Showing papers by "University of St Andrews published in 1975"

Curved branching crystals and differentiation in comb-layered rocks

Abstract: An investigation is conducted concerning two common features of comb layered rocks. Attention is given to the curvature of oriented, elongate, branching crystals and the tendency to form highly differentiated layers. Crystallization studies of plagioclase show that some degree of supercooling is necessary to produce the skeletal, curved, and branching plagioclase crystal morphologies found in comb-layered rocks and that curved crystals can be grown without the presence of a directed stress.

Age and origin of the Nigerian mesozoic granites: A Rb-Sr isotopic study

Abstract: Sixty-four Rb-Sr and two K-Ar isotopic measurements from seven ring complexes in central Nigeria provide evidence for a systematic age trend along a 200 km zone ranging from 174±5 m.y. in the north to 154±4 m.y. in the south. A peak of anorogenic magmatism occurred in the Jos Plateau region about 164±4 m.y. ago. Although a small syenitetrachyte complex at Zaranda, near Bauchi, gives an age of 190±15 m.y., unpublished ages of 290–330 m.y. for the southern Niger ring complexes confirm the existence of an overall southerly decreasing age trend in the Niger-Nigeria province of West Africa.

Hydrogen, carbon and oxygen isotope studies of megacryst and matrix minerals from lesothan and South African kimberlites

Abstract: Hydrogen carbon and oxygen isotope analyses were determined, where applicable, on phlogopite megacrysts (two samples), serpentine megacrysts (two), unweathered matrix (nine), carbonated granulite xenoliths (two), a carbonatite dyke and weathered yellow kimberlite from diatremes in Lesotho (Kao, Matsoku) and South Africa (Monastery, New Elands, Premier, Wesselton) and dykes and sills in Lesotho (Kaunyane) and South Africa (Benfontein, Du Plessis). The DH ratios of phlogopite megacrysts are in the range previously reported for possible upper mantle derived phlogopites: −40 to −70 per mil, SMOW. DH ratios of the serpentinized megacrysts and the hydrous phases of the matrix, dominantly serpentine and/or phlogopite, are depleted in D by 20 to 55 per mil relative to the phlogopite megacrysts from, in some cases, the same sample. Serpentine megacrysts and serpentine-rich matrix samples are depleted in 18O by up to 6 per mil relative to both phlogopite-rich and olivine-rich matrix, and “normal” ultramafic values. The H- and O-isotope data indicate that meteoric-hydrothermal fluids interacted with the kimberlite during the major serpentinization processes. The origin of fluids associated with matrix phlogopite cannot be defined specifically: magmatic, metamorphic or exchanged meteoric waters with very low water/rock ratios (< 0.2 at.% oxygen) or some combination are possible. The isotopic “thermometers” indicate very approximately that the matrix phlogopite crystallized at temperatures on the order of 200° to 500°C and serpentinization process occurred at 50° to 200°C. Carbonates from the matrix, carbonatite dykes and xenoliths have δ18O = +7 to +21 per mil, SMOW and δ13C = −3 to −7.5 per mil, PDB. The C-isotope ratios are similar to those for most diamonds and primary igneous carbonatites and are similarly variable at a single locality. They are compatible with a genetic relationship among these carbon sources. The 18O enrichment of most kimberlite carbonates is a result of the relatively low temperature of exchange with other matrix minerals and/or with meteoric-hydrothermal fluids. Loss of CO2 + H2O fluid during degassing may contribute to the H- and C-isotope variations in a kimberlite. The water content of kimberlite magmas were probably substantially less than the 5 to 10 wt.% H2O observed in many diatreme-facies kimberlites. The preservation of diamonds in a kimberlite may be critically dependent on both the initial water content of the mell and the stage and temperature at which large-scale influx of ground waters into the kimberlite occured. Weathered yellow kimberlite is isotopically distinctive from our matrix samples.

