Re-os isotope systematics of the Taklimakan Desert sands, moraines and river sediments around the taklimakan desert, and of Tibetan soils

Reported here are the first ¹⁸⁷Os/¹⁸⁸Os ratios and abundances of Os and Re for Taklimakan Desert sands and glacial moraines from the Kunlun Mountains. Osmium isotopic data are also reported for river sediments around the Taklimakan Desert, river sediments from the Kunlun and Tianshan Mountains, Tibetan soils and loesses from the Loess Plateau, as well as Sr and Nd isotopic data for these samples. The Taklimakan Desert sands from various regions show surprisingly homogeneous Os isotopic ratios (¹⁸⁷Os/¹⁸⁸Os = 1.29 ± 0.08) and abundances (Os = 11 ppt), with some variations in Re abundances (Re = 130 to 260 ppt) and ¹⁸⁷Re/¹⁸⁸Os ratios (60 to 140). The ¹⁸⁷Os/¹⁸⁸Os ratios for the Taklimakan Desert sands are close to the average for Kunlun moraines, river sediments around the Taklimakan Desert sands, and the Tibetan soils, supporting the idea that the Taklimakan Desert sands are derived from moraines and river sediments around the desert or from Tibetan soils and are homogenized by aeolian activity in the desert. Furthermore, the Os isotopic data for the sediments studied here are compared with those (¹⁸⁷Os/¹⁸⁸Os = 1.04, Os = 32 ppt, Re = 206 ppt, ¹⁸⁷Re/¹⁸⁸Os = 35) of loesses from the Loess Plateau reported elsewhere, and it is concluded that the Re-Os data for the loess can be used as proxy for the upper continental crust.     

A search for absorption of Mg and Ca compounds in molecular clouds towards Galactic continuum sources

Absorption lines of MgH and CaH N  = 1 − 0 transitions were searched for in foreground molecular clouds towards the continuum sources associated with Sgr B2 (M) and W49A (N). None of these lines was detected with our sensitivity level of ∼20 mK. Millimetric absorption lines of MgO, MgOH, CaO and CaOH were also searched for towards Sgr B2 (M) without success. The fractional abundances relative to molecular hydrogen are ≲ 1.0 × 10⁻¹¹ for MgH, ≲ 7.9 × 10⁻¹³ for MgO, ≲ 1.6 × 10⁻¹⁰ for MgOH, ≲ 1.6 × 10⁻⁹ for CaH, ≲ 2.0 × 10⁻¹² for CaO, and ≲ 2.5 × 10⁻¹⁰ for CaOH, respectively. The low abundances measured in absorption indicate that a significant fraction of interstellar magnesium and calcium cannot be tied up in their monohydrides, monoxides and monohydroxides. The low abundance of MgH also implies that grain-surface chemistry involving magnesium is not efficient and that magnesium is depleted on to grains to a factor of ≳ 10^2.5 in well-shielded molecular clouds.     

Natural regions of Japan

In order to subdivide the natural regions of Japan, first, the regional subdivisions or distributions of geology, landforms, soils, climates, hydrology, flora, forests and vegetations are shown separately. The characteristics of the subdivided regions or zones are described briefly to illustrate the distribution of every element in Japan. Secondly, a tentative division of natural regions of Japan is given in reference to the subdivisions or distributions mentioned in the first part. The numbers of the natural regions of Japan tentatively proposed in this paper are 7 in the 1. order, 20 in the 2. order and 58 in the 3. order. The average area of the 3. order regions in Kyûshû, Shikoku, Honshû and Hokkaidô is about 8,100 km², which implies a meso-scale dimension. The names of the regions in the 2. order are: I₁) Nansei Islands, I₂) Daitôjima, II₁) Ogasawara Islands and others, II₂) Minamitorishima (Marcus Is.), III₁) Pacific coast (Nankai), III₂) Mountain area of SW Japan, III₃) NW Kyûshû, III₄) Inland Sea region, III₅) Pacific side of Central Japan, IV₁) Izu Islands, IV₂) Kanto-tosan, IV₃) Pacific side of NE of Honshu, V₁) San'in district, V₂) NW of Central Japan, VI₁) NE of Central Japan and S of N Honshû, VI₂) Japan Sea side of N Honshû, VI₃) SW Hokkaidô, VII₁) Pacific side of Hokkaidô, VII₂) E of Hokkaidô, and VII₃) W of Hokkaidô.

