Graphical estimations of magma densities and compositional expansion coefficients

Assuming that the partial molar volume of each chemical component in a magma is constant, the magma density, _m , is expressed as 1/ _m =C _i / _fi , whereC _i is the weight fraction, and _fi is the fractionation density of thei ^th component. Using this linear relationship between 1/ and weight fraction, the density change due to addition or subtraction of any component can be graphically estimated on 1/ vs oxide wt% diagrams. The compositional expansion coefficient of thei ^th component, _fi , is expressed as _i = _m / _fi –1. The compositional expansion coefficient of H₂O has a much larger absolute value than those of any other oxide or mineral components, showing that addition of a small amount of H₂O can significantly decrease magma density. These simple expressions facilitate the estimation of magma densities during fractionation.     

The system: Two alkali feldspars-KCl-NaCl-H2O at moderate to high temperatures and low pressures

Because of frequent discrepancies between the available experimental data and the measured composition of alkali chloride aqueous solutions coexisting with two alkali feldspars in high temperatures-low pressures natural systems, a systematic investigation of the system KAlSi₃O₈-NaAlSi₃O₈-KCl-NaCl-H₂O has been undertaken.Experiments have been carried out at temperatures from 300 °C to 660 °C, pressures from 0.2 to 2 kbar and total chloride concentrations ranging from 0.05 to 14 moles/kg H₂O.No effect of pressure on the feldspars solvus could be detected. Smoothing the experimental data on the basis of the regular assymetric solid solution model yields a critical temperature of 661°C and a critical composition of Or_0.36Ab_0.64.The equilibrium constant C = m _KCl/m _NaCl does not depend on total chloride molality, as long as the aqueous solution is homogeneous. But, in the miscibility gap (liquid+vapour) of the fluid, C is always lower in the vapour than in the liquid. The higher the temperature and the lower the pressure, the more striking this effect. For instance, at 500 ° C C _vaqour/C _liquid = 1 above 1 kb, 0.9 at 600 bars, 0.8 at 500 bars, 0.7 at 400–450 bars.The effect of pressure can be neglected in homogeneous fluids and in the liquid phase of unmixed fluids, but it is very important in the vapour phase (dilute solutions at low pressure).The selected values of C _max are (±0.01) 300 ° C0.083; 400 ° C0.139; 500 ° C0.200; 600 ° C0.264; 650 ° C0.298Such a behaviour of the fluid at low pressures explains the abnormally low values of m _KCl/m _NaCl measured in many natural hydrothermal systems. A new mechanism of alkali metasomatism (especially potassic alterations) is also proposed, taking into account the unmixing of alkali chloride aqueous solutions. This model seems particularly interesting in late magmatic hydrothermal processes, such as those occuring in porphyry type deposits.     

Comparison between two types of multifractal modeling

The interrelationships between two previously developed multifractal models are discussed. These are the Evertsz-Mandelbrot model developed on the basis of the multifractal spectrum f(), and the Schertzer-Lovejoy model based on the codimension function C() where and represent Hölder exponent and field order, respectively. It is shown how these two models are interrelated: they are identical for values of within the range D–(0)D–_min. where D is the Euclidean dimension. For D–_maxD–(0), however, f() remains a continuous function of whereas C() assumes constant value. In this respect, the fractal spectrum f() can provide more information about the multifractal measure than the codimension function C(). The properties of the two models are illustrated by application to the binomial multiplicative cascade model.     

Formalities too — On language,maps, and human geography

Current developments within the human sciences in general and social geography in particular have challenged the paradigm of representation that has prevailed here as elsewhere for the longest time since the Enlightenment. The paper at hand seeks to explore some of the wider ramifications of this so-called postmodern challenge for those forms of expression that geographers have become accustomed to. Primarily the map, unique in its importance for the pursuit of geographical knowledge, will be analyzed from a decidedly abstract point of view.     

Hydrothermale Lösungen

Zusammenfassung Das hydrothermale Auflösungsverhalten der vorwiegend als Gangarten auf-tretenden Mineralphasen Fluorit (CaF₂), Baryt (BaSO₄), Cölestin (SrSO₄) und Anglesit (PbSO₄) läßt sich übersichtlich in einem Temperatur-Löslichkeitsdiagramm darstellen und mit dem bekannten, qualitativ ähnlichen System SiO₂-H₂O vergleichen.Gegenüber dem molekulardispers gelösten SiO₂ ergeben sich aber für die in Ionen dissoziierten Lösungen der schwerlöslichen Sulfate und des Fluorits beträchtliche Verschiebungen der Sättigungsgleichgewichte, insbesondere bei Anwesenheit von Elektrolyten als Lösungsgenossen.Diese Beeinflussung, die für die genetischen Verhältnisse der Minerallagerstätten von entscheidender Bedeutung ist, wird für 0,1–2,0 normale NaCl-Lösungen im NaCl-Konzentrations-Löslichkeits-Diagramm der Minerale Fluorit, Baryt, Cölestin und Anglesit isotherm bis zum Siedepunkt der wäßrigen Mischphasen untersucht.Ferner wird das Löslichkeitsverhalten in den ternären Systemen BaSO₄-NaCl-H₂O und SrSO₄-NaCl-H₂O für Baryt und Cölestin gegen 2,0n NaCl-Lösungen entlang der Grenzkurve des Dreiphasengebietes und für die Isochoren 0,326 bis 0,6 bis 600° C und 2000 Bar dargestellt und mit den entsprechenden Verhältnissen der reinen wäßrigen Systeme verglichen.Ein abweichendes inkongruentes Auflösungsverhalten von Alumosilikaten mit Schichtgitterstruktur läßt sich am Beispiel des Muskovits durch die experimentelle Bestimmung der nichtstöchiometrischen Molekularverhältnisse SiO₂/K₂O und SiO₂/Al₂O₃ in den gesättigten Lösungen für den hydrothermalen Existenzbereich des Muskovits nachweisen.

