Geochemistry, mineralogy and petrology of a new find of ultramafic lamprophyres from Bulljah Pool, Nabberu Basin, Yilgarn Craton, Western Australia

Four variously pipe or sill-like, Carboniferous ( ≈ 305 Ma) bodies have been located near the NE edge of the Archaean Yilgarn craton. The rocks comprise Ba---Ti-bearing tetraferriphlogopite-tetraferriannite, low Al---Ti-diopside, calcite, perovskite and groundmass titanomagnetite-chromite (up to 41.3% Cr₂O₃), with minor apatite, Mg---Mn ilmenite, rare-earth phosphate, K---Ba-feldspar (up to 17% BaO), baryte and an unidentified Ba---Zr silicate. The last three reflect very high whole-rock Ba (up to 5,652 ppm). Aegirine-rich pyroxenes occur in fenitic alteration assemblages. Together with high Si/Al and low Mg/Ca whole-rock geochemistry, these features are diagnostic of ultramafic lamprophyres (damkjernites and aillikites), although the rocks also show some affinities with classical kimberlites. Mineral concentrates from loam samples yield an array of minerals of mantle origin, including garnets (Dawson and Stephens' groups G1, 3, 5, 9 and 10), chromian diopsides (up to 6.2% Cr₂O₃), magnesiochromites (up to 20% MgO, 70% Cr₂O₃) and four compositional groups of ilmenites (low-Mn picroilmenites, Mn-rich, Mg-poor and two moderate Mn---Mg compositions). Actual spinel-lherzolite nodules are common in one body and the presence of spinel-and/or garnet-lherzolites can be inferred in the others from the concentrates. The Bulljah bodies are therefore of deep mantle origin, as confirmed by the recovery of a single microdiamond. They thus extend the field of potentially (if not necessarily economically) diamondiferous rocks beyond kimberlites and lamproites. When added to other recent lamprophyre finds, the Bulljah discoveries suggest that the Yilgarn craton could, like many other ancient cratons, be ringed and/or dotted by a diverse array of alkaline and lamprophyric rocks of varying ages which remain to be discovered.     

Arctic sea ice characteristics and associated atmosphere — Ice interactions in summer inferred from SMMR data and drifting buoys: 1979–1984

SMMR-derived sea ice concentrations for November 1978 – October 1984 in the Canada Basin are examined to determine temporal and spatial scales of variability in ice concentration and extent. Large regions of reduced-concentration ice are observed in late summer in four of the six years studied. Examination of the brightness temperature patterns and comparison of the SMMR-derived concentrations with visible-band imagery and drifting buoy temperatures support the interpretation of these features as true reductions in ice concentration. The observed areas of reduced concentration appears as a mixture of big floes andrazvodye, or open water areas of irregular shape and indefinite duration. Comparison with buoy-measured surface pressure and winds suggests that reduced ice concentrations are associated with regions of strong winds and divergence beneath low pressure systems.     

Observations of the performance of buildings during the 1985 Mexico earthquake,and structural design implications

Summary The high amplification of the 1985 Mexico City earthquake is explained by the large number of strong and nearly continuous cycles of 2 s period motion lasting for more than 30 s. The type of damage caused by the earthquake—particularly to engineered multi-storey buildings of high flexibility is described, and methods of adding damping and stiffness elements to reduce and resist earthquake demand forces are discussed.     

