Rare earth geochemistry of fused ophiolitic and alpine lherzolites

Partial fusion hypotheses have been proposed for the origin of lherzolite-harzburgite alpine peridotite associations. Analyzed lherzolites from Othris, Ronda, Lanzo and Beni Bouchera, have light REE depleted to chondritic REE abundances, and clinopyroxenes contain most of the REE relative to depleted olivine and orthopyroxene. Variation in the level of REE enrichment within these lherzolites indicates mantle heterogeneity probably caused by partial melting processes. The Beni Bouchera spinel lherzolite and the Othris plagioclase lherzolite are the best candidates for relatively undepleted mantle based on REE studies. Fractional fusion calculations (15–25%) reveal that partial melts have REE characteristics somewhat similar to oceanic tholeiites. Conversely, computed source peridotites from oceanic tholeiites (Schilling, 1975) are similar to the alpine lherzolites reported here. Alpine lherzolites are, however, depleted in trace elements (K, Rb, Sr and Ba, Menzies and Murthy 1976). Since the lherzolites have an undepleted major, minor and REE chemistry close to that of pyrolite, the lost trace element-rich fraction must represent a small degree of melting. It is proposed that alpine lherzolites are residue left after the loss of a nephelinitic/alkalic fraction, ([Ce/Yb]_N=2.0–4.01) representing a small degree of partial fusion. This labile fraction may have existed as an intergranular phase or hydrous mineral prior to melting.     

Free and steady state vibration of non-linear structures using a finite element–non-linear eigenvalue technique

The problem of free vibration of non-linear structures is considered initially. It is shown that this problem can be represented as a non-linear eigenvalue problem. Variational principles for non-linear eigenvalue problems are defined. These variational principles are implemented with finite element models to define numerical approximations for the free vibration problem. The solution of these approximate equations provides a set of non-linear modal vectors and natural frequencies which vary with the amplitude of the solution. The non-linear eigenvalue parameters can be used in modal expansion approximations for the non-linear transient or steady state response of structural systems. To demonstrate the proposed techniques the free vibration and steady state vibration characteristics of a geometrically non-linear circular plate are determined.     

On the efficiency with which aerosol particles of radius larger than 0.1 μm are collected by simple ice crystal plates

A theoretical model is presented which allows computing the efficiency with which aerosol particles of radius 0.1r10 m are collected by simple ice crystal plates of radius 50a _c 640 m in air of various relative humidities, temperatures and pressures. Particle capture due to thermophoresis, diffusiophoresis and inertial impaction are considered. It is shown that the capture efficiency of an ice crystal in considerably affected by phoretic effects in the range 0.1r1 m. For aerosol particles ofr>1 m the efficiency is strongly controlled by the flow field around the crystal and the density of the aerosol material. Trajectory analysis also predicts that aerosol particles are preferentially captured by the ice crystal rim. Our theoretica results are found to agree satisfactorily with the laboratory studies presently available. Comparison shows that for the same pressure, temperature and relative humidity of the ambient air ice crystal plates are better aerosol particle scavengers than water drops.     

On the error introduced into Stokes' formula by applying the Honkasalo tidal gravity term

The error caused by using the Honkasalo tidal gravity term in geoid computations with Stokes' formula is discussed. It is pointed out that the relatively large value of the error to a great extent is generated by interaction between the Honkasalo term and the weight function in Stokes' formula.     

Fault-bounded blocks and their role in localising sedimentation and deformation adjacent to the alpine fault, southern New Zealand

Continental transform boundaries in detail consist of zones of fault-bounded blocks adjacent to the principal active transform fault(s). Relative movement of these blocks in response to plate boundary motions gives rise to differential vertical displacements of the earth's crust and hence exercises a degree of control on the tectonic evolution of sedimentary basins adjacent to the transform boundary. The Cenozoic sedimentary basins of southwest New Zealand have several features in common that may be attributed directly to the movement on the adjacent plate boundary. However, their location, detailed sedimentary evolution and tectonic development may best be understood in the context of the relative displacements of a number of fault-bounded blocks, in response to the plate motions. In particular, movements of the Fiordland block, bounded by the Alpine and Moonlight fault zones, exercised a large measure of influence on the development of the basins. The tectonic model presented is consistent with plate boundary motions inferred from marine magnetic anomalies while at the same time providing an explanation for many of the more detailed features of the basins.     

A scheme for computing surface fluxes from mean flow observations

A computational scheme is developed for estimating turbulent surface stress, sensible heat flux and humidity flux from mean velocity, temperature and humidity at a single height in the atmospheric surface layer; conditions at this reference level are presumed known from observations or from a numerical atmospheric circulation model. The method is based on coupling a Monin-Obukhov similarity profile to a force-restore formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux and surface temperature. A self-contained formulation is presented including parameterizations for solar and infrared radiant flux at the surface.In addition to reference-level mean flow properties, the parameters needed to implement the scheme are thermal heat capacity of the soil, surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity and atmospheric transmissivity.Sample calculations are presented for (a), constant atmospheric forcing at the reference level, and (b) variable atmospheric forcing corresponding to Kahle's (1977) measurements of windspeed, air temperature and radiometer soil surface temperature under dry vegetatively sparse conditions in the Mohave Desert in California. The latter case simulated the observed diurnal variations resonably well for the parameters used.Consultant, Atmospheric Sciences Division, Department of Energy and Environment, Brookhaven National Laboratory, Upton, N.Y., pc11973, U.S.A.     

Ground retreat and slope evolution on regraded surface-mine dumps,waunafon, gwent

Ground retreat was monitored on two vegetated and two unvegetated profiles over a five-year period. The average annual retreat of the two unvegetated profiles was 5.84 mm and 3.62 mm; that of the two vegetated profiles 2.34 mm and 2.07 mm. Slope evolution was controlled by the mid-slope-ward migration of two zones of accelerated erosion and the resulting replacement of a central rectilinear slope segment by the upper and lower slope elements.     

An investigation of rare-earth mobility: Fenitized quartzites,Borralan complex,N.W. Scotland

Examples of fenitization of pure quartzites provide valuable insight into the relative mobility of elements. This investigation of fenites from the Borralan complex shows that rare-earth elements are mobile and added during fenitization of quartzite. The resulting normalized patterns are distinctive in their enrichment of the light rare earths and steep drops in the interval Nd-Eu. In terms of rare-earth geochemistry, no difference can be found between the sodic and the potassic trends of fenitization at Borralan. Concentrations of mobile elements define straight-line plots through the origin, heretofore considered a criterion indicative of a fractional crystallization process.Present address: Department of Geological Sciences, McGill University, 3450 University Street, Montreal, Que. H3A 2A7, Canada