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The behaviour of solubility for some minerals, which were for the most part found as vein minerals, was determined experimentally and is represented by summarizing diagrams.In the temperature-solubility diagram the hydrothermal solubility of fluorite, barite, celestine and anglesite is compared to the solubility of quartz and muskovite for the boundary curve of the three-phase region and for some isochores. As opposed to SiO₂, which is molecularly dispersed in solution, the ionic solutions of the systems CaF₂-H₂O, BaSO₄-H₂O, SrSO₄-H₂O and PbSO₄-H₂O show considerable displacement of the saturation equilibrium when other components are present in the solution.This influence on the solubility, significant for the genetic relations of mineral deposits, was quantitatively analyzed for 0.1–0.2 n-NaCl solutions. The results are isothermally shown in the NaCl-concentration solubility diagram within the boundaries of room temperature and the boiling point of the aqueous mixed phases.In the tenary systems BaSO₄-NaCl-H₂O and SrSO₄-NaCl-H₂O, the hydro-thermal solubility of barite and celestine in 2.0 n-NaCl solutions is also shown for the range of the boundary curve of the three-phase region and for the isochores 0.326–0.6 up to a temperature of 600° C and a pressure of 2000 bar. These solubilities are then compared with the diagrams of solubility for pure aqueous solutions.The irregular and incongruent behaviour of the solubility of aluminium-silicates of a layered-lattic structure is demonstrated for the system KAl₂(OH)₂-AlSi₂O₁₀-H₂O in the presence of muscovite by experimental determination of the non-stoechiometric molecular proportions of SiO₂K₂O and SiO₂ Al₂O₃. Such determination was conducted in saturated solutions for the hydrothermal range of the existence of muscovite.The geological importance of the knowledge of hydrothermal data of solubility and their application to the process of the hydrothermalmagmatic series and hydrothermalmetamorphosis is discussed.

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Résumé Le comportement de dissolution expérimentalement déterminé de certains minéraux trouvés surtout en filons est exposé en le résumant par diagrammes.La solubilité hydrothermique de fluorine, barytine, célestine et anglésite est comparée pour la courbe limitante (de la région triphasée) et pour les isochores 0,326–0,6 g.cm³ du diagramme température-solubilité avec le comportement de dissolution du quartz et de la muscovite. Les solutions ioniques des systèmes CaF₂H₂O, BaSO₄-H₂O, SrSO₄-H₂O et PbSO₄-H₂O montrent, comparées au SiO₂ dissous en dispersion moléculaire, de différences importantes d'équilibres de saturation en présence d'associés de solution.Cette influence sur la solubilité qui est d'une importance décisive pour les conditions génétiques des gisements de minéraux, a été examinée quantitativement pour les solutions 0,1–0,2—normales de NaCl. La présentation s'est faite isothermiquement dans le diagramme de concentration-solubilité de NaCl entre la température de chambre et le point d'ébullition des phases mixtes aqueuses.Dans les systèmes ternaires BaSO-NaCl-H₂O et SrSO₄-NaCl-H₂O la solubilité hydrothermique de barytine et de célestine en des solutions 2,0-normales de NaCl est présentée également pour l'espace des courbes limitantes de la région triphase et pour les isochores 0,326–0,6 jusqu'à 600° C et 2000 Bar. Elle est comparée avec les courbes de solubilité de systèmes purement aqueux. Le comportement de dissolution divergeant incongruent des silicates d'alumine à structure stratifiée en treillis est démontré pour le systême KAl₂(OH)₂-AlSi₃O₁₀-H₂O par exemple de la muscovite en déterminant expérimentalement les proportions moléculaires non-stochiométriques SiO₂ K₂O et SiO₂Al₂O₃ dans les solutions saturées pour la domaine d'existence hydrothermique de la muscovite.Importance géologique de la connaissance des dates de solubilité hydrothermique et leur application sur les événements des conséquences hydrothermiques-magmatiques et sur les événements de la métamorphose hydrothermique sont discutées.

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y 600° 2000 . (CaF₂), ( SO₄), . (SrSO₄) (PbSO₄) - Sio₂-₂.

     

Alkaline rocks and carbonatites of Amba Dongar and adjacent areas,Deccan Alkaline Province,Gujarat, India. 2. Complexly zoned clinopyroxene phenocrysts