Surfactant-Induced Reductions in Soil Hydraulic Conductivity

Surfactant solutions are being proposed for in situ flushing of organic contaminants from soils and aquifers. The feasibility of surfactant additives in remediation may depend in large part on how these chemicals affect the hydraulic conductivity of the porous media. While there is evidence in the literature of conductivity loss during surfactant flushing (Miller et al. 1975; Nash et al. 1987), there has been little research on quantifying the process for unconsolidated sediments. Surfactant-affected hydraulic conductivity reductions were measured in two soils (Teller loam and Daugherty sand). Testing was done with eight surfactants at a variety of concentrations (10^-5 to 10^-l mole/kg), surfactant mixtures, and added solution electrolytes. The Teller was also tested with its organic matter removed. Maximum hydraulic conductivity decreases were 47 percent for the sand and more than two orders of magnitude for the loam. Surfactant concentrations, surfactant mixtures, soil organic content, and added solution electrolytes all affected the degree of conductivity reduction. Results indicate that surfactant-affected hydraulic conductivity losses should be considered prior to in situ remediation and may preclude surfactant use in some fine grain soils.     

Lessons from Ontake-san: A comparative analysis of debris avalanche dynamics

Dynamic aspects of the long runout Ontake-san debris avalanche are evaluated by a comparison of several models. An unsteady numerical model assumes two-dimensional flow of an incompressible biviscous or Newtonian fluid, represented as a continuum with a free surface. Internal deformation of the flowing mass is considered, as well as boundary resistances. Thus flow thinning and deposit shape as well as flow kinematics may be modeled. Parameters are adjusted to match observed runout, with additional constraints on velocity and emplacement time. With abundant constraints for Ontake-san, from careful field investigations by Japanese research teams, our analysis indicates that a substantial decrease in flow resistance occurred as a function of displacement. Constant-property models that match runout tend to overestimate the peak velocities and to underestimate the emplacement times. A staged increase in mobility in both constant volume and variable volume models leads to results consistent with field data. Runout in a channel overflow area was also modeled. Qualitatively similar results have been obtained by other researchers using simple sliding block models with empirical parameters, a slide block model with rational parameter selection, a modified flood simulation, and a multi-element frictional slide model. The relative merits of these models are compared.

The field mechanisms associated with this mobility increase with displacement are poorly understood, but the question is now identified as a target for future research at debris avalanche sites, and some plausible mechanisms are considered. The main reason probably involves the entrainment of river water and saturated sediment, leading to enhanced efficiency of fluid pressure mechanisms with undrained shear; in addition, progressive shearing reduced the mean particle size and angularity, and the cohesion and friction (and apparent viscosity) of avalanche debris near the wetted perimeter. Hydroplaning — the shearing of water films and slurries — may have occurred locally.     

A Synoptic Evaluation of Frequencies and Intensities of Extreme Three-and 24-Hour Rainfall in Louisiana*

This research classifies extreme three-hour and 24-hour rainfall events in Louisiana by synoptic weather types (Frontal, Gulf Tropical Disturbance, and Air Mass). These classes were used to analyze differences in frequencies and intensities of extreme rainfall. Significant differences were found in the storm frequencies by weather type. However, no significant differences were detected in rainfall intensities between weather types during either duration. These findings have a bearing on statistical procedures associated with estimating storm probabilities in the region.     

Application of GPS for transportation related engineering surveys

Summary The Texas State Department of Highways and Public Transportation(SDHPT) has been usingGPS for over two years to establish primary geodetic reference points for engineering projects and mapping control. In accordance with a Five YearGPS Implementation Plant developed in 1982, fourGPS, unmanned, automatic Regional Reference Point(RRP) stations will be installed by September 1, 1986. Five additional stations are planned as justified. EachRRP will consist of a dual frequencyGPS receiver that will ultimately track the satellites continuously. Operation of the receiver, telecommunications and other station keeping chores will be handled by a microcomputer. TheRRP station network will be controlled through another centrally located microcomputer which is also interfaced with a larger mainframe system. EachRRP is designed to service an area bounded by a200 KM radius and will act as the “other” receiver for roving field units operating in aGPS differential measurement mode. In order to meet the installation schedule, early decisions are being made concerning satellite tracking rates, operational scenarios, and telecommunications to facilitate development of the basic hardware and software systems. A period of continual enhancement to hardware, software andRRP operational procedures is expected asGPS technology expands.