Oxygen and hydrogen isotope studies of serpentinization in the Troodos ophiolite complex,Cyprus

Oxygen and hydrogen isotopic compositions were measured on 12 serpentine and 2 actinolite samples from the Troodos ophiolite complex, Cyprus. The single analyzed antigorite(δD= ?60, δ¹⁸O= 7.1) is isotopically similar to all previously analyzed antigorites from ultramafic bodies. However, although their D/H ratios are relatively “normal”(δD= ?70to?92), the δ¹⁸O values of most of the Troodos lizardite-chrysotile serpentines (+12.6 to +14.1) are much higher than the 2.0–9.3‰ range typically found in such serpentines. Such high δ¹⁸O values have previously been found only in the serpentine-like mineraloids termed “deweylites”, which apparently formed at Earth-surface temperatures, and in a single sample from Vourinos, Greece that is in contact with high-¹⁸O limestone. The Troodos lizardite-chrysotile samplescannot have formed by reaction with heated ocean waters, but instead must have formed in contact with large amounts of some type of meteoric, metamorphic, or formation water, either (1) at very low temperatures in a near-surface environment, or (2) at about 100°C from waters that were abnormally enriched in¹⁸O(δ¹⁸O ≈ +4 to +8). The latter possibility seems most plausible inasmuch as extensive evaporites were deposited throughout the Mediterranean Sea during the late Miocene, and this would have been accompanied by strong¹⁸O enrichments of the local meteoric waters. Heated ocean waters, however, probably were responsible for the formation of the actinolitic amphiboles(δ¹⁸O= 4.6 to 5.5; δD= ?51to?46) from the gabbro and ultramafic zones in the Troodos complex. The amphiboles must have formed at considerably higher temperatures and at an earlier stage than the lizardite-chrysotile serpentinization.     

A model of atmospheric boundary-layer flow above an isolated two-dimensional ‘hill’; an example of flow above ‘gentle topography’

A numerical model is developed for two-dimensional turbulent boundary-layer flow above gentle topography — defined as not giving rise to mean flow separation. Although the model is formulated in a framework of mixing length and turbulent energy equation models for the surface layer of the atmospheric boundary layer, it could be modified to include higher-order closure hypotheses and/or extended to model gentle topography for the planetary boundary layer or on the sea bed. Results are presented for flow above a specific shape of hill and the effects of surface roughness and hill height are investigated.     

A contribution to the pseudoleucite problem

A study has been made of the differences produced in leucites by different methods of cooling charges, in the system NaAlSiO₄-KAlSiO₄-SiO₂-H₂O, consisting of leucite and silicate liquid. The results indicate that the ion exchange reaction in the system is so fast that metastable leucite-analcite solid solutions may be produced between leucite crystals and hydrous glass.     

The rare earth element geochemistry of granite,gneiss, and migmatite from the Western Metamorphic Belt of South-eastern Australia

Four muscovite-biotite granites from the Western Metamorphic Belt of South-eastern Australia have rare earth element patterns characterized by: (i) light rare earth element enrichment; (ii) slight Eu depletion; (iii) varying degrees of heavy rare earth element depletion. The rare earth element and major element chemistry of three of these muscovite-biotite granites (the Koetong, Lockharts and Yabba Granites) can be approximated very closely by a model involving 20% partial melting of an ultrametamorphosed pelitic sediment and contamination of this minimum melt by the residual material left after melting, in the ratio 60% melt: 40% residue. Granitoids can be very largely solid material at the time of emplacement.The other muscovite-biotite granite studied (the Hawksview Granite) has major and trace element characteristics which distinguish if from the other three granitoids and these differences are attributed to variations in source material at the site of melt generation.The rare earth element and major element chemistry of a garnet-cordierite gneiss from the Western Metamorphic Belt can be modelled assuming 5% partial melting of a pelitic metamorphic rock and contamination of the minimum melt by the residue in the ratio 30% melt: 70% residue.Separated granitic and biotitic portions of a migmatite from the Western Metamorphic Belt have rare earth element characteristics which are inconsistent with a simple partial-melting model, but it is suggested that re-equilibration following, or during, separation of the vein material could obscure the process by which the vein of the migmatite developed. It is however certain that the vein developed in situ from a pelitic meta-sediment leaving the biotite rich selvage, without the introduction of material from an external source.Leucogranites which crop out to the east of the Western Metamorphic Belt are high level intrusions of highly fractionated granitic melt. Their Sr isotopic characteristics and features of their major and trace element chemistry suggest that they derive from an igneous source and are not directly related to the granites and gneisses to the west.     