Summary Clinopyroxene phenocrysts in six samples, representing the compositional range in the alkaline rocks of the region, range overall from aluminian titanian diopside (mg = Mg/[Mg + Fe _t ] = 92) to aegirine (mg = 17), but Ca-pyroxenes are dominant (90% of 851 analyses), Ca-Na pyroxenes minor ( 10%) and Na-pyroxenes rare ( 1%). Pyroxenes in associated subalkaline rocks (dolerites and basalts) are lower-Ca augites of distinct trend. Al and Ti correlate positively in the alkaline rock pyroxenes, but negatively with Si, mirroring decreasing CaTiAl₂O₆ and CaSiAl₂O₆ components in more felsic host-rocks. Although the most evolved pyroxenes in each host-rock show increasingna (Na/[Na + Ca]) and Zr and decreasingmg as host-rock mg decreases, the most primitive pyroxenes in each host-rock do not change, implying they are not at equilibrium. Over 40 paired logitudinal and lateral traverses across 21 phenocrysts reveal very complex zoning, in which up to five growth zones can be recognized in one crystal, separated by either sharp contacts or gradual transitions. These individual zones may show one of seven zoning trends:normal (na asmg moving outwards towards the rim),reverse (na asmg ),inverse (na asmg ),converse (na asmg ),unzoned (no change),symmetric (na andmg display complementary and trends), oroscillatory (superimposed on normal, reverse or unzoned). Ten distinct crystal types can also be recognized, showing particular sequences of zoning trends: for example, Type 1 shows a green, relatively sodic core surrounded by a more primitive rim or overgrowth, and has similar longitudinal and lateral zoning; whereas Type 6 shows extremely erratic variations which differ longitudinally and laterally. Up to four of these types were found in one host-rock, with little pattern in their distribution between different host-rocks. These pyroxenes are believed to record an intricate history of stop-start differentiation, complicated by magma-mixing, entry or disappearance of coprecipitating phases, and inheritance of high-pressure precipitates. Apparently random superimposed variations of Al, Ti and Si within some individual growth zones most probably reflect kinetic (disequilibrium) effects, due to rapid growth and/or supercooling.

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Alkaligesteine und Karbonatite von Amba Dongar und Umgebung Deccan Alkali-Provinz, Gujarat, Indien. 2. Komplex zonierte Klinopyroxenkristalle

Zusammenfassung Klinopyroxenkristalle in sechs Proben, die das ganze Spektrum der Zusammensetzung der Alkaligesteine des Gebietes repräsentieren, schwanken von Aluminium-Titandiopsid (mg = Mg/[Mg + Fe _t ] = 92) bis Aegirin (mg = 17), aber C-Pyroxene dominieren (90% von 851 Analysen). Ca-Na-Pyroxene sind Nebengemengteile (10%) und Na-Pyroxene sind selten ( 1%). Pyroxene in assoziierten subalkalischen Gesteinen (Dolerite und Basalte) sind Ca-arme Augite eines eigenständigen Trendes. Al und Ti korrelieren positiv in den Pyroxenen der Alkaligesteine, aber negativ mit Si, und dies spiegelt abnehmende CaTiAl₂O₆ und CaSiAl₂O₆ Komponenten in den mehr felsischen Wirtsgesteinen wider. Obwohl Pyroxene in jedem Wirtsgestein zunehmende na-Werte (Na/[Na + Ca]) und Zr-Gehalte und mit demmg des Wirtsgesteines auch abnehmendemg-Werte zeigen, lassen die primitivsten Pyroxene in jedem Wirtsgestein keine Änderung erkennen. Dies weist darauf hin, daß sie nicht im Gleichgewicht sind. Über vierzig paarweise angelegte Längs- und Quertraversen über 21 Kristalle zeigen sehr komplexen Zonarbau, in dem bis zu fünf Wachstumszonen in einem Kristall erkannt werden können, die entweder von scharfen Kontakten oder von graduellen Übergangszonen getrennt werden. Diese individuellen Zonen können einen der folgenden sieben Trends erkennen lassen: Normal (na ;mg ; von innen gegen den Rand zu), reverse (na ,mg ), invers (na undmg ), konvers (na ,mg ), unzoniert (keine Änderung), symmetrisch (na undmg zeigen komplementäre und Trends), oder oszillierend (überlagert den normalen, reversen oder unzonierten Trend). Weiters können zehn definierte Kristalltypen erkannt werden, die besondere Abfolgen von Trends der Zonierung erkennen lassen. Zum Beispiel zeigt Typ 1 einen grünen, relativ Na-reichen Kern, umgeben von einem mehr primitiven Rand oder Überwachsungen, wobei die Zonierung in Längs- und Querrichtung ähnlich ist. Demgegenüber zeigt Typ 6 außerordentlich unregelmäßige Zonierungen, die in Längs- und Querschnitten verschieden sind. Bis zu vier dieser Typen wurden in einem Wirtsgestein nachgewiesen, und sie ließen keine deutlichen Verteilungsmuster zwischen verschiedenen Wirtsgesteinen erkennen. Es wird angenommen, daß diese Pyroxene eine komplexe geschichte von stop-start Differentiation wiedergeben, die durch Magmamischung, durch die Zufuhr oder das Verschwinden von gleichzeitig ausfallenden Phasen und durch die Übernahme von Hochdruck-Bildungen weiter kompliziert wird. Unregelmäßig überlagerte Variationen von Al, Ti und Si innerhalb einzelner Wachstumszonen reflektieren sehr wahrscheinlich kinetische (Ungleichgewicht) Effekte, die auf sehr rasches Wachstum und/oder Überkühlung zurückgehen.

