The Royal Society
0080-4614
2054-0272
Cơ quản chủ quản: N/A
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Các bài báo tiêu biểu
Chemical variations in upper mantle nodules from southern African kimberlites A summary of the rock and mineral nodules erupted with kimberlites is presented. Garnet-peridotites are separated into various categories according to: their relatively depleted and fertile chemical character; their deformed and undeformed nature; and the Ca/(Ca + Mg) ratio of their clinopyroxenes (with associated temperature characteristics). Some bulk chemical similarities are noted between high-temperature, deformed and less depleted peridotites and the wall rocks to minor intrusions. There is clear evidence of the occurrence of infiltration metasomatism (involving K, Ti and other incompatible elements) in some mantle xenoliths before their incorporation in the kimberlite. These metasomatic effects may be linked with earlier magmatic events. Extreme chemical heterogeneities may be produced by metasomatism, as with restricted partial melting. Attempts to find homogeneous rocks with average or pristine upper mantle compositions are considered unrealistic. Within the Kaapvaal craton there is no overall pattern of lateral variations in the nodule types from kimberlite, though there is evidence of local heterogeneity and regional changes at craton margins. Boyd & Nixon’s models of vertical layering of rocks and minerals in the upper mantle are contrasted with a model in which horizontal variations in temperatures occur after magma intrusion. It is suggested that the high-temperature deformed peridotites and the megacrysts result from the intrusion of high-temperature magmas into overlying cooler mantle, and that xenoliths from kimberlite provide little direct evidence of mantle stratification with depth.
Tập 297 Số 1431 - Trang 273-293 - 1980
Chemical heterogeneity and metasomatism in the upper mantle: evidence from rare earth and other elements in apatite-rich xenoliths in basaltic rocks from eastern Australia
Apatite-rich inclusions in some basaltic rocks from eastern Australia are interpreted as mantle crystallization products of a carbonatitic/kimberlitic fluid enriched in low atomic number rare earth elements (l.r.e.e.), and are
a priori
evidence for mantle heterogeneity. The chondrite-normalized rare earth abundances of separated apatite, clinopyroxene, amphiboles and micas are high, with La in apatite being up to 4600 times chondrite. Apatites show a significant variation in rare earth content and in La:Lu ratios, indicating the occurrence of some crystal fractionation. The absence of europium anomalies from all mineral phases is indicative of a relatively high oxygen fugacity for the parent magma. The nature of the rare earth element distribution between mineral pairs suggests that some xenoliths represent equilibrium assemblages while some of the amphibole-bearing ones do not. The fluid from which these xenoliths crystallized would be an ideal agent for the metasomatism of upper mantle material and may account for l.r.e.e. enriched patterns of primary magmas in some alkaline provinces.
Tập 297 Số 1431 - Trang 333-346 - 1980
The fit of the continents around the Atlantic The geometrical fit of the continents now separated by oceans has long been discussed in relation to continental drift. This paper describes fits made by numerical methods, with a ‘least squares’ criterion of fit, for the continents around the Atlantic ocean. The best fit is found to be at the 500 fm. contour which lies on the steep part of the continental edge. The root-mean-square errors for fitting Africa to South America, Greenland to Europe and North America to Greenland and Europe are 30 to 90 km. These fits are thought not to be due to chance, though no reliable statistical criteria are available. The fit of the block assembled from South America and Africa to that formed from Europe, North America and Greenland is much poorer. The root-mean-square misfit is about 130 km. These geometrical fits are regarded as a preliminary to a comparison of the stratigraphy, structures, ages and palaeomagnetic results across the joins.
Tập 258 Số 1088 - Trang 41-51 - 1965
A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - The evolution of the Gulf of Aden
Marine geological and geophysical data from the International Indian Ocean Expedition, especially from cruise 16 of R. R. S.
Discovery
, have made it possible to prepare new charts of the bathymetry and the magnetic anomaly field which, together with other data, enable the evolutionary history of the Gulf of Aden to be worked out. Over the past 10 Ma the theory of seafloor spreading can account satisfactorily for the features of the Sheba Ridge and provides evidence of spreading rates in the direction of the fracture zones varying from 0.9 cm a
-1
per limb in the west to 1.1 cm a
-1
per limb in the east. Between the initial creation of the Gulf and 10 Ma ago, the evolution is less certain, although the geophysical evidence indicates that the crustal structure of the Gulf outside the Sheba Ridge is oceanic.
Tập 267 Số 1181 - Trang 227-266 - 1970
The wakes of cylindrical bluff bodies at low Reynolds number Experiments on the near wake of a cylinder will be discribed in an attempt to present a coherent picture of the events encountered as the Reynolds number increases from small values up to values of a few thousand. Much work on this subject has already been done, but there are gaps in our description of these flows as well as more fundamental deficiencies in our understanding of them. The subject has been reviewed several times and most recently by Berger & Wille (1972) whose paper covers much of the ground that will be discussed again here. The present work may be regarded as built upon this latest review. I remember with gratitude many helpful discussions with the late Rudolph Wille who contributed so much to this subject. The investigation has concentrated on circular cylinders, but the wakes of bluff cylinders of different cross sectional shapes have also been observed. Bluff cylinders in general are considered in §§4 and 5, together with the effect of splitter plates on circular cylinders in §9. The experiments concern, almost exclusively, flow visualization of the wakes by means of dye washed from the bodies. The patterns of dye observed are, therefore, filament line representations of the flow leaving the separation lines on the body. It must be stressed that the dye does not make visible the vorticity bearing fluid because at low Reynolds number, vorticity diffuses considerably more rapidly than does dye. The ratio of the molecular diffusivity of momentum to that of mass of dye is of the order of 100.
