Chemical evolution and petrogenetic implications of loparite in the layered,agpaitic Lovozero complex,Kola Peninsula,Russia

Summary Lovozero, the largest of the world’s layered peralkaline intrusions, includes gigantic deposits of Nb + REE-loparite ore. Loparite, (Na,Ce,Ca)₂(Ti,Nb)₂O₆, became a cumulus phase after crystallisation of about 35% of the ‘Differentiated Complex’, and its compositional evolution has been investigated through a 2.35 km section of the intrusion. The composition of the cumulus loparite changes systematically upwards through the intrusion with an increase in Na, Sr, Nb and Th and decrease in REE and Ti. This main trend of loparite evolution records differentiation of the peralkaline magma through crystallisation of 1600 m of the intrusion. The formation of the loparite ores was the result of several factors including the chemical evolution of the highly alkaline magma and mechanical accumulation of loparite at the base of a convecting unit. At later stages of evolution, when concentrations of alkalis and volatiles reached very high levels, loparite reacted with the residual melt to form a variety of minerals including barytolamprophyllite, lomonosovite, steenstrupine-(Ce), vuonnemite, nordite, nenadkevichite, REE, Sr-rich apatite, vitusite-(Ce), mosandrite, monazite-(Ce), cerite and Ba, Si-rich belovite. The absence of loparite ore in the “Eudialyte complex” is likely to be a result of the wide crystallisation field of lamprophyllite, which here became a cumulus phase. Received November 6, 2000; revised version accepted January 18, 2001     

Nature and culture in social science: the demarcation of domains of being in eighteenth century and modern discourses

Modern social science is concerned with policing the ‘boundary’ between nature and culture, with limiting and excluding phenomena which threaten to challenge its account of the social determination of the attributes of human beings. The paper argues that this boundary defence is an unusually touchy and difficult matter because social science has inherited an Enlightenment conception of man as ‘unique’. Human culture is regarded as different in quality from any possible form of animal association or attainment. At the same time as supporting this ontology it supposes the ‘boundary’ is in some sense a matter of empirical science, capable of specification by reference to evidence. We try to show the confusions these two contradictory circumstances produce by considering two debates: those concerning the possibility of ‘feral’ children and those concerning the uniqueness of language to human beings. It is demonstrated that the modern debates develop theories, issues and lines of dispute which appeared in the eighteenth century.     

The analcime-phyric phonolites (blairmorites) and associated analcime kenytes of the Lupata Gorge,Mocambique

The petrology and mineralogy of three lavas from the Lupata Gorge, Mocambique, containing primary euhedral analcime phenocrysts, up to 1.5 cm in diameter, as well as potassium feldspar and nepheline phenocrysts, are described. Electron microprobe analyses of these phases and a whole rock analysis of the blairmorite are given. Reference to published and unpublished experimental work indicates that these rocks must have been generated at water pressures between about 5 and 13 kbars, implying depths of origin of between 20 and 50 km. Very rapid transport to the surface and quenching is implied. It is suggested that these indications of the considerable depth of origin of these rocks, taken together with the absence of associated intermediate and basic rocks, lends credence to the hypothesis of D. K. Bailey that the voluminous associations of salic igneous rocks found in parts of the African continent, unaccompanied by associated basic rocks, are explicable in terms of partial melting, under high water pressures, of the lower part of the crust.     

A basalt-trachyte-phonolite series from Ua Pu,Marquesas Islands,Pacific Ocean

The paper describes a suite of volcanic and intrusive rocks from Ua Pu, one of the Marquesas Islands, situated in the central Pacific Ocean. The rocks comprise alkali olivine basalts, hawaiites, mugearites, trachytes, and phonolites. Their petrographic characters are briefly described and 24 new chemical analyses presented. The rocks fall into a sodic and a potassic series, since some rocks are richer in K₂O than Na₂O, whilst the phonolites have exceptionally high total alkali contents.The differentiation of the series is discussed and special attention is paid to the phonolites in which icositetrahedral pseudomorphs occur. It is concluded that these pseudomorphs are probably after analcime rather than leucite.     

An investigation of rare-earth mobility: Fenitized quartzites,Borralan complex,N.W. Scotland

Examples of fenitization of pure quartzites provide valuable insight into the relative mobility of elements. This investigation of fenites from the Borralan complex shows that rare-earth elements are mobile and added during fenitization of quartzite. The resulting normalized patterns are distinctive in their enrichment of the light rare earths and steep drops in the interval Nd-Eu. In terms of rare-earth geochemistry, no difference can be found between the sodic and the potassic trends of fenitization at Borralan. Concentrations of mobile elements define straight-line plots through the origin, heretofore considered a criterion indicative of a fractional crystallization process.Present address: Department of Geological Sciences, McGill University, 3450 University Street, Montreal, Que. H3A 2A7, Canada     

Extrusive carbonatites: A brief review

49 known extrusive carbonatite occurrences are listed with brief details of their tectonic setting, structure, lithologies, associated silicate rocks, chemistry and presence or absence of included mantle materials. Half the occurrences appear to be related to tephra cones, tuff rings, diatremes and maars and the rest occur within strato-volcanoes. Pyroclastic carbonatitic rocks are present at all the localities, with carbonatite lava flows occurring at only 14 of them. The pyroclastic rocks, which include fallout tephra and deposits from pyroclastic surges and flows and products of phreatomagmatic eruptions, vary from rocks composed principally of carbonate to varieties with as little as 20% igneous carbonate. The most abundant silicate rocks associated with extrusive carbonatites are melilite-bearing rocks, nephelinite and/or ijolite, and phonolite and/or nepheline syenite; seven occurrences have no associated silicate rocks. 16 occurrences, most of them associated with small extrusive centres, contain mantle xenoliths or megacrysts, details of which are tabulated, with spinel lherzolite the most abundant rock type, but amphibole, phlogopite and garnet are also recorded. The lack of such materials in intrusive carbonatites may reflect their less energetic environment of emplacement. It is proposed that carbonatites are essentially of two types: (a) those rising energetically and rapidly from the mantle, which form small explosion craters, ash or tuff cones, or diatremes, have only low-volume associated silicate rocks, and entrain mantle debris, and (b) those which occur in strato-volcanoes, are associated with large volumes of silicate rocks and follow a more complex genesis, probably involving ponding and differentiation (separation from carbonate-bearing silicate magma) at higher levels in the mantle and/or crust. Most of the classic intrusive carbonatite complexes probably fall into the second category.     

Applicability and methodology of determining sustainable yield in groundwater systems

There is currently a need for a review of the definition and methodology of determining sustainable yield. The reasons are: (1) current definitions and concepts are ambiguous and non-physically based so cannot be used for quantitative application, (2) there is a need to eliminate varying interpretations and misinterpretations and provide a sound basis for application, (3) the notion that all groundwater systems either are or can be made to be sustainable is invalid, (4) often there are an excessive number of factors bound up in the definition that are not easily quantifiable, (5) there is often confusion between production facility optimal yield and basin sustainable yield, (6) in many semi-arid and arid environments groundwater systems cannot be sensibly developed using a sustained yield policy particularly where ecological constraints are applied. Derivation of sustainable yield using conservation of mass principles leads to expressions for basin sustainable, partial (non-sustainable) mining and total (non-sustainable) mining yields that can be readily determined using numerical modelling methods and selected on the basis of applied constraints. For some cases there has to be recognition that the groundwater resource is not renewable and its use cannot therefore be sustainable. In these cases, its destiny should be the best equitable use.