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With 11 Figures     

Mean and turbulent velocity measurements of supersonic mixing layers

The behavior of supersonic mixing layers under three conditions has been examined by schlieren photography and laser Doppler velocimetry. In the schlieren photographs, some largescale, repetitive patterns were observed within the mixing layer; however, these structures do not appear to dominate the mixing layer character under the present flow conditions. It was found that higher levels of secondary freestream turbulence did not increase the peak turbulence intensity observed within the mixing layer, but slightly increased the growth rate. Higher levels of freestream turbulence also reduced the axial distance required for development of the mean velocity. At higher convective Mach numbers, the mixing layer growth rate was found to be smaller than that of an incompressible mixing layer at the same velocity and freestream density ratio. The increase in convective Mach number also caused a decrease in the turbulence intensity ( _u /U).List of Symbols a speed of sound - b total mixing layer thickness betweenU ₁ – 0.1U andU ₂ + 0.1U - f normalized third moment ofu-velocity,f u ³/(U)³ - g normalized triple product ofu ² v,g u ² v/(U)³ - h normalized triple product ofu v ², h uv' ²/(U)³ - l _u axial distance for similarity in the mean velocity - l _u axial distance for similarity in the turbulence intensity - M Mach number - M _c convective Mach number (for ₁=₂),M _c (U ₁–U ₂)/(a ₁+a ₂) - P static pressure - r freestream velocity ratio,rU ₂/U ₁ - Re unit Reynolds number,Re U/ - s freestream density ratio,s ₂/ ₁ - T _t total temperature - u instantaneous streamwise velocity - u deviation ofu-velocity,u u–U - U local mean streamwise velocity - U ₁ primary freestream velocity - U ₂ secondary freestream velocity - U average of freestream velocities, ¯U (U ₁ +U ₂)/2 - U freestream velocity difference,U U ₁ –U ₂ - v instantaneous transverse velocity - v deviation ofv-velocity,v v – V - V local mean transverse velocity - x streamwise coordinate - y transverse coordinate - y ₀ transverse location of the mixing layer centerline - ensemble average - ratio of specific heats - boundary layer thickness (y-location at 99.5% of free-stream velocity) - similarity coordinate, (y –y ₀)/b - compressible boundary layer momentum thickness - viscosity - density - standard deviation - dimensionless velocity, (U –U ₂)/U - 1 primary stream - 2 secondary stream A version of this paper was presented at the 11th Symposium on Turbulence, October 17–19, 1988, University of Missouri-Rolla     

Spinels as petrogenetic indicators: Activity-composition relations at low pressures

Provisional activity-composition relations have been developed for spinels in the system FeO-MgO-Fe₂O₃-Al₂O₃-Cr₂O₃-TiO₂. These relations are based on a Temkin type model for the configurational entropy combined with a third-degree Taylor's series expansion to describe the excess Gibbs energy of mixing that is the result of describing spinels in terms of a set of fictive ordered and inverse spinel components. The coefficients of this expansion have been identified as (1) reciprocal Mg-Fe exchange terms, (2) binary asymmetric Margules parameters, and (3) Margules and Bragg-Williams type terms which make explicit provision for mixing of Fe and Mg on two sites in ulvospinel. Provisional values have been assigned to these terms for the temperature range 900–1,250°C based on inferred and experimentally determined spinel miscibility gaps, Fe-Mg olivine-spinel exchange data reported in the literature, and 40 experimental determinations of Fe-Mg partitioning between olivines and spinels in basanitic to uganditic silicate liquids between 1,092 and 1,300°C ( QFM).     

The high-pressure assemblages at Milos,Greece

Metamorphic rocks at Milos are known in small outcrops beneath the volcanic formations, as xenoliths in the Traphores volcanic breccia and as pebbles in the Paleochora Quaternary deposits. These rocks seem to belong to three different metamorphic units which probably have intricate relationships in the basement: — the eclogites unit shows garnetjadeite or garnet-omphacite primary associations, with apparently late crystallization of lawsonite phenoblasts an recrystallization features at relatively low temperatures; — the glaucophane schist unit exhibits Jadeite+quartz or glaucophane+lawsonite primary mineralogy; — the greenschist facies unit shows low-pressure main assemblages, most generally developed after high-pressure events. The two former units involve tholeiitic meta-igneous rocks, having been spilitized before metamorphism; they generally suffered more or less advanced recrystallization features in the low-pressure field of the greenschist facies. The third unit shows only meta-sedimentary rocks, with the sole exception of one single meta-doleritic pebble having calk-alkaline affinities.Petrological and mineralogical studies, based upon 15 bulk-rock compositions and 178 probe-analysed data points, lead to suspect at least 2, perhaps 3, different metamorphic events rather than one single metamorphic evolution, to account for the 3 U distinguished. From the observation of the mineralogical assemblages and their evolution, the former events (stages 1 and 2) could be related to rapid subduction of ocean-floor or back-arc basalts, whereas, during the latter event (stage 3), the rocks experienced crystallization conditions involving both decreasing pressures and increasing temperatures.     

Kristallchemie natürlicher Telluride I: Verfeinerung der Kristallstruktur des Sylvanits,AuAgTe4

Zusammenfassung Mikrosondenanalysen und die Verfeinerung der Kristallstruktur zeigen, daß Sylvanit, AuAgTe₄, aus Baia de Arie (=Offenbánya), Rumänien, eine stöchiometrische Zusammensetzung und eine geordnete Kristallstruktur besitzt (a=8,95(1) Å,b=4,478(5) Å,c=14,62(2) Å; =145,35(5)°;Z=2; RaumgruppeP2/c–C _2h ⁴ ). Das Au-Atom ist von sechs Te-Atomen in einer für die Oxidationszahl III charakteristischen [4+2]-Koordination umgeben. Um das Ag-Atom (Oxidationszahl I) sind ebenfalls sechs Te-Atome, jedoch in einer [2+2+2]-Koordination, angeordnet. Über gemeinsame Kanten bauen AuTe₆- und AgTe₆-Polyeder Schichten parallel (100) auf. Diese Schichten werden über Te₂-Hanteln (Te–Te=2,82 Å) zu einem Gerüst verknüpft.