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Short note: Crustal deformation in the key stone network detected by satellite laser ranging

The paper presents the results of crustal deformation, as evidenced by changed station coordinates, in the Tokyo metropolitan area detected by the satellite laser ranging (SLR) technique. The coordinates of two Key Stone SLR stations, Tateyama and Kashima, were determined from 4 weeks of orbital arcs of the LAGEOS-1 and LAGEOS-2 satellites with respect to 16 SLR stations kept fixed in the ITRF2000 reference frame. The station coordinates were calculated using the NASA GEODYN-II orbital program. The orbital RMS-of-fit for both satellites was 16 mm. The standard deviation of the estimated positions was 3 mm. A jump of about 5 cm in the baseline length between the Kashima and Tateyama stations was detected in June–August 2000 by VLBI and GPS techniques. This work confirms this crustal deformation as determined by SLR and vice versa. Analysis of coordinates of these stations shows that this effect was caused by a 4.5-cm displacement of the Tateyama station in the north-east direction. The change in the vertical component was not significant.     

Phase relations and equation-of-state of aluminous Mg-silicate perovskite and implications for Earth's lower mantle

We have investigated the effect of Al³⁺ on the room-temperature compressibility of perovskite for stoichiometric compositions along the MgSiO₃-AlO_1.5 join with up to 25 mol% AlO_1.5. Aluminous Mg-perovskite was synthesized from glass starting materials, and was observed to remain a stable phase in the range of ∼30-100 GPa at temperatures of ∼2000 to 2600 K. Lattice parameters for orthorhombic (Pbnm) perovskite were determined using in situ X-ray diffraction at SPring8, Japan. Addition of Al³⁺ into the perovskite structure increases orthorhombic distortion and unit cell volume at ambient conditions (V₀). Compression causes anisotropic decreases in axial length, with the a axis more compressive than the b and c axes by about 25% and 3%, respectively. The magnitude of orthorhombic distortion increases with pressure, but aluminous perovskite remains stable to pressures of at least 100 GPa. Our results show that substitution of Al³⁺ causes a mild increase in compressibility, with the bulk modulus (K₀) decreasing at a rate of −67±35 GPa/X_Al. This decrease in K₀ is consistent with recent theoretical calculations if essentially all Al³⁺ substitutes equally into the six- and eight-fold sites by charge-coupled substitution with Mg²⁺ and Si⁴⁺. In contrast, the large increase in compressibility reported in some studies with addition of even minor amounts of Al is consistent with substitution of Al³⁺ into six-fold sites via an oxygen-vacancy forming substitution reaction. Schematic phase relations within the ternary MgSiO₃-AlO_1.5-SiO₂ indicate that a stability field of ternary defect Mg-perovskite should be stable at uppermost lower mantle conditions. Extension of phase relations into the quaternary MgSiO₃-AlO_1.5-FeO_1.5-SiO₂ based on recent experimental results indicates the existence of a complex polyhedral volume of Mg-perovskite solid solutions comprised of a mixture of charge-coupled and oxygen-vacancy Al³⁺ and Fe³⁺ substitutions. Primitive mantle with about 5 mol% AlO_1.5 and an Fe³⁺/(Fe³⁺+Fe²⁺) ratio of ∼0.5 is expected to be comprised of ferropericlase coexisiting with Mg-perovskite that has a considerable component of Al³⁺ and Fe³⁺ defect substitutions at conditions of the uppermost lower mantle. Increased pressure may favor charge-coupled substitution reactions over vacancy forming reactions, such that a region could exist in the lower mantle with a gradient in substitution mechanisms. In this case, we expect the physical and transport properties of Mg-perovskite to change with depth, with a softer, probably more hydrated, defect dominated Mg-perovskite at the top of the lower mantle, grading into a stiffer, dehydrated, charge-coupled substitution dominated Mg-perovskite at greater depth.     