Occurrence of diamond in a mica–garnet Iherzolite xenolith from kimberlite

Abstract: ALTHOUGH graphite has previously been reported from upper-mantle garnet lherzolite xenoliths from kimberlite intrusions, diamond has not previously been found in upper-mantle garnet lherzolite xenoliths from kimberlite intrusions. Diamond of primary terrestrial origin is found mainly in the rare ultramafic, potassic rock, kimberlite. Although the precise source of most diamonds in kimberlite is unknown it is generally assumed that most of the diamonds originate from the kimberlite matrix itself. A few have, however, been found enclosed in eclogite xenoliths of widely varying composition1–3 and also in rare xenoliths of garnet serpentinite from the Aykhal kimberlite diatreme in Siberia4. We report here on the occurrence of diamond in a xenolith of garnet lherzolite, the material generally believed to dominate the Earth's upper mantle on density, seismic and experimental grounds.

The preparation of nylon-tube-supported hexokinase and glucose 6-phosphate dehydrogenase and the use of the co-immobilized enzymes in the automated determination of glucose.

Abstract: Triethyloxonium tetrafluoroborate was used to O-alkylate nylon-tube thus producing the imidate salt of the nylon which was further made to react with 1,6-diaminohexane. 2. Hexokinase (EC 2.7.1.1) and glucose 6-phosphate dehydrogenase (EC 1.1.1.49) were immobilized on the amino-substituted nylon tube through glutaraldeyde and bisimidates. 3. The effect of varying the conditions of O-alkylation and the amount of enzyme immobilized on the activity of nylon tube-hexokinase derivatives was determined. 4. The effect of varying the amount of enzyme immobilized on the activity of nylon-tube-glucose 6-phosphate dehydrogenase derivatives was determined. 5. The thermal stability of nylon-tube-hexokinase and nylon-tube-glucose 6-phosphate dehydrogenase derivatives was studied. 6. Different ratios of hexokinase and glucose 6-phosphate dehydrogenase were co-immobilized on nylon tube, and the rate of conversion of glucose into 6-phosphogluconolactone was compared with the individual activities of the immobilized enzymes. 7. Hexokinase and glucose 6-phosphate dehydrogenase co-immobilized on nylon tube were used in the automated analysis of glucose.

Thallium: occurrence in the environment and toxicity to fish.

Abstract: Thallium is present in the effluents of the base-metal mining industry, and its acute toxicity to juvenile Atlantic salmon is approximately equal to that of copper. The usual treatment of waste water with alkali to remove heavy metals by precipitation has little effect on thallium. The limited use of thallium will not lead to a global contamination of the environment, but localized problems may exist or develop in the future, mainly as a result of mineral processing.

Preflare Current Sheets in the Solar Atmosphere

Abstract: Neutral current sheets are expected to form in the solar atmosphere when photospheric motions or the emergence of new magnetic flux causes oppositely directed magnetic fields to be pressed together. Magnetic energy may thus be stored slowly in excess of the minimum energy associated with a purely potential field and released suddenly during a solar flare. For simplicity, we investigate the neutral sheet which forms between two parallel line dipoles when either the distance between them decreases or their dipole moments increase. It is found that, when the dipoles have approached by an amount equal to a tenth of their original separation distance, the stored energy is comparable with that released in a major flare. In addition, a similarity solution for one-dimensional magnetohydro-dynamic flow within such a neutral sheet is presented; it demonstrates that rapid conversion of magnetic energy into heat is possible provided conditions at the edge of the neutral sheet are changing sufficiently quickly.

A sample holding technique for study of crystal growth in silicate melts

Abstract: A thin platinum wire loop is an effective way to hold silicate melts during experimentation in a gas-mixing furnace. This method results in a minimum of physical and chemical interaction between the sample and container but maximum interaction between sample and gas mixture. However, volatilization of sodium occurs while the silicate is molten. By minimizing the chance of heterogeneous nucleation, the method is ideal for experimental investigation of the origin of rock textures.