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Crystal chemistry of natural tellurides. I: Refinement of the crystal structure of sylvanite, AuAgTe₄

Summary Electron microprobe analyses and the refinement of the crystal structure indicate, that sylvanite, AuAgTe₄, from Baia de Arie (=Offenbánya), Romania, has a stoichiometric composition and an ordered crystal structure (a=8.95(1) Å,b=4.478(5) Å,c=14.62(2) Å; =145.35(5)°;Z=2; space groupP2/c–C _2h ⁴ ). The Au atom is surrounded by six Te atoms in a [4+2] coordination as characteristic for oxidation state III. Around the Ag atom (oxidation state I) are also six Te atoms, but arranged in a [2+2+2] coordination. Via common edges the AuTe₆ and AgTe₆ polyhedra build up sheets parallel to (100). These sheets are combined to a network of Te₂ dumbbells (Te–Te=2.82 Å).

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Mit 2 Abbildungen     

Laterites of Sri Lanka — A reconnaissance study

Laterites occur extensively in the lowlands of Sri Lanka whereas these are observed as localized outcrops in the uplands and the highlands. In lateritis weathering profiles, Al-rich zones are found between and beneath harder Fe-rich layers. The processes of lateritisation and bauxitisation have produced residual products enriched in both Fe₂O₃ and Al₂O₃. In the lowlands and uplands the lateritisation processes have prevailed and the bauxitisation trend is more pronounced in the highlands.

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Résumé Les gisements latéritiques s' observent largement dans les lowlands du Sri Lanka. Mais dans les uplands et highlands les affleurements latéritiques sont rares. Aux profils d'altération les zones riches en Al se trouvent entre ou sous les zones plus dures mais riches en Fe. Les deux processus de latéritisation et bauxitisation ont donné lieu aux produits résiduels riches en Fe₂O₃ ainsi qu'en Al₂O₃. Il a été observé que le processus de latéritisation se produit plus souvent dans les lowlands et uplands tandis que la bauxitisation est plus repandue aux highlands.

     

Magmatic and hydrothermal R.E.E. fractionation in the Xihuashan granites (SE China)

The Xihuashan stock (South Jiangxi, China) is composed of cogenetic granitic units (granites Xe, a, c, d and b) and emplaced during the Yanshanian orogeny (153±0.2 Ma). They are two feldspars, Fe-rich biotite±garnet and slightly peraluminous granites. Primary accessory minerals are apatite 1, monazite, zircon, uranothorite±xenotime in granites Xe and a, zircon, uranothorite, uraninite, betafite, xenotime 1; hydrothermal minerals are monazite altered into parisite and apatite 2, Y-rich parisite, yttroparisite, Y-rich fluorite and xenotime 2 in granites c and b. Petrographic observations, major element, REE, Y and Rb–Sr isotropic data point to a magmatic suite (granites Xe and a granites c and d granite b) distinct from hydrothermal Na-or K-alteration of b. From granite Xe to granite b, LREE, Eu, Th and Zr content are strongly depleted, while HREE, Y and U content increase. During K-alteration of b, these variations are of minor importance. Major and accessory mineral evidences, geochemical and fluid inclusion results indicate two successive alteration fluids interacting with b, (1) a late-magmatic F^– and CO₂–rich fluid and (2) a post-magmatic, aqueous and slightly saline fluid. The depletion of LREE and Th content and the increase in HREE, Y and U content correspond, in the magmatic suite to the early fractionation of monazite in the granites where there is no hydrothermal alteration (granites Xe and e) and to the hydrothermal alteration of monazite into parisite and secondary apatite, intense new formation of yttroparisite, Y enrichment and U loss in the uranothorite and late crystallization of uraninite in the granites c and b. Moreover, simulated crystallization of monazite and temperature of monazite saturation show early fractionation of monazite from the magma in the less evolved granites (Xe and e) and prevailing hydrothermal leaching of monazite in the most evolved granites (c-d and b) related to a late-magmetic event. The slight variations of REE, Y, Th and U content in the K-altered granites compared to granite b emphazes the distinct chemical nature of the successive hydrothermal fluids. Rb–Sr and Sm–Nd isotopic results point to a 30 Ma period of time between the late-magmatic and the post-magmatic fluid circulation.     

The metasomatic development of zoned ultrabasic bodies in Unst,Shetland

Read (1934b) described the mineralogy and regional setting of spectacularly zoned ultrabasic bodies occurring in Unst, Shetland. Chemical and phase compositional data are presented here for a selection of samples taken from each of the several monomineralic zones.The phase sequence and elemental distribution are discussed in some detail since both are complicated. It is shown that virtually all distributional features may be explained on the basis of a diffusion model: transport most probably having occurred via aqueous solutions in pore space.The present configurations represent frozen reaction intermediates. Controls upon the nature and extent of reaction are analysed. Certain features may be explained on the basis of local equilibrium thermodynamics. These arguments, however, are inadequate. Fairly simple kinetic considerations lead to a much more satisfactory analysis.Some of the problems associated with concepts of element mobility are discussed briefly.     

