Showing papers by "Open University published in 1986"

Geochemical characteristics of collision-zone magmatism

Abstract: This paper reports the results of a systematic geochemical study of intermediate and acid intrusive rocks from a number of continent-continent collision zones of Phanerozoic age. Four groups of intrusions can be recognized, each associated with a particular stage in the tectonic evolution of a collision zone. Pre-collision calc-alkaline (volcanic-arc) intrusions which are mostly derived from mantle modified by a subduction component and which are characterized by selective enrichments in LIL elements. Syn-collision peraluminous intrusions (leucogranites) which may be derived from the hydrated bases of continental thrust sheets and which are characterized by high Rb/Zr and Ta/Nb and low K/Rb ratios. Late or post-collision calc-alkaline intrusions which may be derived from a mantle source but undergo extensive crustal contamination and can only be distinguished from volcanic-arc intrusions by their higher ratios of Ta/Hf and Ta/Zr. Post-collision alkaline intrusions which may be derived from mantle lithosphere beneath the collision zones and which carry high concentrations of both LIL and HFS elements. The geochemical evolution of crustal melts within groups (ii) and (iii) can be viewed in terms of the dehydration reactions, volatile transfer and transient geothermal gradients that result from thrust tectonics in the zone of collision.

The Problem of Ideology-Marxism without Guarantees:

Abstract: In the past two or three decades, marxist theory has been going through a remarkable, but lop-sided and uneven revival. On the one hand, it has come once again to provide the principal pole of opposition to &dquo;bourgeois&dquo; social thought. On the other hand, many young intellectuals have passed through the revival and, after a heady and rapid apprenticeship, gone right out the other side again. They have &dquo;settled their accounts&dquo; with marxism and moved on to fresh intellectual

Evidence from the Parana of south Brazil for a continental contribution to Dupal basalts

Abstract: It has been suggested1,2 that the oceanic upper mantle preserves a large scale isotope anomaly, Dupal2, which may be thousands of millions of years old. New Nd-, Pb- and Sr-isotope data on the continental volcanic rocks of the Parana, south Brazil, reveal ‘enriched’isotopic ratios, with 87Sr/86Sr = 0.705−0.716 and end = −2.5 to −8, similar to those from other continental flood basalt provinces. Their 207Pb/204Pb ratios are higher than those of mid-ocean-ridge basalts (MORB) at comparable 206Pb/204Pb, and even though the basalts appear to have been derived from lithospheric sources within the sub-continental mantle, they preserve isotope and trace element ratios similar to those in oceanic basalts with the Dupal signature in the South Atlantic. The implied link between these continental flood basalts and Dupal oceanic volcanics raises the possibility that in some areas the Dupal anomaly marks a comparatively shallow-level feature in the Earth's mantle.

Memory for proper names: age differences in retrieval

Abstract: Memory for proper names was investigated using (i) a questionnaire and (ii) an experimental task. Subjects ranging in age from 20 to 80 years recorded details of naturally occurring retrieval blocks for proper names. Age differences in the nature of the blocks were apparent. For the young and middle-aged partial information about the target name was usually available and non-target candidates were elicited during search for the target name. Elderly subjects more frequently experienced an ‘empty gap’, with no partial information about the target name and no candidate names. The experimental task required recall of names and descriptions from specially constructed fictional biographies. There was an age-related deficit in recall of all types of information, but in all age groups memory for names of people was poorer than memory for names of places, occupations and hobbies. Some explanations for the difficulty of retrieving people's names and for the age effects are considered.

