Na-rich carbonate inclusions in perovskite and calzirtite from the Guli intrusive Ca-carbonatite,polar Siberia

Carbonate phases, some rich in Na₂O and comparatively rich in SrO and BaO, occur as inclusions in perovskite and calzirtite (Ca₂Zr₅Ti₂O₁₆) in the carbonatite of the Guli complex, Siberia. This is the first record of alkali carbonates, akin to nyerereite [Na₂Ca(CO₃)₂], in plutonic igneous rocks. The inclusion populations suggest that the parental magma of the complex was Ca-rich but developed Na-rich differentiates during the latest stages. This points to the dominant calcic carbonatites of the complex not being derivatives of alkali-rich parental carbonatites. These alkali-rich carbonate inclusions (and rare inclusions of djerfisherite) have been preserved due to the resistance of perovskite and calzirtite to processes of leaching, hydrothermal alteration and weathering.     

High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle

Synthetic spinel harzburgite and lherzolite assemblages were equilibrated between 1040 and 1300° C and 0.3 to 2.7 GPa, under controlled oxygen fugacity (f _{O 2}). f _{O 2} was buffered with conventional and open double-capsule techniques, using the Fe−FeO, WC-WO₂-C, Ni−NiO, and Fe₃O₄−Fe₂O₃ buffers, and graphite, olivine, and PdAg alloys as sample containers. Experiments were carried out in a piston-cylinder apparatus under fluid-excess conditions. Within the P-T-X range of the experiments, the redox ratio Fe³⁺/ΣFe in spinel is a linear function of f _{O 2} (0.02 at IW, 0.1 at WCO, 0.25 at NNO, and 0.75 at MH). It is independent of temperature at given Δlog(f _{O 2}), but decreases slightly with increasing Cr content in spinel. The Fe³⁺/ΣFe ratio falls with increasing pressure at given Δlog(f _{O 2}), consistent with a pressure correction based on partial molar volume data. At a specific temperature, degree of melting and bulk composition, the Cr/(Cr+Al) ratio of a spinel rises with increasing f _{O 2}. A linear least-squares fit to the experimental data gives the semi-empirical oxygen barometer in terms of divergence from the fayalite-magnetite-quartz (FMQ) buffer:

Geochemical specialization of the tin-bearing granitoid massifs of NW Bohemia

The geochemistry of Hercynian tin-bearing granitoid massifs of the Krune hory Mts. (Erzgebirge), Slavkovský les Forest (Kaiserwald) and Smriny (eastern Fichtelgebirge) is compared by statistical processing of 270 analyses including a wide spectrum of major and trace elements. Seven different types of granites are distinguished. Out of these, five types represent the successive differentiation of the largest massif of NW Bohemia: the Karlovy Vary (Karlsbad) massif. This comprises strongly differentiated peraluminous granites evolving towards extreme Li-Rb-Cs-F-and Sn-enrichment in the youngest members, which are albite-topaz-zinwaldite lithium granites. The sixth and seventh types are different from the former by their location in the eastern Krune hory and tectonic setting, and they display geochemical features of anorogenic granites: they are metaluminous albite-zinwaldite granites with marked enrichment of Nb, Y, and HREE in addition to Li, Rb, Cs, F and Sn, indicating contamination by sub-crustal material. Sn-W mineralizations, including flat peri-contact greisen bodies, steep greisen veins and tourmalinized phyllites, are all intimately associated with the most strongly differentiated granites — the Li-granite and the Cinovec-granite respectively.     

On the practice of estimating fractal dimension

Coastlines epitomize deterministic fractals and fractal (Hausdorff-Besicovitch) dimensions; a divider [compass] method can be used to calculate fractal dimensions for these features. Noise models are used to develop another notion of fractals, a stochastic one. Spectral and variogram methods are used to estimate fractal dimensions for stochastic fractals. When estimating fractal dimension, the objective of the analysis must be consistent with the method chosen for fractal dimension calculation. Spectal and variogram methods yield fractal dimensions which indicate the similarity of the feature under study to noise (e.g., Brownian noise). A divider measurement method yields a fractal dimension which is a measure of complexity of shape.     