The potassic feldspar in metamorphic rocks from the western Hohe Tauern area,eastern Alps

Zusammenfassung Es wurden Kalifeldspäte aus Orthogneisen, Paragneisen und Glimmerschiefern des westlichen Tauemfensters (Hohe Tauern, Tirol) mit optischen und röntgenographischen Methoden im Hinblick auf ihren Strukturzustand untersucht.Es zeigte sich, daß in den Randbereichen des Tauemfensters in Gesteinen der Grünschieferfazies weitgehend geordneter Mikroklin mit einem optischen Achsenwinkel 2 V_x 80°, Auslöschungswinkel Z (010)=15–20°, Doppelbrechung n_z-n_x= 0,0065, Triklinität=0,90-–0,95, ca. 0,88 Al auf T₁O-Position und einem Ab-Gehalt von ca. 5 Gew.% auftritt. Dagegen wurden in Gesteinen der schwachtemperierten Amphibolitfazies des zentralen Bereichs Orthoklase bis intermediäre Mikrokline mit stark schwankenden optischen Eigenschaften, mit Triklinitäten zwischen 0 und 0,7, 0,8 bis 0,9 Al in T₁-Positionen, 0,45–0,8 Al auf T₁O und Ab-Gehalten von ca. 10 Gew.% festgestellt. Die Kalifeldspatkristalle zeigen ungleichmäßige Auslöschung mit Winkeln von Z (010) zwischen 0 und 15°, 2 V_x zwischen 50 und 75° und n_z-n_x=0,005 bis 0,006. Teilweise ist Zonarbau mit geringerer Triklinität am Kornrande erkennbar. Diese undulös auslöschenden Kalifeldspäte enthalten einzelne schmale Lamellen von maximal triklinem Mikroklin mit Z (010)=15–20° und n_z-n_x= 0,006–0,007.Die Grenze zwischen dem Verbreitungsgebiet von maximalem Mikroklin einerseits und Orthoklas bis intermediärem Mikroklin andererseits verläuft in den westlichen Hohen Tauern ungefähr konform mit der Albit-Oligoklas-Grenze (Morteani &Raase, 1974) und mit der aus Sauerstoff-Isotopen-Untersuchungen bestimmten 500° C-Isotherme (Hoernes &Friedrichsen, 1974).

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The potassic feldspar in orthogneisses, paragneisses, and mica schists from the western Tauernfenster (Hohe Tauern, Tyrol) were studied by optical and X-ray methods with regard to their structural state and in relation to grade of metamorphism.In the peripheral region of the Tauernfenster in greenschist-facies rocks highly triclinic microcline occurs with an optic angle 2 V_x of about 80°, extinction angle Z (010) =15–20°, birefringence n_z-n_x=0.0065, triclinicity=0.90–0.95, approx. 0.88 Al in T₁O-site, and an Ab-content of about 5 wt.%. In the central area with rocks of the low-grade amphibolite facies, on the other hand, orthoclase to intermediate microcline with highly variable optical properties, triclinicities in the range of 0–0.7, 0.8–0.9 Al in T₁-sites, 0.45–0.8 Al in T₁O-site, and an Ab-content of about 10 wt.% was recognized. The K-feldspar grains have nonuniform extinction Z (010) scattering in the range of 0–15°, 2 V_x in the range of 50–75°, and n_z-n_x= 0.005–0.006. Sometimes a zonal structure with lower triclinicity exists at the rim. These undulatory K-feldspar grains usually contain small lamellae of highly triclinic microcline with Z (010) =15–20° and n_z-n_x=0.006–0.007.From the occurrence of maximum microcline and of orthoclase to intermediate microcline in the Hohe Tauern area an isograd was defined that is approximately conformable with the albite-oligoclase isograd (Morteani &Raase, 1974) and with the 500° C isotherm based on oxygen isotope analyses (Hoernes &Friedrïchsen, 1974).

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Résumé Les feldspaths potassiques d'orthogneiss, de paragneiss et de micaschistes de la Fenêtre des Tauern occidental (Hohe Tauern, Tirol) ont été étudiés du point de vue de leur état structural.Dans les roches du faciès schistes verts de la région périphérique de la Fenêtre des Tauern les microclines sont caractérisés par un angle des axes optiques 2 V_p =80°, un angle d'extinction n_g (010)=15–20°, une biréfringence n_g-n_p=0,0065, une triclinicité= 0,90–0,95, 0,88 Al dans le site T₁O et par une teneur en albite d'environ 5%. Au contraire, dans les roches du faciès amphibolite à faible degré de la région centrale, ont été observées des orthoses allant à des microclines intermédiaires avec des propriétés optiques très variables, un degré de triclinicité de 0 à 0,7, 0,8–0,9 Al dans les sites T₁, 0,45–0,8 Al dans T₁O et avec une teneur en albite d'environ 10%.Les cristaux de feldspath montrent une extinction irrégulière avec des angles Z (010) variable de 0 à 15°, 2 V_p de 50 à 75° et n_g-n_p=0,005–0,006.On peut voir quelquefois une structure zonée avec une triclinicité moindre au bord des cristaux. Ces feldspaths potassiques contiennent de minces lamelles de microcline à triclinicité maximum, avec n_g (010)=15–20° et n_g-n_p 0,006–0,007.La limite entre les régions à microcline maximum d'une part, et à orthose ou microcline intermédiaire d'autre part, suit, dans les Hohe Tauern, sensiblement l'isograde albite-oligoclase (Morteani &Raase, 1974) et, l'isotherme de 500° C telle qu'elle fut determinée les isotopes de l'oxygène (Hoernes &Friedrichsen, 1974).