Precambrian collision tectonics in Africa

Abstract: Summary Stages of the collisional process are separated. Criteria are proposed by which A- and B-subduction may be distinguished. Late Precambrian structures in NE Africa are attributed to successive gentle collisions of island arcs; the sutures dip E or SE and relative plate motion was NW-SE. In the polycyclic Proterozoic Mozambique Belt of E Africa there are probably three sutures (Sekerr, Baragoi, Moyale-Shakiso) with ophiolites; they appear to dip E. It is argued that despite the lack of geochronological evidence, Archaean basement probably underlies the metasedimentary sequences, right across the Mozambique Belt of E Africa, from the Archaean Tanzania Craton on the W to the Archaean Craton, represented by Madagascar and S India, on the E. The belt is therefore interpreted as having been built by collision of continental plates. Widespread recumbent structures, complex and intense deformation and high-grade metamorphism imply crustal thickening and a multistage collisional history. Relative NW-SE motion was probably followed by N-S post-collisional ductile shear. The Archaean Limpopo Belt in southern Africa shows evidence of drastic crustal thickening and intense deformation in contrast to the much weaker deformation and little crustal thickening in the Kaapvaal and Rhodesian Cratons to the S and N. Collision is implied but in the absence of convincing ophiolites, subduction-type calc-alkaline magmatism and abyssal sediments, B-subduction remains unproven.

The Becker-Döring cluster equations: basic properties and asymptotic behaviour of solutions

Abstract: Existence and uniqueness results are established for solutions to the Becker-Doring cluster equations. The density ϱ is shown to be a conserved quantity. Under hypotheses applying to a model of a quenched binary alloy the asymptotic behaviour of solutions with rapidly decaying initial data is determined. Denoting the set of equilibrium solutions byc (ϱ), 0 ≦ ϱ ≦ ϱ s , the principal result is that if the initial density ϱ0 ≦ ϱ s then the solution converges strongly toc (ϱo), while if ϱ0 > ϱ s the solution converges weak* toc (ϱs). In the latter case the excess density ϱ0–ϱ s corresponds to the formation of larger and larger clusters, i.e. condensation. The main tools for studying the asymptotic behaviour are the use of a Lyapunov function with desirable continuity properties, obtained from a known Lyapunov function by the addition of a special multiple of the density, and a maximum principle for solutions.

Preliminary conclusions of the Royal Society and Academia Sinica 1985 geotraverse of Tibet

Abstract: The 1985 Chinese/British expedition to the Tibetan Plateau attempted to solve the question of the origin of the very thick crustal rocks in this region. Continuing northwards movement of the Indian plate over the past 38 Myr has given rise to severe folding and thrust faulting, causing crustal thickening by internal deformation. Previous collisions of microplate terranes derived from Gondwanaland occurred during Mesozoic times but the Kun Lun terrane of northern Tibet was already part of Laurasia by the Carboniferous

Coupled trace element and isotope enrichment in the Cook-Austral-Samoa Islands, Southwest Pacific

Abstract: Combined Pb-Sr-Nd isotope and trace element data are presented for eight islands within the Cook-Austral-Samoa island archipelago, southwest Pacific. These data reveal the presence of two geochemically distinct components within the OIB mantle. The Mangaia component represented by the islands of Mangaia and Tubuai has extremely radiogenic Pb isotopes but low87Sr/86Sr . A Dupal component represented by Samoa has high87Sr/86Sr , with low Pb ratios which are enriched in207Pb and208Pb. Nd isotope ratios of the Dupal component are slightly lower than for Mangaia. The Dupal isotope enrichment is coupled with high LIL/HFS element ratios relative to Mangaia. The Mangaia isotope enrichment is associated with low LIL/HFS element ratios comparable with or lower than MORB and indicates a time-integrated depletion in LIL elements in the source. However, inferred low ThU , and PbNb ratios indicate that Mangaia has been enriched in U but depleted in Pb relative to MORB. It is suggested that Mangaia could be derived from hydrothermally altered, subducted MORB. The Dupal component may include recycled subcontinental lithosphere.

Geochemistry of bimodal basalt-subalkaline/peralkaline rhyolite provinces within the Southern British Caledonides

Abstract: Bimodal associations of basalt and rhyolite of Upper Ordovician age which were erupted in a submarine environment occur within the Caledonian orogenic belt of South Britain at Parys Mountain (Anglesey), in Snowdonia (North Wales) and at Avoca (SE Ireland). The volcanic rocks have experienced hydrothermal alteration and low-grade metamorphism, and therefore immobile elements (e.g. Ti, Zr, Nb, Y) have been used to identify the original geochemical characteristics. The basalts have characters transitional between volcanic ‘arc’ and ‘within plate’ types consistent with eruption on an extensional part of an active continental margin. Two groups of rhyolites have been identified. A low-Zr group (Zr 500ppm), represented at Snowdonia and Avoca, is interpreted as originally being peralkaline in composition; their high Zr/Nb ratios (>10) are typical of peralkaline rhyolites erupted above subduction zones. The bimodal nature of the associations and the peralkaline character of some rhyolites indicates magma production in a complex tectonic setting, transitional between an active continental margin/island arc and an extensional environment. Associated sulphide mineralization is volcanogenic and probably syn-sedimentary. High-level, rhyolitic magma chambers are thought to have driven convection of the hydrothermal fluids from which the sulphides precipitated.