Mineral chemistry of peridotite xenoliths from the Lashaine volcano, Tanzania

Abstract: Eight garnet peridotite and ten garnet-free peridotite xenoliths from the Lashaine volcano in northern Tanzania, and one garnet peridotite from the Matsoku pipe in Lesotho, were studied petrographically and by electron-microprobe techniques. The primary assemblages are ol + opx + cpx + ga, ol + opx + cpx + chr, ol + opx + ga + chr, ol + opx + ga, ol + opx + chr, and ol + cpx + chr. With the exception of the ol + cpx + chr assemblage, which is more iron-rich, the composition of each of the primary mineral species is essentially the same for all the xenoliths and is independent of the abundances of the minerals. The primary minerals are Ni-rich very low Ca olivine (Fo92), low Ca, Al, Cr, Ti, Mn,enstatite (Wo1En93Fs7), low Al, Ti, Mn chrome diopside (WO44En52Fs4), chrome pyrope and Mg, Al-rich chromite. Comparisons with phase equilibria studies suggest that the primary assemblages are stable at approximately 1050°C and 50 kbar, equivalent to a depth of approximately 150 km. The primary xenolith assemblages have been locally altered by three types of secondary processes. (1) Garnet has reacted with the adjacent olivine to produce reaction rims of aluminous orthopyroxene plus aluminous clinopyroxene plus spinel. (2) Some chrome-diopsides show marginal or total alteration that may result from secondary melting. (3) Extremely localized partial melting has occurred at some grain boundaries and the interstitial melt quenched to various combinations of olivine, clinopyroxene, orthopyroxene, spinel, phlogopite and glass. Garnet-bearing and garnet-free assemblages differ in bulk composition but have formed under similar physical conditions. The xenoliths derive from a region of the upper mantle that is homogeneous in terms of mineral compositions but heterogeneous, at least on the scale of the Lashaine xenoliths, in mineral proportions and bulk composition. Phlogopite in one garnet peridotite appears to be primary and several peridotites contain regions that have formed by localized melting of K-rich areas. Either the peridotites are not refractory residues from partial melting in the mantle or K-rich material has been added to them after partial melting but within the mantle, before incorporation into the ankaramite host.

Correlation between the breeding system and recombination index in five species of senecio

Abstract: SUMMARY The species Senecio aetnensis Jan., S. joppensis Dinsm., S. squalidus L., S. viscosus L. and S. vulgaris L. have been compared for automatic selfing ability, capitulum conspicuousness, pollen yield, chromosome number and chiasma frequency. It has been established that the species S. aetnensis, S. joppensis and S. squalidus which have low automatic selfing ability have large, showy capitula, high pollen output and low recombination indices. The species S. viscosus and S. vulgaris which have a high selfing ability have relatively inconspicuous capitula, low pollen yields and a high recombination index. The differences in recombination index values are mainly due to the fact that the selfing species are polyploids but it may be significant that the highest average chiasma frequencies per bivalent were found in some S. vulgaris plants. The adaptive significance of a high recombination index in inbreeding taxa is discussed and it is suggested that a high chiasma frequency and/or polyploidy may have a preadaptive value in facilitating the change from outbreeding to inbreeding in some species.