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, ( , ) ., 2 V_x80°, Z (010)=15–20°, n_z–n_x=0,0065, =0,90–0,95, 0,88 l T₁O Ab 5 .-%. , 0 0,7, 0,8-0,9 1 T₁ l 10 .-%. Z V (010) 0 15°, 2 V_x 50 75° n_z–n_x=0,005–0,006. . Z V (010) =15-20° n_z–n_x=0,006–0,007. , Morteani & Raase (1974) 500° , Hoernes & Friedrichsen (1974).

     

Natural boehmite single crystals from Ceylon

Single crystals of boehmite, up to 0.1 mm in size, were found in open cavities inside a corundum crystal from the Ratnapura area gem gravels in Ceylon. The unit cell parameters are (X-ray powder pattern): a ₀=3.695 Å b ₀=12.212 Å, c ₀=2.867 Å. The crystallographic orientation is based on X-ray single-crystal precession photographs. The crystals show the faces (it010), (001), (101), and (221). Systematic extinctions agree with the space group Amam. Optical orientation: a, b, c. Refractive indices are given. The mineral is optically positive with a large optic axial angle.     

A stable isotope study of retrograde alteration in SW Connemara,Ireland

Dalradian metamorphic rocks, Lower Ordovician meta-igneous rocks (MGS) and Caledonian granites of the Connemara complex in SW Connemara all show intense retrograde alteration. Alteration primarily involves sericitization and saussuritization of plagioclase, the alteration of biotite and hornblende to chlorite and the formation of secondary epidote. The alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs, and was the result of a phase of fluid influx into these rocks. In hand specimen K-feldspar becomes progressively reddened with increasing alteration. Mineralogical alteration in the MGS and Caledonian granites took place at temperatures 275±15°C and in the MGS P_fluid is estimated to be 1.5 kbar during alteration. The °D values of alteration phases are:-18 to-29 (fluid inclusions),-47 to-61 (chlorites) and-11 to-31 (epidotes). Chlorite ¹⁸O values are +0.2 to +4.3, while ¹⁸O values for quartz-K-feldspar pairs show both positively sloped (MGS) and highly unusual negatively sloped (Caledonian granites) arrays, diverging from the normal magmatic field on a - plot. The stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200–140°C. The retrograde fluid had D -20 to-30 in all lithologies, but the fluid ¹⁸O varied both spatially and temporally within the range-4 to +7. The fO₂ of the fluid that deposited the epidotes in the MGS varied with its ¹⁸O value, with the most ¹⁸O-depleted fluid being the most oxidizing. The D values, together with low (<0) ¹⁸O values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin. This meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration. The variation in retrograde fluid ¹⁸O values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid-rock interaction. Infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the Galway granite soon after intrusion at 400 Ma. However convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later.     

1Tc-Strontiohilgardit (Ca,Sr)2[B5O8(OH)2Cl] und seine Stellung in der Hilgarditgruppe X2/II[B5O8(OH)2Cl]

Zusammenfassung 1Tc-Strontiohilgardit (Ca, Sr)₂ [B₅O₈(OH)₂,Cl] mit Ca : Sr etwa 1 : 1 ist ein neues Mineral der Hilgarditgruppe. Fundpunkt: Reyersbausen (9° 59,7 E, 51° 36,6 N), Grube Königshall-Hindenburg, Flöz Staßfurt in sylvinitischer Ausbildung.Konstanten : triklin-pedial,a ₀=6,38 Å,b ₀=6,480 Å,c ₀=6,608 Å, =75,4°,=61,2°, =60,5°; tafelige-gestreckte Links- und Re chtskristalle, farblos, wasserunlöslich, piezoelektrisch. Härte 5–7, Dichte 2,99 g cm^–3;n =1,638,n =1,639,n =1,670; 2V =19°.Neue Daten für die Hilgarditgruppe : 2 M (Cc)-Calciumhilgardit (=Hilgardit) =4 Ca₂[B₅O₃(OH)₂Cl], Raumgruppe Cc.3Tc-Calciumhilgardit (=Parahilgardit) = 3 Ca₂[B₅O₃(OH)₂Cl]; trinklin-pedial, ₀=6,31 Å,b =6,484 Å,c ₀=17,50 Å; =84,0°,=79,6°, =60,9°.Die Polymorphiebeziehungen sind geometrisch deutbar durch eine spezielle Art der Polytropie (Stapelung von Links- und Rechtskristallen im Elementarbereich).     

Deformation and metamorphism at the base of the Helgeland nappe complex,northwest of Grong (Northern Norway)

Pelites, carbonate-silicate rocks and mafic rocks occurring at the base of the Helgeland nappe complex northwest of Grong (N. Norway) were subjected together with the crystalline basement to medium grade metamorphism and threefold deformation during Caledonian times.During the first act of deformation temperature increased and reached a maximum of 600–650°C at 6–7 Kb after the cessation of the first deformation event. At the peak of metamorphism granitic, aplitic and pegmatitic rocks were formed.During the second and third acts of deformation the temperature decreased to 500–400°C. Mylonites, formed during the second act of deformation, indicate that there was nappe movement from NW to SE. Simple shearing with direction of the main elongation parallel to the fold axes was associated with the second deformation. During the third deformation simple shearing also occurred. However, elongation took place oblique to the fold axes and the sense of rotation was opposite to that of the second deformation.