Volcanological and tectonic control of stratigraphy and structure in the western Deccan traps

Abstract: Many of the world's flood basalt provinces form elevated plateaux at the margins of continents, although in most cases their present large elevation is not the result of mountain building processes. Several explanations have recently been put forward to explain such occurrences of epeirogeny. The Deccan Trap basalt province forms one such elevated plateau, and results are presented here showing how the epeirogenic uplift in this region, combined with crustal subsidence probably associated with the rifting of the Indian continental margin, has affected the structure of the basalt sequence. Trace element analytical data are used for samples from numerous vertical sections through the Deccan Traps lava series along and around the Western Ghats ridge in India. The results reinforce the previously defined stratigraphy of the Mahabaleshwar area, and extend it over a region covering some 36 000 km2, reaching as far south as Belgaum and the Trap/basement contact. These results show that the lava pile is not flat lying, but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0.3 ° over most of the area, although in the south there is evidence of a reversal of this plunge. The fold is interpreted as being the result of two tilting processes: (1) westward tilting near the coast, due to the foundering of the passive continental margin, and (2) epeirogenic uplift along the whole west coast of India producing the observed topography and the peninsula-wide drainage patterns, and also the easterly component of dip. Variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold, although the possibility of some component of depositional dip may also be important. This latter possibility can be modelled using a simple computer program. The results of this modelling show that a migrating linear volcanic edifice fits the observations best.

Higher-order differential equations and higher-order lagrangian mechanics

Abstract: The study of higher-order mechanics, by various geometrical methods, in the framework of the theory of higher-order tangent bundles or jet spaces, has been undertaken by a number of authors recently: for example, Tulczyjew [16, 17], Rodrigues [14, 15] de Leon [8], Krupka and Musilova [11, and references therein]. In this article we wish to complement these studies by approaching the subject from a new point of view, one which we developed for second-order differential equation fields and first-order Lagrangian mechanics in [19]. In particular, our aim is to show that many of the results we obtained there may be extended to the higher-order case.

Receptor-mediated inositol phospholipid hydrolysis in CNS astrocytes

Abstract: Receptor-activated inositol phospholipid hydrolysis in astrocytes was investigated by determining agonist-induced increases in the accumulation of intracellular inositol phosphates. © 1986.

GABA-immunoreactive neurons in the rat cerebellum: a light and electron microscope study.

Abstract: An antibody raised against γ - amino-butyric acid (GABA) coupled to bovine serum albumin with glutaraldehyde (Hodgson et al: J. Histochem. Cytochem. 33:229–239, '85) was used to localise immunocytochemically the presumptive GABAergic neuronal elements in the cerebellar cortex of the adult rat. Employing the unlabelled antibody enzyme method with pre- and postembedding immunocytochemical procedures, the following cellular structures were observed to be GABA-immunopositive in both the light and electron microscopes: the somata, dendrites, and axonal processes (including axon terminals) of stellate, basket, and Golgi neurons. In immunopositive neuronal somata and dendrites, the reaction product was found to be associated with all intracellular organelles and with the postsynaptic densities of synaptic junctions. Specific GABA-like immunoreactivity was also seen around outer mitochondrial membranes, microtubules, and neurofilaments, and coating synaptic vesicles in presynaptic axon terminals. In the pre-embedding procedure with dilutions of the antiserum between 1:1,000 and 1:2,000, the perikarya and dendrites of Purkinje cells were GABA-immunonegative, whereas at an antiserum dilution of 1:500 the somata of Purkinje cells were mildly GABA-immunoreactive. Purkinje cell axon terminals in the infra- and supraganglionic plexuses and in the deep cerebellar nuclei were always strongly immunopositive. Neuroglia were invariably GABA-immunonegative, as were the dendrites, axons (parallel fibres), and somata of granule cells. Mossy fibre and climbing fibre afferents were also immunonegative. The pattern of immunoreactivity obtained with this antiserum directed against the inhibitory neurotransmitter GABA was found to resemble closely the immunocytochemical distribution of GABA and of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) as reported previously in other immunocytochemical investigations (Oertel et al. and Wu et al: Cytochemical Methods in Neuroanatomy. New York: A. R. Liss, '82; Seguela et al: Neuroscience 16:865–874, '85; Mugnaini and Oertel: GABA and Neuropeptides in the CNS. Handbook of Chemical Neuroanatomy. Vol. 4, Part I. Amsterdam: Elsevier, '85):.