Evaluation of ferrous and ferric Mössbauer fractions

The Mössbauer fractions f for various ferrous- and/or ferric-containing oxides and oxyhydroxides, silicates and carbonates were evaluated from the experimental temperature dependence of their center shifts, using the Debye approximation for the second-order Doppler shift. It is concluded that ferrous ions exhibit a lower fraction as compared to ferric ions. Using standard mixtures of -Fe₂O₃ with selected Fe²⁺ or Fe³⁺ compounds, it is found that the calculated Fe³⁺ f values are somewhat overestimated with respect to those of Fe²⁺. Possible explanations for this shortcoming are discussed and it is suggested that a different temperature dependence of the intrinsic isomer shift is the most likely reason. This suggestion is corroborated by analyses of hematite and hedenbergite data which are available for temperatures up to 900 K and 800 K respectively.     

Littoral '92

Reports

Littoral '92     

The demographic responses to famine: The case of China 1958–61

Pre-1949 China was The Sick Man of Asia, The Land of Famine. In 1949 Mao brought the communists to power and in the re-ordered world, all such problems were supposedly overcome — but not so. Thirty years ago China suffered one of the world's worst famines. Over the four years 1958–61, China suffered some 25–30 million more deaths and experienced some 30–35 million fewer births than might have been expected under normal conditions. Yet for almost a quarter of a century there would be few, outside of China, who were aware of the existence let alone the dimensions of the disaster. Access to Chinese census data since the mid-1980s has permitted a preliminary analysis of the demographic impact of the famine.Abbreviations JPRS-CEA-81-128 Joint Publications Research Service, China Economic Affairs Report 128, 1981 - JPRS-CPS-85-028 Joint Publications Research Service. China Report, Political, Sociological & Military Affairs 28, 1985     

Periodic Hartree-Fock study of minerals: Tetracoordinated silica polymorphs

Periodic Hartree-Fock STO-3G calculations have been performed on several tetracoordinated silica polymorphs: low and high quartz, low and idealized high cristobalite and prototype tridymite. The optimized structural parameters are in overall good agreement with experimental data. In the particular case of -quartz, the SiO₄ tetrahedra are found to be irregular. The optimized values of the two different SiO bond lengths are respectively 1.608 Å and 1.613 Å. The potential energy versus tilt angle curves suggest a picture of the high temperature phases in terms of delocalized oxygen atoms which is consistent with a disordered structure. Finally, the bonding in silica polymorphs is discussed from electron density maps and Mulliken population analysis.     

A layered basic intrusion,deformed and metamorphosed in granulite faciès of the Sri Lanka basement

A layered basic intrusion has been found in the Central Granulite Belt of the Sri Lanka continental basement. It intruded parallel to bedding, before all or early during deformation of neighbouring metasediments. Deformation, affecting metasediments and the intrusion alike, includes flattening to c. 1/20 of the original thickness and NNW-stretching to c. 20 times the original length. The intrusion is now 170–300 m thick. Most of the deformation was acquired under granulite facies metamorphism. The intrusion was then folded, still at high T, by a large F₄-synform with an axis parallel to str₁ and a steep axial plane. A steep axial plane cleavage and minor folds are related to this big fold. Stretching continued along its axis. Late during formation of this fold a granite intruded, mainly following S₄ cleavage planes. The intrusion shows a homogeneous gabbroic series at the bottom, followed upwards by a differentiated and layered series. A thin sequence of ultramafic rocks occurs near the middle. This indicates multiple melt-injection. More homogeneous partly biotite-bearing amphibolites form the top of the succession. Magmatic layering is well preserved, but no magmatic minerals or grain fabrics have escaped deformation or metamorphism. Static annealing under granulite facies conditions outlasted all deformation and was accompanied and followed by the beginning of cooling. Hornblende-Plagioclase coronas formed round garnets at this stage. Geochemical work, carried out by STOSCH (1991) on our samples, confirms the cumulate nature of the rocks.