Occurrence of Free-Gas Associated with Methane-Hydrate-Bearing Formations in the MITI Nankai Trough Wells, Offshore Tokai, Japan

Abstract. The MITI Nankai Trough wells were drilled for exploration of methane-hydrate-bearing sediments in association with seismic inferred bottom simulating reflectors (BSRs). In this project, log data showed low velocity compressional-wave (P-wave) layers below methane-hydrate-bearing formations. Dipole shear sonic acoustic tools (DSI) could not acquire accurate compres-sional velocity in this zone, thus it was not possible to accurately correlate between logging, VSP and surface seismic profiles.
Small amount of gas was presumed to cause the problem in obtaining the low velocity P-wave data. VSP interval velocity data was used to assess the DSI inferred low-velocity layer, which showed lower values than the velocity of the drilling muds. Synthetic seismogram was created by VSP-compensated velocity to compare against corridor stack of VSP. As a result, the depths above and below the methane-hydrate-bearing interval were correlated with synthetic seismograms and reflectivity events on the VSP profiles. By using this correlation technique, distribution of methane-hydrate-bearing formations and free-gas-bearing formations can be determined.     

Palaeoenvironmental change in Java island and its surrounding areas

Palaeoenvironment in Java island and its surrounding areas since the last interglacial stage was reconstructed initially using previous studies by various researchers. The karst area in Gunung Sewu on Java island was also examined by the authors in order to reconstruct the palaeoenvironment through the process of karstification. Summarizing the evidence related to palaeoclimate in the various areas made it clear that the palaeoclimatic condition was cooler and drier at the Last Glacial Maximum 18 000 yr BP, than today. Formation of dry valleys in Gunung Sewu was conditioned by lowering of sea-level, and establishment of a cool and extremely dry climate. Subsequent to the initial reconstruction, the results of the estimated palaeoclimate at 18 000 yr BP were plotted at the respective points where the samples were obtained, and maps for northern winter and northern summer were constructed showing the estimated streamlines of monsoon circulations, polar frontal zones and intertropical convergence zones, in order to better explain the distribution of the palaeoclimate conditions of the area. ©1997 John Wiley & Sons, Ltd.     

Effect of faceting on pore geometry in texturally equilibrated rocks: implications for low permeability at low porosity

The pore geometry of texturally equilibrated rocks is controlled by the interfacial energy ratio between grain boundaries and solid–liquid boundaries. Faceting at pore walls, which is a common feature of pore networks in rocks, strongly affects the liquid distribution. We investigated the effects of faceting on the equilibrium pore geometries based on image analysis of several systems with various degrees of faceting and dihedral angles. The degree of faceting was assessed by the F value, which is the ratio of the flat interface length at the pore wall to the length of total interfacial boundary between solid and liquid. The F values tend to increase with increasing liquid volume fraction. Little-faceted systems show relatively homogeneous liquid distribution. Moderately-faceted systems with a higher dihedral angle (∼55°) are characterized by development of large pores surrounded by faceted walls and complementary shrinkage of triple junction tubes, whereas strongly faceted systems with a low dihedral angle show no evidence of shrinking triple junction tubes, although most pores are surrounded by faceted pore walls. The faceted systems tend to produce more facet boundaries at the pore walls due to the difference of interfacial energies between the flat and curved surfaces. In the systems with the same degree of faceting, heterogeneity of liquid distribution tends to decrease with dihedral angle. For faceting systems, the permeability of texturally equilibrated rocks with low liquid fraction would be significantly decreased by the relative reduction of triple junction volumes or by closure of channels along grain edge due to the truncation of facet walls.