Crystal chemistry of merrillite from Martian meteorites: Mineralogical recorders of magmatic processes and planetary differentiation

Merrillite is a ubiquitous accessory phase in a variety of Martian meteorite lithologies. The Martian merrillites exhibit a positive correlation between Mg# and Na and a negative correlation between Mg# and both Mn and vacancies in the octahedral Na‐site. Their REE patterns are varied and range from LREE‐depleted to LREE‐enriched. The dominant cation substitutions in the Martian merrillites are Fe²⁺_{VI Mg‐site}?Mg²⁺_{VI Mg‐site} and Ca²⁺_{VI Na‐site} +  □_{VI Na‐site}?2Na⁺_{VI Na‐site}. The REE substitution into the 8‐fold coordinated Ca‐site is accommodated by the coupled substitution Ca_{VIII Ca‐site} + (Na)_{VI Na‐site} ?(Y³⁺ + REE³⁺)_{VIII Ca‐site} + □_{VI Na‐site}. The REE substitution is significantly more prevalent in lunar merrillite and can be used as a “fingerprint” to distinguish lunar from Martian meteorites. The substitution of OH^? (whitlockite) and/or F^? (bobdownsite) for O^2? on one of the phosphate tetrahedrons appears to be rather insignificant. The correlations among Na, Mg#, Mn, and Na‐site vacancies are linked to the premerrillite crystallization history of the melt and the crystal chemical behavior of the Mg‐ and Na‐sites. The former reflects the sequence and extent of plagioclase and pyroxene crystallization. The differences in REE pattern shapes among the merrillites reflect source regions for the Martian basalts and the shapes are not greatly perturbed by the crystallization history. The occurrence of merrillite does not imply low‐volatile component in the Martian magmas. However, the low whitlockite and bobdownsite contents suggest that these samples were not altered by hydrothermal fluids and therefore not reset owing to aqueous fluid interactions. Consequently, the young ages of the shergottites are probably true igneous crystallization ages.     

Non-linear amplification of a magnetic field driven by cosmic ray streaming

One-, two- and three-dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large-amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently transferred to the perturbed magnetic field of the Alfvén waves, and the non-linear time-scale of the growth of the waves is found to be very rapid, of the order of the gyro-period of the cosmic ray. Thus, a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the cosmic ray acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy Galactic cosmic ray problem, where the cosmic rays themselves provide the fields necessary for their acceleration.     

An engineering geological appraisal of the sandstones of the Clarens Formation,Lesotho, in relation to tunnelling

Summary The Delivery Tunnel South forms part of a system of tunnels for conveying water from Lesotho to South Africa. The tunnel was excavated primarily by tunnel boring machine in the sandstones of the Clarens Formation. These sandstones are uniformly graded and fine grained with quartz being the most abundant mineral. They are mostly of aeolian origin. Their unconfined compressive strength varies appreciably, from moderately strong to extremely strong. The boreability of the sandstones was investigated by the Norwegian Institute of Technology tests and the total hardness. These tests showed that these sandstones would be relatively easy to bore, although moderately abrasive. The prediction proved correct. In fact, excavation of the tunnel was completed 20 months ahead of schedule, the rock conditions being better than expected. The long-term durability of these sandstones was investigated to establish criteria for concrete lining of the tunnel. A series of tests were undertaken to evaluate the durability. These included a number of soaking tests using different fluid media, wet and dry testing, erosion tests and brushing tests. This testing programme suggested that concrete lining of the intact sandstone was probably only required where the strength of the sandstone was less than 20 MPa and that therefore only a small percentage of the tunnel need be lined.     

Rehabilitation of industrial areas: case histories from England and Germany

 Contaminated and possibly hazardous ground represents a problem in all of the industrialized countries of the world. The investigation of a site that is suspected of being contaminated differs somewhat from a routine site investigation. Sampling of soils, groundwater and gas-producing material may be required. Various precautions may be necessary in doing this and operatives may have to wear protective clothing. Four case histories have been chosen to illustrate different aspects of the rehabilitation of abandoned contaminated land, namely, investigation, assessment, ground treatment and redevelopment. The first comes from Leeds in West Yorkshire, England, and outlines how a site investigation was undertaken and the nature of the contamination present, together with a note on the suggested redevelopment. The remaining three case histories are taken from the heavily industrialized district of the Ruhr in Germany, where extensive mining of coal and associated industries were developed from the mid-19th century onwards. The first considers the site of the former Graf Moltke mine near Essen. In this instance, the somewhat novel methods of data assessment and ground treatment are dealt with. The Mont Cenis site at Herne-Sodingen is one of the more notable old mining/industrial sites undergoing redevelopment in the state of North Rhine Westphalia. Hence, the case history concentrates of this aspect of rehabilitation. This involves not only the construction of new and interesting structures but an attempt to reduce energy consumption in an attempt to effect the concept of sustainable development of an urban area. The last example deals with the abandoned site of the Minister Achenbach mine at Lünen, where the ground conditions were further complicated by the presence of old bomb craters that had been filled with a variety of materials. In addition, because of the suspected presence of former foundation structures in the ground an electromagnetic survey was carried out across part of the site, the areas of high conductivity suggesting their presence. Received: 15 September 1999 · Accepted: 14 March 2000     

Extending the known distribution of the Younger Dryas Vedde Ash into northwestern Russia

The known distribution of wind‐blown Vedde Ash (ca. 10.3 ka BP) has been extended to the Karelian Isthmus in northwestern Russia. This has been possible as the result of a density separation technique that separates the rhyolitic Vedde Ash shards from the minerogenic host sediment. The Vedde Ash occurs in the middle of a pollen zone with high percentages of, for example, Artemisia and Chenopodiaceae, suggesting that the Younger Dryas (or GS‐I in the GRIP ice‐core event stratigraphy) was cold and dry throughout its duration. This is in agreement with sites in south Sweden where the Vedde Ash also occurs in the middle of a pollen zone dominated by Artemisia, Chenopodiaceae and Cyperaceae. Copyright © 2000 John Wiley & Sons, Ltd.     

Skolithos pipes as strain markers in mylonites

It is argued that mylonite zones result from translatory movements between rock masses and that the deformation mechanism is one of simple shear. Evidence is adduced to show that the mylonite zones in the Moine Thrust Belt of northwestern Scotland were developed in association with the inverted limbs of early Caledonian folds which trend parallel to the thrust front. On this basis a method is developed for the determination of shear strain from parameters which can be measured in mylonites which contain deformed Skolithos worm burrows. Very large strains are indicated (γ - 10). Some general implications are discussed.     

Strengthening ties in production systems. Two approaches exemplified by the Volvo case

The effects of corporate efforts to reduce tied-up capital is exemplified by the production system of Volve cars. Two approaches are applied. The first one shows how Volvo gradually integrated production units into the system, through takeovers and new establishments. The second one discusses the integration of one particular process, the body assembly, against varying technologies and contracts of cooperation between the two companies involved.