Crystal chemistry of wadsleyite II and water in the Earth’s interior

Wadsleyite II is a variably hydrous magnesium-iron silicate phase similar to spinelloid IV and a potential host for H in the Transition Zone of the Earths mantle. Two separate samples of wadsleyite II synthesized at 17.5 GPa and 1400°C and at 18 GPa and 1350°C have been characterized by electron microprobe, single-crystal X-ray diffraction, visible, IR, Raman, and Mössbauer spectroscopies, and transmission electron microscopy including electron energy-loss spectroscopy. The two samples have the following chemical formulae: Mg_1.71Fe_0.18Al_0.01H_0.33Si_0.96O₄ and Mg_1.60Fe_0.22Al_0.01 H_0.44Si_0.97O₄. Mössbauer spectroscopy and electron energy loss spectroscopy (EELS) indicate that about half of the iron present is ferric. Refinement of the structures shows them to be essentially the same as spinelloid IV. Calculated X-ray powder diffraction patterns show only subtle differences between wadsleyite and wadsleyite II. The hydration mechanism appears to be protonation of the non-silicate oxygen (O2) and possibly the oxygens surrounding the partially vacant tetrahedral site Si2, charge-balanced by cation vacancies in Si2, M5 and M6. The unit cell volume of this phase and its synthesis conditions indicate that it may be an intermediate phase occurring between the fields of wadsleyite and ringwoodite, if sufficient trivalent cations are available. The unit cell parameters have been refined at pressures up to 10.6 GPa by single-crystal X-ray diffraction in the diamond anvil cell. The refined bulk modulus for the sample containing 2.8 wt% H₂O is 145.6 ± 2.8 GPa with a K of 6.1 ± 0.7. Similar to wadsleyite and ringwoodite, hydration has a large effect on the bulk modulus. The presence of this phase in the mantle could serve to obscure the seismic expression of the phase boundary between wadsleyite and ringwoodite near 525 km. The large apparent effect of hydration on bulk modulus is consistent with hydration having a larger effect on seismic velocities than temperature in the Transition Zone.     

Evidence of flandrian valley alluviation in staindale,North York Moors

The Dovedale Griff has incised into valley fill deposits in Staindale to expose sub-fossil wood at the base of a meander cut bank. The wood includes oak (Quercus sp.) driftwood, and apparently in situ stumps of willow (Salix sp.) and alder (Alnus sp.). An alder stump is dated at 6270 radiocarbon years BP. Fluvial gravels approximately 1±5 m thick have accumulated above the wood, which has been exposed by renewed incision.     

A correction model for conditional bias in selective mining operations

A nonlinear correction functionK(Z*) is proposed to transform any initial linear grade estimatorZ* into a conditional unbiased estimatorZ**=K(Z*) with reduced conditional estimation variance. Such a corrected estimator allows more accurate prediction of ore reserves at any level of selection performed during the mine lifetime. The correction is based upon an analytical or isofactorial representation of a bivariate distribution model of true gradeZ and its estimatorZ*. This correction model allows derivation of conditional estimation variances for both estimatorsZ* andZ** and provides a solution to the problem of change of support. A case study is presented and performance of the proposed correction model is evaluated in terms of actual conditional bias and mean squared errors. Results obtained stress the practical importance of the correction model in selective mining operations.     

Anisotropic compression of edingtonite and thomsonite to 6 GPa at room temperature

