The petrogenesis of an I-type volcanic-plutonic suite: The St. Marys Porphyrite,Tasmania

The Devonian I-type St. Marys Porphyrite (388±1Ma) comprises two petrographically similar units, an 800 m thick pyroclastic sheet (compositionally dacite and rhyolite) and a subvolcanic feeder dyke. The pyroclastics are crystal-rich and contain (in order of decreasing abundance) plagioclase, quartz, biotite, augite, hypersthene and sanidine phenocrysts in an aphanitic groundmass.The early phenocryst assemblage clinopyroxene+orthopyroxene+plagioclase was followed by crystallisation of less magnesian pyroxene, more sodic plagioclase and biotite, quartz and K-feldspar. The phenocrysts crystallised at high temperature, between 1,000°-850° C, and at a pressure of 2.5±1 kb from a water undersaturated (<2.5 wt.%) magma in a chamber underlying the intrusive centre.At least two eruptive phases are present in the pyroclastic pile, each commencing with rhyolite. Bulk chemical variation probably reflects a zonation in the magma chamber prior to eruption. The low pressure phenocryst crystallisation conditions and the pyroxene Fe-enrichment trend with falling temperature support a fractional crystallisation model. The chemical variation can be explained by 20% fractional crystallisation involving plagioclase, quartz, biotite and pyroxene in proportions similar to modal phenocryst abundances.Volcanics like the St. Marys Porphyrite preserve evidence of their early magmatic history by quenching of mineral phases. Textural relationships and physico-chemical parameters deduced from the St. Marys Porphyrite are applicable to the interpretation of I-type granitoids in eastern Australia and elsewhere and constrain petrogenetic models for their genesis. Pyroxene cores of hornblende grains, pyroxene inclusions in plagioclase and corroded cores of plagioclase crystals may be formed through magmatic crystallisation and need not represent restite.     

Mineralogy of New Caledonian metamorphic rocks

The compositions of metamorphic pyroxenes from blueschists in northern New Caledonia are investigated. Aegerine-augite occurs in siliceous metasediments and aegerine in some low-grade sodic basic schists. Calcic metamorphic pyroxene (omphacite and chloromelanite) appears first in metabasalts in higher grades of the lawsonite zone and is widespread in metamorphosed igneous rocks and quartzofeldspathic gneisses of the epidote zone. Omphacites in basic rocks have higher Mg∶Fe ratios and are less jadeitic than omphacites from adjacent interbedded quartzofeldspathic gneisses. With increasing metamorphic grade pyroxenes become more jadeitic and diopsidic at the expense of their acmite component. Elemental partitioning between coexisting pyroxenes, garnets and amphiboles from in situ regional metamorphic rocks is generally regular, suggesting equilibrium crystallization. Omphacite appears to be a stable phase within blueschist facies over a temperature range of at least 350° to 550° C. The “eclogitic” assemblage almandine-omphacite is stable within the earth's crust in metamorphosed sediments and igneous rocks over a temperature range of 400° to at least 550° C. No estimate of absolute pressures involved in metamorphism in the Ouégoa district can yet be made.     

Observations on white island volcano,New Zealand

White Island is a complex of two overlapping cones constructed of lava flows, agglomerates and unconsolidated and unsorted ash and tuff beds. Remnants of a welded-tuff flow have been found on the north-east flank of the volcano. Since the extrusion of the youngest lava flow the young cone has been breached to the south-east and deeply eroded. White Island lavas are porphyritic augite-hypersthene-labradorite andesites. One young lava flow is unusually rich in Na₂O and contains groundmass sodian ferroaugite instead of the normal augite and hypersthene. The unusual groundmass features of this andesite are believed to be the result of contamination. Volcanic, plutonic and gneissic xenoliths have been found in the White Island lavas. Three new analyses of White Island andesites are given together with an electron microprobe analysis of a groundmass glass from one of the andesites. The White Island andesites are believed to have formed from the hybridisation of a primary mantle-derived andesitic magma with crustal material below the base of the Mesozoic New Zealand Geosyncline.     