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Zusammenfassung An der Basis des Helgeland-Komplexes nordwestlich von Grong (Nord-Norwegen) wurden pelitische, kalksilikatische und basische Gesteine zusammen mit dem Kristallinen Grundgebirge in kaledonischer Zeit von drei aufeinanderfolgenden Faltungsakten erfaßt. Dabei herrschten amphibolitfazielle Temperaturen.Während der ersten Deformation stieg die Temperatur an. Das Maximum von 600–650°C wurde, bei einem Druck von 6–7 Kb, nach der ersten und vor der zweiten Deformation erreicht. Gleichzeitig intrudierten Granite, Aplite und Pegmatite. Während der zweiten und dritten Deformation sank die Temperatur wieder auf 500–400°C. Im Zuge des zweiten Deformationsaktes entstanden stellenweise Mylonite, die auf Deckenbewegungen von NW nach SE hindeuten. Zweite und dritte Deformation sind beide rotational, während der zweiten liegt die Hauptdehnungsrichtung parallel zu den Faltenachsen, während der dritten aber schräg zu ihnen. Der Rotationssinn der dritten Deformation ist dem der zweiten entgegengesetzt.

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Résumé En Norvège septentrionale, au NW de Grong, la base du complexe d'Helgeland composée de metapélites, de roches calc-silicatiques et de roches mafiques, et le soubassement cristallin de ce complexe ont subi ensemble trois actes de déformation successifs à des températures du faciès amphibolites, pendant les temps calédoniens.Durant le premier acte la température a monté. Le maximum de 600–650° C, sous une pression de 6–7 kbar, a été atteint après la fin de cette déformation et avant la deuxième; des roches granitiques, aplitiques et pegmatitiques se sont formées au cours de ce stade. Durant le deuxième et le troisième acte de déformation, la température diminuait à 500–400° C. Des mylonites, indiquant un transport des nappes du NW vers le SE, ont été formées au cours de la deuxième phase. Celle-ci est caractérisée par un mouvement rotatoire par cisaillement simple, l'élongation étant parallèle aux axes des plis. La troisième phase était égalément une phase de mouvements rotatoires, mais en sens opposé et avec un élongation oblique aux axes.

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( ) , - - , . . . 600– 650° 6 – 7 , . , . 500 – 400°. , . , , — . , .

     

Probleme der Gliederung präkambrischer,phyllitisch metamorpher Gesteinskomplexe im Hedjaz,Saudi-Arabien

Zusammenfassung Es wird ein kurzer Überblick über den komplexen Gesteinsbestand eines Gebietes im arabischen Grundgebirge des südlichen Hedjaz gegeben. Es zeigte sich, daß die tektonischen, stark überprägten und metamorphen Serien heute noch nicht in das Schema der in der Literatur genannten Serien eingebaut werden können. Diese scheinen sowohl hinsichtlich ihres stofflichen Bestandes wie auch des Zusammenhanges ihrer strukturellen und metamorphen Prägung noch zu wenig gekennzeichnet zu sein.Die im Grundgebirge weit verbreiteten Seitenverschiebungen werden kurz beschrieben und ihr Alter als wahrscheinlich spät-präkambrisch aufgefaßt.

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The paper gives a general view of the different rock series occurring in a mapped area of the basement complex in the southern Hedjaz. The predominant masses of strongly tectonized and epimetamorphic series cannot be correlated with some series, which are named already in the literature of Arabia. These latter series seem defined not sufficiently in their composition and in the relation to their structural and metamorphic development.The wrench movements, wide spread in the Arabian basement, are briefly described and defined as being probably late-precambrian.

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Résumé L'auteur donne un bref aperçu de la composition géologique complexe d'une région du soubassement arabe de l'Hedjaz du Sud. Il s'est avéré qu'à l'heure actuelle les séries fortement tectonisées et métamorphiques ne peuvent encore être intégrées au schéma des séries mentionnées par la littérature. Ces séries semblent être encore trop peu caractérisées en ce qui concerne leur composition ainsi que le rapport entre leurs caractéristiques structurelles et métamorphiques.Les failles horizontales de décrochement, qui sont très répandues dans le soubassement, sont décrites brièvement et définies comme datant probablement de la fin de l'antécambrien.

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, . , , . , . , .

     

Über die Geschwindigkeit der Krustenverkürzung in den Zentralalpen

Zusammenfassung Die alpine Krustenverkürzung (300–400 km oder mehr im Profil der Westschweiz, 400–500 km oder mehr im Profil der Ostschweiz) erfolgte in diskreten orogenen Phasen, welche durch Zeiten langsamerer Bewegung oder eigentlicher Remission getrennt waren. Während der wichtigsten Phase, an der Eozän-Oligozän-Wende, betrug die Relativgeschwindigkeit der nördlichen Platte und der südlichen Kleinplatte einige cm/a.

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Crustal shortening in the Central Alps (300–400 km or more in western Switzerland, 400–500 km or more in eastern Switzerland) occurrend in discrete orogenic phases, separated by times of slower movement or of complete stop. During the most important phase, at the turn from the Eocene to the Oligocene, the rate of relative movement of the northern plate and the southern microplate was of the order of several cm/y.

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Résumé Le raccourissement de la croûte dans les Alpes Centrales (300–400 km ou davantage en Suisse occidentale, 400–500 km ou davantage en Suisse orientale) se fit par phases orogéniques défines, séparées par des intervalles à mouvement plus lent ou même à arrêt total. Pendant la phase principale, à la fin de l'Eocène ou au début de l'Oligocène, la vitesse relative de la plaque septentrionale et de la microplaque méridionale était de l'ordre de plusieurs cm/a.

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(300–400 , , 400–500 , ) , , . , - , /.