Polycrystalline samples of natural edingtonite (New Brunswick, Canada) and thomsonite (Oregon, USA) were studied up to 6 GPa using monochromatic synchrotron X-ray powder diffraction and a diamond-anvil cell with a methanol:ethanol:water mixture as a penetrating pressure-transmitting fluid. Unlike natrolite, previously studied under the same conditions, edingtonite and thomsonite do not show any apparent pressure-induced hydration (PIH) or phase transitions. All these fibrous zeolites are characterized by their anisotropic compressibilities, with the linear compressibilities of the fibrous chains (c-axis) being as small as one third of those perpendicular to the chains (a-, b-axes); for edingtonite, ₀ ^a =0.0050(3) GPa^–1, ₀ ^b =0.0054(2) GPa^–1, ₀ ^c =0.0034(1) GPa^–1; for thomsonite, ₀ ^a = 0.0080(2) GPa^–1, ₀ ^b =0.0084(2) GPa^–1, ₀ ^c =0.0032(1) GPa^–1. The pressure–volume data were fitted to a second-order Birch–Murnaghan equation of state using a fixed pressure derivative of 4. As a result of the 0000-type connectivity of the chains, the bulk modulus of edingtonite is found to be about 40% larger than that of thomsonite; K^EDI ₀=73(3) GPa, K^THO ₀=52(1) GPa. Distance least-squares refinements were used to model the expected framework, following the observed linear compression behaviors. The chain-bridging T–O–T angle is proposed to be correlated with the different compressibilities across the chains in each framework type.     

Heavy mineral characteristics of the Neogene–Quaternary sediments from the southern part of the Blagoevgrad Basin, SW Bulgaria

The Blagoevgrad Basin, a graben filled with Neogene–Quaternary continental sedimentary successions, is one of the most prospective placer-gold bearing regions in southwestern Bulgaria. The Quaternary sediments have been well explored and economically prospective areas have been identified. Previous studies indicated very limited occurrences of placer gold in the Neogene sediments, the genesis of which is connected with resedimentation of Paleogene sediments from the adjacent Bobov dol Basin to the north. From these previous studies, a detailed allo- and lithostratigraphic scheme, and paleogeographic models were developed.The present study aimed to evaluate the plausibility of the existing stratigraphic schemes and paleogeographic models for the area, through detailed study of the heavy mineral fraction of the Neogene and part of the Quaternary sediments from the southern part of the Blagoevgrad Basin. Additional objectives were to determine the mode of occurrence and the stratigraphic position of the placer gold in the Neogene sediments, and to investigate possible source areas. Special attention was paid to the mineral composition and the structure of the opaque detrital Fe–Ti oxide minerals, and the typologic features of the zircons. The results obtained could be used as a provenance indicator and for determination of the nature of the source area and the processes that operated therein.A very important finding is the discovery of placer gold in an additional three Neogene units. The morphologic features of the gold grains indicate short transport or proximity to the primary source. This interpretation is inconsistent with existing hypotheses on the origin and presence of the gold in the sediments of the basin. The characteristics of the magnetic heavy mineral fraction, and the morphologic features of zircon grains in auriferous samples, indicate the diorites and gabbro-diorites from the Strouma Diorite Group, which outcrop along the eastern edge of the graben, as a possible source.The stratigraphic distribution of the heavy minerals fully supports the plausibility of the existing detailed allo- and lithostratigraphic subdivision, and the paleogeographic model for the development of the southern part of the basin. Also, the results provide support for the soundness of an allostratigraphic approach for the study and exploration of placer deposits in basins similar to the Blagoevgrad.     

Summer rain events in south-east Asia: Spatial and temporal variations

During the summer monsoon period in south-east Asia marine airstreams normally prevail at the south China coast. However, when tropical cyclones approach then polluted airmasses from south-eastern China can impart high ionic concentrations and high acidity to rainwater. This is illustrated by two examples and the small-scale horizontal variations in rainwater composition are minor during these episodes. Since long-term quality-assured studies of the composition of rainwater in south-east Asia are scarce, the results at three sampling sites in Hong Kong during summer monsoon periods are compared with previous data from the same season. The results for the mid- to end-1990's show a similar trend to those for the ambient concentrations of sulphate and nitrate in aerosol in Hong Kong, which show flattened trends from 1995 to 1999. A marked increase in acidity is found in the summer monsoon period of 2004 which is attributed to the greater proportion of approaching cyclone weather systems in the dataset, reflecting both the increased local emission sources and the burgeoning economic growth of the Pearl River Delta Region. Comparison of the rainwater composition with that at other south-east Asian cities during the summer monsoon period shows that it is most acidic in Hong Kong.     