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Zusammenfassung Eine geschichtete Basische Intrusion wurde im Central Granulite Belt der tiefen, kontinentalen Kruste Sri Lankas entdeckt. Sie intrudierte parallel zur Schichtung in benachbarte Sedimente, vor aller oder sehr früh in deren Deformation. Die Deformation, die Sedimente und die Intrusion in gleicher Weise betraf, führte zu Plättung auf das ca. 1/20 der Ausgangsdicke und zu NNW-Streckung auf das ca. 20fache der Ausgangslänge. Heute ist die Intrusion 170–300 m dick. Der Hauptteil der Deformation wurde unter Granulit-Fazies-Bedingungen erworben. Noch bei hoher T wurde die Intrusion durch eine große F₄-Falte gefaltet. Deren Achse liegt parallel der Streckungsrichtung, stri, ihre Achsenebene ist steil. Eine steile, Achsenebenen-parallele S₄-Schieferung und kleinere Falten entstanden mit ihr. Während der Bildung dieser Falte hielt die Streckung parallel ihrer Achse an. Spät während ihrer Bildung intrudierte ein Granit. Er folgt im wesentlichen S₄. Die Intrusion beginnt unten mit einer homogenen, gabbroiden Serie. Nach oben folgt eine differenzierte, geschichtete. Ein dünnes Paket ultramafischer Lagen erscheint nahe der Mitte. Es weist auf multiple Schmelz-Zufuhr hin. Homogenere Amphibolite, teils mit Biotit, bilden den obersten Teil. Magmatischer Lagenbau ist gut erhalten, lokal mit Gradierung. Magmatische Minerale oder Korngefüge haben Deformation und Metamorphose nicht überlebt. Statische Temperung unter Granulit-Fazies-Bedingungen überdauerte alle Deformation. Sie beginnt und dauert an bei bereits sinkender T. Hornblende-Plagioklas-Koronas bilden sich in diesem statischen Endstadium. STOSCH (1991) untersuchte unsere Proben von der Intrusion geochemisch. Er bestätigte die Kumulatnatur der Gesteine.

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Résumé Une intrusion basique litée a été découverte dans la ceinture centrale granulitique du socle continental du Sri Lanka. L'intrusion s'est effectuée parallèlement à la stratification, avant la déformation des métasédiments encaissants ou tout au début de celleci. La déformation, qui affecte à la fois les métasédiments et l'intrusion, comporte un aplatissement jusqu'à ± 1/20 de l'épaisseur d'origine, et un allongement de ± 20 fois en direction NNW. L'intrusion présente actuellement une épaisseur de 170 à 300 m. La plus grande part de la déformation a été acquise dans les conditions du faciès des granulites. L'intrusion a ensuite été plissée, toujours à haute T, en un large synforme F₄ dont l'axe est parallèle à l'allongement stri et dont le plan axial est vertical. Ce grand pli est accompagné d'une schistosité S₄ plan-axiale redressée et de plis secondaires. L'allongement s'est poursuivi parallèlement à son axe. A la fin de la formation de ce pli, un granite s'est intrudé, qui suit en gros S₄. L'intrusion comporte à sa base une série gabbroïque homogène, suivie vers le haut par une série litée et différenciée. Elle contient, vers son milieu, une intercalation mince de roches ultramafiques. Ceci implique des injections répétées de magma. Le sommet est formé d'amphibolites homogènes partiellement biotitiques. Le litage magmatique est bien conservé, mais aucun minéral ou fabrique magmatique n'a échappé à la déformation et au métamorphisme. Un recuit statique dans les conditions granulitiques a suivi la déformation; il a été accompagné et suivi par le début du refroidissement. A ce stade, des couronnes à hornblende-plagioclase se sont formées autour des grenats. Une étude géochimique, effectuée en 1991 par Stosch sur nos échantillons confirme le caractère de cumulat des roches.

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- . , . , , 1/20 20- NNW . 170–300 . . F₄, str₁, . , S₄, . . . S₄. , , . . , , . coxpa . , .. . , . . . . STOSCH (1991) .

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List of abbreviations ss sedimentary bedding - s₁ first cleavage, plane of first flattening - str₁ Direction of first stretching; although L is usually used for lineations of different kind, including stretching, we use this term to point out that extension is proved in each case - F₂ second folds = first folds folding s₁ - s₂ second cleavage or plane of flattening - F₃ third folds - s₃ third cleavage or plane of flattening - F₄ fourth folds, folding s_1,2,3 and F_1,2,3 - s₄ fourth cleavage or plane of flattening - str₄ direction of fourth stretching - F_5,6 fifth and sixth folds - gf(m) granulite facies (metamorphism) - af(m) amphibolite facies (metamorphism) - KNa-f KNa-feldspar - pg plagioclase - f feldspar - opx orthopyroxene - cpx clinopyroxene - px pyroxene - hb hornblende - bi biotite - cc calcite - do dolomite - qz quartz - mt magnetite     

Evolution of nappes in the eastern margin of the Bohemian Massif: a kinematic interpretation