Neuromuscular control of ventilation in the crabCarcinus maenas

Abstract: (1) The musculoskeletal system and innervation of the scaphognathite (SG) of the second maxilla inCarcinus maenas are described. Rhythmic beating of the SG is effected by ten muscles subdivided into two main sets, five levators and five depressors, and further, into four groups designated D1 and D2 (depressors) and L1 and L2 (levators). Sequential activation of the groups of muscles results in trapezoidal movements of the anterior and posterior tips of the SG, about 180° out of phase, and roughly sinusoidal movement of the middle (hinge) region, resulting in efficient pumping of water (Fig. 11). (2) The SG can pump water either in the forward or the reversed direction. During forward pumping the sequence of recruitment of the groups is D1, D2, L1, L2... During reversed pumping, the muscles remain grouped as in forward pumping but the recruitment sequence is inverted: L2, L1, D2, D1, L2... At the onset of reversal the group D2 forward mode units are suppressed and replaced during the subsequent reversed cycles by a different set of reversed mode units to the D2 muscles (Fig. 14). (3) Peak bursting frequencies in muscles from the same group are roughly synchronous in both beat modes, while peaks for muscles from different groups alternate in such a way as to suggest synchronizing or positive interactions between units in the same group and negative interactions between units from temporally adjacent groups. (4) Spike train analyses suggest direct interactions between units both from the same group and from different groups among the depressor muscles, but these perhaps, do not contribute towards organizing the main features of the output pattern. (5) The durations of the whole levator and depressor sessions, durations of the bursts in the various muscles, and latencies between the starts of bursts in muscles from temporally adjacent groups all show strong, positive, linear correlation with period length. The motor output pattern is essentially phase constant but latencies between the starts of bursts in muscles from the same group are very weakly or not at all correlated with period length, suggesting that within group timing is less directly related than between group timing, to activity in the pacemaking oscillator (Mendelson, 1971) which drives the reciprocating motor activity of the SG. (6) The present findings, along with the other available data on the SG motor system suggest a tentative, hierarchical model for the SG “motor programme”, in which the main features of the motor output pattern, including reversals, are proposed to arise through interactions at premotoneuronal levels (Fig. 16).

Major and trace element chemistry of peridotite inclusions from the Lashaine volcano, Tanzania

Abstract: Whole rock analyses and selected trace element data are reported for nineteen, extremely fresh, peridotite xenoliths, together with the host ankaramite and associated carbonatite tuff, sampled from the Lashaine volcano in northern Tanzania. For comparison, data for a garnet peridotite from Matsoku in eastern Lesotho are included. These xenoliths are inferred to be derived from the garnet peridotite zone of the upper mantle from depths of about 150 km. The chemical data indicate that, despite considerable compositional heterogeneity, two distinct groups of peridotite inclusions have been sampled. One group, the garnet peridotites, are distinguished from the other group, the garnet-free peridotites, by higher concentrations of Al 2 O 3 (> 1%) and lower amounts of MgO ( 2 , CaO, Na 2 O, K 2 O, Cr 2 O 3 , Rb, Y, Zr and Nb, and higher Rb Sr ratios in the garnet peridotites than in the garnet-free rocks. Evidence is presented which indicates that the peridotite inclusions are accidental, and are genetically unrelated to the ankaramite host. It is also shown that in contrast with similar inclusions in kimberlite, most of the Lashaine inclusions have not been substantially contaminated by the host rocks. Consequently, the compositions of these inclusions are pertinent to questions concerning the composition of the upper mantle. In comparison with available data for peridotite inclusions and inferred mantle compositions, the Lashaine inclusions appear to be derived from residual mantle material. However, the K and Rb concentrations are at variance with this interpretation, since they are substantially higher than is typical for most uncontaminated peridotite inclusions, and would necessitate unacceptably high concentrations of these elements in the primary, undepleted material. Two interpretations are advanced: either the Lashaine garnet peridotite inclusions are themselves samples of relatively undepleted primary mantle material, or they are samples of depleted residual material that has been contaminated at or close to the source, prior to incorporation in the ankaramite magma.

Lithophile trace element data bearing on the origin of peridotite xenoliths, ankaramite and carbonatite from Lashaine volcano, N. Tanzania

Abstract: Rare-earth elements (REE) Rb, Sr and Ba have been determined in three garnet peridotites and a spinel peridotite that occur as xenoliths in ankaramite at Lashaine volcano. These element data have also been determined for the ankaramite and a closely associated carbonatite. Three peridotites have light REE-fractionated patterns, variable Rb, Sr and Sr 87 Sr 86 values which are consistent with mixing of peridotite with ankaramite. However, bulk contamination by either ankaramite or carbonatite is inconsistent with other major and trace element data. Remaining alternatives are selective elemental transfer between xenolitha and host or contamination within the mantle prior to incorporation within the ankaramite/carbonatite magma. The ankaramite has a highly fractionated REE pattern but is less enriched in lithophile trace elements than many alkalic rocks. The carbonatite has a fractionated pattern, but is significantly depleted in large ion lithophile elements compared to most other igneous carbonatites. Single-stage melting of mantle material is unlikely to have produced the carbonatite, and derivation of the carbonatite from a carbonated ankaramite magma requires substantial fractionation of some lithophile trace elements into the carbonatite and others into the ankaramite.