Tập 288 Số 1354 - Trang 351-382 - 1978
Interface in composite materials The mechanical characteristics of a fibre-resin composite depend primarily on the mechanical properties of the combined materials, the surface of the fibre, the nature of the fibre-resin bonding as well as the mode of stress transfer at the interface. These two last points are related to the surface properties of the fibres. The various types of bonding that may occur between fibrous materials (carbon, glass and organic fibres) and organic polymers, including the relevant theories, are briefly reviewed. In order to optimize the fibre-resin interactions, it is often essential that the interface should be chemically modified. The various possible treatments may be classified under three headings: chemical surface modification of the fibre, sizing and polymer fixation (grafting). The major factors that influence the interactions between high-performance fibres and organic resins will be established and discussed, as illustrated in a few selected examples.
Tập 294 Số 1411 - Trang 495-505 - 1980
Multispectral remote sensing for the estimation of green leaf area index The causal relation between multispectral reflectance and green leaf area index (l.a.i.) has enabled the estimation of green leaf area index by the judicious use of remotely sensed multispectral reflectance measurements. In this paper three topics are discussed. First, the reflectance properties of a vegetation canopy and the problems of determining the form of the relation between green l.a.i. and red and near-infrared reflectance: these problems include variability in substrate and leaf reflectance and the geometry of the scene and sensor. Second, the methodologies currently employed for estimating green l.a.i.: these methodologies are based on the production of simple, complex or modelled calibration curves. Third , current research at the University of Sheffield: this includes not only studies with multispectral reflectance collected from aircraft-mounted sensors to estimate the green l.a.i. of heathlands and grasslands but also multispectral reflectance collected from satellites to map estimated green l.a.i. It is concluded that the main applications for this remote-sensing technique are within the fields of agricultural intelligence, agricultural m anagement and ecological research.
Tập 309 Số 1508 - Trang 257-270 - 1983
Geomagnetic secular variation from <sub>14</sub> C-dated lava flows on Hawaii and the question of the Pacific non-dipole low New palaeomagnetic data from 106 14C-dated lava flows ranging in age from 200 to 31000 years b.p. yield an estimated angular dispersion value of 9.5°. These data and other new geological information permit a more precise estimate of the time interval recorded by lava flow sequences previously used to measure palaeosecular variation in Hawaii. When weighted according to revised estimates of recording interval, the combined Brunhes lava sequences yield an angular dispersion of 11.21));j) degrees, still lower than that predicted by global models of the secular variation. Several of the lava flow sequences previously thought to have recorded quiet intervals of geomagnetic behaviour actually record only very short time intervals.
Tập 306 Số 1492 - Trang 211-222 - 1982
Light scattering in the study of dynamical properties Motion in many forms may be studied by light scattering. On one extreme this may be the bulk motion of a large target such as a vehicle or a satellite; on the other it may be the diffusional motion of an atom or molecule. The paper will outline the basic principles involved in such measurements and introduce the mathematical apparatus required to derive spectra of the scattered light. This can be couched in terms of speckle and Doppler shifts in the first case, while for molecular systems in thermodynamic equilibrium, we need a form of modern many-body theory. With this we calculate dynamical mode correlations as functions of the transport coefficients of irreversible thermodynamics. Examples will be given in the measurement of flow and turbulence, marcromolecular diffusion and polydispersity, and molecular scattering, including mode-mode coupling effects in condensed matter.
Tập 293 Số 1402 - Trang 349-358 - 1979
The study of Brownian motion by intensity fluctuation spectroscopy
The principles and methods of quasielastic light scattering and intensity fluctuation spectroscopy (i.f.s.) are reviewed briefly. Their application to the study of Brownian motion is discussed with emphasis on the behaviour of the velocity autocorrelation function
ϕ
(
τ
) of a single particle. We consider: (i) The situation usually assumed where
ϕ
(
τ
) decays rapidly compared with other timescales of interest; (ii) the modification of (i) due to the τ
-3/2
‘long-time tail’ in
ϕ
(
τ
) including the recent i.f.s. experiment of Boon & Bouiller (1976) which confirms its existence, and finally (iii) systems of charged colloidal particles exhibiting 'liquid-like’ spatial ordering due to long-range Coulombic interactions. Here
ϕ
(
τ
) has a
negative
long-time tail. We also consider the many-body dynamics in these systems by exploiting the similarity with neutron scattering by simple atomic liquids. ‘Solid-like’ systems are discussed briefly.
Tập 293 Số 1402 - Trang 429-439 - 1979