On the origins of trapped helium,neon and argon isotopic variations in meteorites—II. Carbonaceous meteorites

Data are presented from stepwise heating experiments on five carbonaceous chondrites: Alais, Ivuna, Orgueil, Cold Bokkeveld and Nogoya. The data indicate the presence of two isotopically distinct major trapped components, components A and B. Two additional components, ‘C’ and ‘E,’ were isolated on the basis of neon isotopic structure. Components B and C, found in. gas-rich meteorites, are attributed to ion implantation by the present day solar wind and solar flares respectively. Component A is interpreted as a mixture of component E and component D (Paper I), where component D is identified with the primitive solar wind and component E is assigned an extra solar system origin.     

Hydrograph responses to geomorphic model watershed characteristics and precipitation variables

The primary objective of the Watershed Model Studies Project, reported herein, was to ascertain the effect of selected watershed characteristics on hydrograph parameters under a rainfall simulator. Since most of the runoff contributing to the peak flow was found to emanate from the lower half of the drainage, a measure of watershed eccentricity utilizing easily measured properties in that area is derived and evaluated as a reliable predictor of peak magnitude. In the process of isolating watershed shape, slope, size, drainage pattern, and soil depth were isolated and, along with rainfall intensity, direction of storm movement, and antecedent moisture conditions, evaluated for the models. Studies were made into the similarities between the models and real world watersheds. Three of the several conclusions are 1) the models exhibit hydrologic responses similar to those of a wide range of real watersheds; 2) watershed shape, of itself, does not have a tremendous effect on peak magnitude, and 3) watershed eccentricity is an effective, easily measured, meaningful, and useful expression of watershed shape insofar as that characteristic affects maximum peak flows and certain time parameters of the hydrograph.     

Chronology of Pliocene and Quaternary bioevents and climatic events from fission-track ages on tephra beds, Wairarapa, New Zealand

High-resolution Pliocene and Pleistocene sequences exposed on land in New Zealand are some of the few detailed records of widepread marine bioevents and paleoclimatic changes in the Southern Hemisphere. Marine biostratigraphy calibrated in deep-sea cores by paleomagnetic reversals has been the primary basis for the chronology of these sequences. We have determined ages for several tephra beds which now provide an independent numerical age calibration for a well-studied marine and terrestrial section in Wairarapa. By using the isothermal plateau fission track (ITPFT) method on volcanic glass we have overcome the problems of partial track fading and detrital mineral contamination, which hindered earlier studies, to reveal a new chronology extending back to nearly 5 Ma.

Our ages for the Hikawera Tuff (4.91 ± 0.25 Ma) and Spooner Tuff (3.44 ± 0.13 Ma) are consistent with the appearance and disappearance of many early Pliocene foraminiferial species, validating their age calibration in New Zealand. However, some fossil occurrences, including coccoliths, differ temporally by as much as 0.55 Ma, perhaps due to local tectonic-induced recycling.

Four Pleistocene tephra beds (Potaka tephra (1.00 ± 0.03 Ma), Kaukatea tephra (0.87 ± 0.05 Ma), Rangitawa tephra (ca. 0.35 Ma) and Kawakawa tephra (ca. 0.22 Ma)) are now recognised in the Wairarapa sequence via stratigraphic and new geochemical and age data. These beds allow direct correlation to other marine and terrestrial basins, as well as volcanic regions in New Zealand, and will ultimately aid in a regional paleoenvironmental reconstruction where bioevents are absent. The tephra ages indicate that the marine sediment accumulation rates varied from 90 to 250 m/Ma between different sections of the Pliocene and reached ca. 350 m/Ma in the last 2.4 Ma, when the sequence displays pronounced glacioeustatic cyclic deposition. In the terrestrial realm, the oldest loess in New Zealand is now constrained to between 1.00 and 0.87 Ma.     