The annual reproductive cycle of the Smooth newt (Triturus vulgaris) in England

Abstract: Newts were collected throughout the year from both breeding ponds and terrestrial sites and were weighed, measured and dissected; in males, the testes were examined histologically. Smooth newts show post-nuptial gametogenesis such that, during late summer and autumn they are producing mature gametes for the following year's breeding season. In males, the testes are at their smallest size during the spring, when they consist mostly of immature sperm cysts and evacuated tissue, mature sperm having been evacuated into the vasa deferentia during the newts' migration to water. Evacuated testicular tissue is glandular in function and there is evidence that secretions from this tissue control the development of secondary sexual characters: the dorsal crest, fringes of skin on the toes and the dorsal cloacal gland. In both sexes, fat body and liver weights are lowest in the spring and increase in the autumn. In females, oocytes vary in size, depending on the amount of yolk they contain. Only the larger oocytes are laid in a current breeding season, the smaller ones being retained and yolked in late summer and autumn. In both sexes, measures of fecundity (testis size in males, oocyte number in females) are strongly correlated with body size. The finding that male newts have a finite supply of sperm during the breeding season leads to an interpretation of various aspects of male courtship behaviour. These are adaptations for conserving sperm and allocating it to courtship encounters in a way likely to promote male reproductive success.

Exploiting the 1, 440-fold symmetry of the master two-loop diagram

Abstract: The 1, 440-element symmetry group of the generic two-loop diagram of massless scalar field theory in 4-2ω dimensions is computed, using tetrahedral symmetry and star-triangle duality. Constructing all quadratic and quartic polynomial invariants, we expand the diagram throughO(ω5), where one first encounters a coefficient that does not appear to be expressible in terms of the Riemann zeta function, thereby strengthening previous suspicions that genuinely new calculational comoplexity arises at the level of 6-loop renormalization.

Continuity and Change in the Urban House: Developments in Domestic Space Organisation in Seventeenth-Century London

Abstract: The object of this article is to present the main findings of a study of the functional organisation of the house in postmedieval London. It will also discuss a formal approach to plan analysis that is considered to have wide application in the comparative study of domestic space.

The Jabel Sayid complex, Arabian Shield : geochemical constraints on the origin of peralkaline and related granites

Abstract: The Jabel Sayid Complex comprises two principal rock types which require distinct source regions. An earlier intrusion (572 ± 24 Ma) of biotite-hornblende monzogranite displays selective enrichment of LIL elements and depletion of HREE characterizing a calc-alkaline magma derived from a garnet-bearing source within a hydrated mantle wedge. The younger intrusion (534 ± 40 Ma) is an aegirine-arfvedsonite peralkaline granite which can be derived neither by fractionation of a calc-alkaline magma, nor by closed-system anatexis of a crustal source. This granite is enriched in HFS elements and strongly depleted in Sr, Ba and Eu, and requires the contribution of a fluorine-bearing fluid phase. This volatile phase has resulted in a range of metasomatic rock types including an aplitic rim which carries extreme levels of HFS elements and is a potential economic source of U, and a red granite characterized by widely ranging trace element abundances and strong Eu depletion. The peralkaline granite is typical of siliceous melts derived from an intra-plate tectonic environment, with trace elements strongly controlled by volatiles which are probably mantle-derived. The role of crustal contamination on such granites can neither be proved nor excluded.