The Igwisi Hills extrusive “kimberlites”

Abstract: The petrography and mineral chemistry of volcanic rocks from the Igwisi Hills in Tanzania are discussed. There is considerable evidence to suggest that the Igwisi rocks are extrusive kimberlites: a two-component nature with high P-T minerals in a low P-T matrix; the presence of chrome pyrope, Al enstatite, chrome diopside, chromite and olivine; a highly oxidized, volatile-rich matrix with serpentine, calcite, magnetite, perovskite; high Sr, Zr, and Nb contents; occurrence in a narrow isolated vent within a stable shield area. The Igwisi rocks differ from kimberlite in the lack of magnesian ilmenite, the scarcity of matrix phlogopite, and the overall low alkali content. They apparently contain material from phlogopite-bearing garnet peridotites with a primary mineral assemblage indicative of equilibrium at upper mantle temperatures and pressures. This primary assemblage was brought rapidly to the surface in a gas-charged, carbonate-rich fluid. Rapid upward transport, extrusion, and rapid cooling have tended to prevent reaction between inclusions and the carbonate-rich matrix that might otherwise have yielded a more typical kimberlite.

Chemistry and origin of phlogopite megacrysts in kimberlite

Abstract: STUDIES of the megacrysts occurring in kimberlite have hitherto neglected the mica megacrysts. We have analysed mica megacrysts from one Lesotho and twelve South African kimberlites. The megacrysts, which vary in size from 4 mm to 3 cm, were taken from both ‘basaltic’ and micaceous kimberlites, and distinguished from the matrix phlogopites by (i) their greater size; (ii) their dark brown, rather than bronze or light brown, colour; (iii) their rounded shape and corroded margins; (iv) distortion of the {001} planes (in some, but not all, megacrysts); and (v) absence of inclusions of matrix phases such as perovskite and spinel which often occur in the matrix micas.

Progress of migrating Atlantic salmon (Salmo salar) along an estuary, observed by ultrasonic tracking

Abstract: Adult Atlantic salmon were captured in the Miramichi esturary, tagged with ultrasonic transmitters, and released. Nine fish were tracked for a total of 425 h, spanning 71 flood and ebb tides. There was drifting with the tidal currents, and holding of position relative to land. Fish that achieved overall upstream progress did so by drifting with flood tidal currents and by stemming the ebb currents. Fish which did not achieve upstream progress also drifted with flood tidal currents, but these fish did not stem the ebb currents and dropped back downstream during ebb tides. No differences in movement patterns were apparent for different times of day or wind conditions.

The mandibular organ of the lobster, Homarus americanus.

Abstract: The lobster mandibular organ is well vascularized and its polygonal cells are arranged loosely around blood vessels and blood sinuses. Numerous mitochondria and microbodies (peroxisomes) give the acidophilic cytoplasm a finely granular appearance, but there is no evidence of secretory granules. The abundant endoplasmic reticulum is almost entirely agranular and occurs in two morphologically distinct forms: tubular and cisternal. The tubular reticulum is randomly distributed and may represent the site of synthesis and transport of the mandibular organ product. The cisternal reticulum is frequently associated with microbodies. Both forms of endoplasmic reticulum proliferate during mid to late premolt. Mandibular organ ultrastructure closely resembles that of cells known to synthesize steroids or lipids, which suggests that this organ may have a similar function. There is no functional evidence of involvement in molt control in Homarus, but ultrastructural and other evidence suggests an analogy with the insect corpus allatum.