A note on ‘separation’ over short wind waves

Whether or not separation occurs in the airflow over wind-generated water waves is partly a question of semantics but also has an important bearing on the wave generation process. In the present paper we use a rather formal and perhaps narrow definition of separation and show that it does not occur where the shear stress is zero but only in conjunction with wave breaking. This is unlikely to happen except in the presence of quite strong surface drift velocities in the water. A similar connection between separation, surface drift and wave breaking has recently been established by Banner and Melville (1976).The effects of increasing wave amplitude or steepness are investigated with a numerical model of the airflow over water waves. Variations in the depth of the closed streamline region are predicted. The model is also used to investigate the possible importance of surface drift velocities.On leave 1976, Atmospheric Environment Service, Downsview, Ont., Canada.     

Numerical studies of neutrally stratified planetary boundary-layer flow above gentle topography

A numerical model of planetary boundary-layer flow above two-dimensional gentle topography is developed as an extension of the surface-layer model described by Taylor (1977). Comparisons are made with surface-layer predictions for flow over Gaussian hills; and the flow at various angles above hills, valleys and escarpments is modelled. Some simple case studies of the influence of gentle two-dimensional topography on pollutant dispersion are made which indicate relatively minor effects on surface pollutant concentrations in comparison with results for dispersion above a plane surface.     

High-18O igneous rocks from the Tuscan Magmatic Province,Italy

The ¹⁸O/¹⁶O ratios were measured for 60 rocks and coexisting minerals from the Plio-Pleistocene, calc-alkaline, Tuscan Magmatic Province, Italy. The ¹⁸O values of these magmas were as follows: Elba, Giglio, and Montecristo granodiorites (11.4 to 12.1); M. Cimini rhyolites and trachytes (11.2 to 11.7); Roccastrada, S. Vincenzo, and M. Amiata rhyolites (12.3 to 13.4); and the Tolfa rhyolites and quartz latites (15.3 to 16.4). The latter are by far the highest ¹⁸O values yet reported for primary volcanic rocks. The extremely high ¹⁸O values in the Tuscan Province indicate that these magmas all formed by melting or large-scale assimilation of high-¹⁸O argillaceous sedimentary rocks, in agreement with previous evidence based on the high ⁸⁷Sr/⁸⁶Sr ratios and ubiquitous presence of cordierite. Low ¹⁸O values (+5 to +6) were found in the feldspar, but not the quartz, of the small Porto Azzuro stock on Elba, as well as in the marginal facies of the M. Capanne stock, indicating that these bodies interacted with low-¹⁸O meteoric-hydrothermal fluids subsequent to solidification. The M. Cimini lavas apparently formed about 1 m.y. ago by mixing of high-¹⁸O Tuscan magmas containing large K feldspar crystals with potassic, undersaturated, low-¹⁸O magmas of the adjacent Roman Co-Magmatic Province. These large sanidine crystals did not completely equilibrate ¹⁸O/¹⁶O with the coexisting magma.Publication of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, Contribution Number 2639.     

Estimates of wind speed perturbation in boundary-layer flow over isolated low hills — Solutions

A computationally efficient model — the MS3DJH — was used to predict the near-surface wind-speed variations over a given idealised twin hill. Results given compare the model predictions with those of trained meteorologists. Further application of the model to assessment of e.g. power-producing turbine sites is discussed.     

The matrices of unequilibrated ordinary chondrites: Implications for the origin and history of chondrites

The matrices of sixteen unequilibrated ordinary chondrites (all witnessed falls) were studied microscopically in transmitted and reflected light and analyzed by electron microprobe. Selected specimens were also studied by scanning electron microscopy. These studies indicate that the fine-grained, opaque, silicate matrix of type 3 unequilibrated chondrites is compositionally, mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by Larimer and Anders (1967, 1970). Examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed, with the alteration ranging in intensity from quite mild, where the matrix has been only slightly altered, to a more severe metamorphism that has completely recrystallized the opaque matrix. Most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules. The metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves. The present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed, plus the subsequent metamorphic alteration it experienced.