The entire pile of nappes in the eastern margin of the Bohemian massif is characterized by two stages of Variscan nappe emplacement each exhibiting a different kinematic and metamorphic evolution.The older emplacement (D1) probably occurred around 350-340 Ma ago and was synmetamorphic. The nappes show a typical systematic superposition of higher grade metamorphic units over lower grade ones. Thus, the crystalline complexes showing a HT-MP Barrovian imprint (Svratka allochthonous unit and Moldanubicum) were thrust over an intermediate unit affected by MTMP recrystallization (Bíte orthogneiss and its country rock), and at the base of the D1 nappe pile the Inner Phyllite Nappe (Biý Potok Unit) is characterized by LT/LP metamorphism.The second stage of tectonic evolution (D2) is characterized by a thin-skinned northward-oriented nappe emplacement that occurred under LT-LP conditions dated at 320-310 Ma. The whole nappe sequence formed during the first tectonometamorphic period (D1) was transported northward over the autochthonous »Deblín polymetamorphic and granitic complex« of Upper Proterozoic age and its Devonian sedimentary cover with very low metamorphism. During this second tectonic event the Brno granite massif (580 Ma) was only marginally incorporated in the Variscan nappe tectonics which resulted in kilometer-scale cover and basement duplexes. The tectonic evolution of the nappe pile ended with stage D3, represented by large- to medium-scale east-vergent folds with limited displacement.

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Zusammenfassung Der Deckenbau am Ostrand der Böhmischen Masse erfolgte in zwei aufeinanderfolgenden Stadien, die sich sowohl in ihrer Kinematik als auch in ihrer Metamorphoseentwicklung deutlich voneinander unterschieden.Die ältere Phase (D1 ca. 350-340 Ma) ist durch synmetamorphe Überschiebungen charakterisiert. Sie führt zu einer metamorphen Inversion der überschobenen Deckeneinheiten, so daß generell hohe metamorphe Einheiten schwach metamorphe tektonisch überlagern. Der Svratka Komplex und das Moldanubikum als hangendste Decken sind durch MP/HT Paragenesen vom Barrow-Typ gekennzeichnet. Beide Einheiten sind auf den MP/MT-metamorphen Bite-Gneis und seine Rahmengesteine überschoben. Die Bílý potok Einheit als liegende Decke zeigt nur noch eine LP/ LT Regionalmetamorphose.Das jüngere Stadium (D2 ca. 320-310 Ma) ist durch eine Thin-skinned Tektonik mit nordvergentem Deckentransport unter LP/LT Bedingungen charakterisiert. Der gesamte, invers metamorphe D1-Deckenstapel wird dabei nach N über den autochtonen Deblín Komplex bzw. seine devonische Sedimenthülle überschoben.Das Brno Granit Massiv (580 Ma) wird nur randlich in diesen variszischen Deckenbau einbezogen. Die tektonische Entwicklung endet mit einem mittel bis großräumigen E-vergenten Faltenbau (D3 phase).

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Résumé L'empilement des nappes a la bordure orientale du Massif de Bohème est caractérisé par deux stades de mise en place présentant différentes évolutions cinématiques et métamorphiques.La tectonique majeure de mise en place des nappes crustales intervient lors d'un métamorphisme de type barrowien, calé autour de 350-340 Ma. L'empilement qui en résulte montre une superposition systématique d'unités à fort degré de métamorphisme sur des unités moins métamorphiques. Ainsi les complexes cristallins, montrant des reliques de métamorphisme de haute à moyenne pression-haute température (unités cristallines de Svratka et du Moldanubien), chevauchent une unité intermédiaire affectée par un métamorphisme de moyenne à basse pression-moyenne température (l'orthogneiss de Bíte et son encaissant). A la base de cette pile édifiée durant la tectonique D1, l'unité des phyllites internes (unité de Bílý potok) est caractérisée par un métamorphisme de basse témperature-basse pression.Le second stade D2 de l'évolution tectonique est caractérisé par une tectonique pelliculaire à vergence nord datée à 320-310 Ma. L'empilement résultant de D1 est ainsi transporté vers le nord, au dessus du complexe autochtone d'âge protérozoïque supérieur (groupe de Deblín) et sa couverture sédimentaire dévonienne très faiblement métamorphisée.Le massif granitique de Brno (580 Ma) n'est que marginalement incorporé à cette tectonique de nappe varisque. Ceci se traduit par des duplex socle-couverture d'échelle plurikilométrique. L'évolution tectonique s'achève lors d'une troisième phase, marquée par de grands plis à vergence est. Le déplacement associé est alors d'amplitude limitée.

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