The puzzle of high heads beneath the West Cumbrian coast,UK: a possible solution

A region of high heads within the Borrowdale Volcanic Group (BVG; a fractured crystalline rock) beneath the coastal plain of West Cumbria, England (UK), is identified as a possible relic left over by the Late Devensian ice sheet. It was found during investigations in the 1990s. Contemporary modelling work failed to produce a satisfactory explanation of the high heads compatible with the ‘cold recharge’ isotopic signature of the groundwater. This study has reassessed the original hydraulic testing results. By plotting density-adjusted heads versus their depth below the water table in the immediate vicinity of the borehole in which they were measured, a depth profile resembling a ‘wave’ was revealed with a peak value located at 1,100 m depth. The possibility that this wave represents relic heads from the last major ice sheet has been assessed using one-dimensional mathematical analysis based on a poroelastic approach. It is found that a wet-based ice sheet above the West Cumbrian coast was probably thick enough and sufficiently long-lasting to leave such relic heads providing that the hydraulic diffusivity of the BVG is in the order of 10^?6 m s^?1. Initial assessment 20 years ago of the long-interval slug tests suggested that such low values are not likely. More recent interpretation argues for such low values of hydraulic diffusivity. It is concluded that ice sheet recharge is the most likely cause of the raised heads, that the BVG contains significant patches of very low conductivity rock, and that long-interval single-hole tests should be avoided in fractured crystalline rock.     

E-ε modelling of turbulent air flow downwind of a model forest edge

A two-dimensional E- model, which included the effects of plant-atmosphere interaction, was used to simulate air flow downwind of forest edges for the purpose of predicting the microclimate in forest openings. A suitable set of wall functions was selected to consider the aerodynamic effects of the ground in the opening. The model with discretization and parameter schemes was validated using a set of data from a wind-tunnel experiment. The simulated wind speed and turbulence kinetic energy closely agreed with the measured values. After validation, the model was used to predict eddy diffusivity in the lee of the forest edge. The modelled spatial distribution of the eddy diffusivity agreed in general with that calculated using wind-tunnel measurements. The usefulness and limitations of the E- model are discussed.Presently with Intera Information Technologies Corporation, IMS Division, 2 Gurdwara Road, Nepean, Ontario, Canada K2E 1A2.Corresponding author, and presently with Canada Centre for Remote Sensing, 419-588 Booth Street, Ottawa, Ontario, Canada K1A 0Y7.     

Atmospheric turbulence within and above a Douglas-fir stand. Part I: Statistical properties of the velocity field

This is the first of two papers reporting the results of a study of the turbulence regimes and exchange processes within and above an extensive Douglas-fir stand. The experiment was conducted on Vancouver Island during a two-week rainless period in July and August 1990. The experimental site was located on a 5^o slope. The stand, which was planted in 1962, and thinned and pruned uniformly in 1988, had a (projected) leaf area index of 5.4 and a heighth=16.7 m. Two eddy correlation units were operated in the daytime to measure the fluctuations in the three velocity components, air temperature and water vapour density, with one mounted permanently at a height of 23.0m (z/h=1.38) and the other at various heights in the stand with two to three 8-hour periods of measurement at each level. Humidity and radiation regimes both above and beneath the overstory and profiles of wind speed and air temperature were also measured. The most important findings are:

1. A marked secondary maximum in the wind speed profile occurred in the middle of the trunk space (aroundz/h=0.12). The turbulence intensities for the longitudinal and lateral velocity components increased with decreasing height, but the intensity for the vertical velocity component had a maximum atz/h=0.60 (middle of the canopy layer). Magnitudes of the higher order moments (skewness and kurtosis) for the three velocity components were higher in the canopy layer than in the trunk space and above the stand.
2. There was a 20% reduction in Reynolds stress fromz/h=1.00 to 1.38. Negative Reynolds stress or upward momentum flux perisistently occurred atz/h=0.12 and 0.42 (base of the canopy), and was correlated with negative wind speed gradients at the two heights. The longitudinal pressure gradient due to the land-sea/upslope-downslope circulations was believed to be the main factor responsible for the negative Reynolds stress.
3. Momentum transfer was highly intermittent. Sweep and ejection events dominated the transfer atz/h=0.60, 1.00 and 1.38, with sweeps playing the more important role of the two atz/h=0.60 and 1.00 and the less important role atz/h=1.38. But interaction events were of greater magnitude than sweep and ejection events atz/h=0.12 and 0.42.

     

On the evolution of families of periodic orbits approaching a small primary

A network of families of periodic orbits is obtained approximately for the case =0.1 of the restricted problem using a direct grid search. Only such orbits of the third body are considered that cross the synodical line of the primaries outside the smaller of the two, perpendicularly, and in the direction of rotation of the system.