the bottom and interface, and the results are compared. The simulated debris flow shows good agreement with the measured results and ensures the rushing process into the water. We propose that the model use a Manning coefficient of 0.01 for the smooth slope and 0.015 for the rough slope, and a horizontal viscosity of 0.01 m²/s for the landslide; an interactive force of 0.2 for each layer is recommended. The dispersion effect should be included in the numerical model for the propagation from the shore.     

Comparative geochemical,magnetic susceptibility,and fluid inclusion studies on the Paleoproterozoic Malanjkhand and Dongargarh granitoids,Central India and implications to metallogeny

The Malanjkhand granodiorite (MG) hosting economic copper mineralization and the hitherto barren Dongargarh granitoids (DG) have subtle differences in their petrographic and bulk geochemical features. The two plutons are contiguous and occur in the northern part of the Bhandara Craton in Central India with intervening volcanosedimentary sequence of the Dongargarh Supergroup amidst older gneisses. The Dongargarh granitoids studied in two smaller units have higher bulk magnetic susceptibility than the Cu-bearing MG; the majority of samples studied from the latter being ilmenite-series rocks. DG crystallized at higher pressures compared to MG. Plagioclase composition ranges from albite to high bytownite in MG, whereas its compositional range is restricted to high andesine in DG. However, both intrusions give identical temperature ranges estimated by binary feldspar thermometry. Biotite in MG shows higher Fe/Mg ratios, as well as a greater range of compositional variation, than that in DG. MG has a moderately fractionated rare earth element distribution pattern without any significant Eu anomaly, showing depletion in mid-range rare earth elements (REE) and no depletion in heavy REE. DG is characterized by a prominent negative Eu anomaly. Geochemical features indicate subtle differences in the nature of source rocks and/or melting processes responsible for the generation of the two granitoids. MG displays more consistent bulk chemical features and is possibly a result of crystallization from a homogeneous granodioritic melt. DG displays a greater diversity and possibly incorporated a significant felsic crustal component that contributed to the parent melt. A fluid inclusion study of quartz grains from the granitoids and barren quartz veins occurring in MG indicates identical low-temperature nature of the fluid in both cases. They differ from the fluid in the mineralized zone in MG in the absence of a high-temperature component and CO₂ in the fluid. Late-stage fluids in DG and associated barren quartz veins compare well with those from MG. The hydrothermal activity following the granite emplacement seems to have operated under identical temperature conditions, and the aqueous fluid at the two occurrences seems to have been broadly similar. In both cases, internal evolution of the exsolved fluid to low temperatures and moderate salinity are visualized. Based on the existing information, the lack of ore potential in DG may be attributed to the metal and volatile (water + halogens) deficient nature of the parental granitic melt.