Space operation system for Chang’E program and its capability evaluation

Space operation for China’s first lunar exploration program, Chang’E will be provided by the S-band aerospace Telemetry, Tracking and Command (TT&C) network designed for China’s manned space program. This is undoubtedly a great challenge to the ground TT&C system. The largest antennas of China’s S-band aerospace TT&C network has an aperture of only 12 m. A series of technical measures have been taken into the designing of the spacecraft-ground TT&C system to ensure that such antennas can communicate with Chang’E-1 lunar probe 400,000 km away. These include installation of high-gain directional antennae and medium-gain omni-directional antennae for the probe, adding channel encoding to the downlink channel, using both high and low data rates for information transmission and upgrade and design of ground equipment terminals. Among them, the omni-directional antenna will operate in the earth-ground transfer orbit phase and the directional antenna will operate in the lunar orbit phase. These measures satisfy the spacecraft-ground link and program design requirements. To provide accurate navigation for the probe during its Earth-Moon flight and initial lunar orbiting flight, China’s VLBI system designed for astronomical observations, will also be used besides the ranging and range rate measurement capabilities of the S-band TT&C network. The purpose is to provide 100 m accuracy in position determination during lunar orbit. This paper describes the system design, technical challenges, solutions and capability evaluation of space operation for Chang’E-1.     

Seismic upgrade of hydraulic fill dam by buttressing

The vulnerability of hydraulic fill dams under strong earthquake shaking has long been recognized. When located in areas of high seismic hazard, seismic upgrading of these types of dams is often required to meet current dam safety standards. Selection of an appropriate design concept for seismic upgrading of such dams requires careful consideration of seismically induced deformations when the hydraulic fill is to remain as part of the dam. This paper presents a case history of the seismic upgrade of Butt Valley Dam, a hydraulic fill dam located in Northern California. The dam was strengthened to withstand the Maximum Credible Earthquake (MCE) by buttressing of its upstream and downstream slopes. The paper discusses the evaluation of alternatives to upgrade the dam, the design criteria, and the design and analysis of the seismic upgrade. It is shown that a conservative and robust design was developed based on well-established engineering principles and multiple lines of defense, and sound use of analysis procedures including finite-difference non-linear dynamic deformation analyses.     

The Gibbs energy formulation of the α, β, and γ forms of Mg2SiO4 using Grover, Getting and Kennedy's empirical relation between volume and bulk modulus

 The empirical linear relation between volume and logarithm of bulk modulus of a material, discovered by Grover, Getting and Kennedy is taken as the basis for our equation of state. Using the latest experimental information on the adiabatic bulk modulus, the equation of state is applied to the three polymorphs of Mg₂SiO₄ to develop a consistent dataset of their thermodynamic properties in the temperature range of 200–2273 K and a pressure range of 0.1 MPa–30 GPa. The results imply that the bulk sound velocity contrast (v ^β−v ^α)/v ^α increases with temperature along the α–β phase boundary and reaches the value 8.9% at 13.5 GPa, a pressure equivalent to 410 km depth in the Earth. The bulk sound velocity contrast (v ^γ−v ^β)/v ^β decreases with temperature along the β–γ phase boundary and becomes less than 0.7% at temperatures and pressures equivalent to those associated with the 520-km seismic discontinuity in the Earth. Received: 1 August 2000 / Accepted: 1 March 2001     

压实碎石填土工后检测方法的试验研究

压实碎石填土主要由碎石构成，不能取得原状土试样，难以准确测定压实系数。其工后检测方法宜以重型圆锥动力触探试验、旁压试验为主，进行综合检测和评价。