Garnet zoning and orthopyroxene + plagioclase coronitisation

A very uncommon garnet-zoning—Ca poor centre and Ca rich margin—has been observed, in a granulite facies rock. Calculation of equilibrium at each stage of the garnet growth led to apply in this particular case, as well as for the most garnet-zoning instances, the Rayleigh fractionation model, the fractionation factor Ca being less than 1 at the beginning of the crystallization. Subsequent coronitisation, at lower P and/or higher T, involved the development of orthopyroxene and plagioclase in equilibrium with a thin (15 thick) Ca-Mg poor and Fe rich outer cuticle of the garnet: thus the garnet lattice appears to be not so refractory as previously admitted, and in most coronitisation processes involving garnet such an outer cuticle must be considered as a component of the new mineral assemblage.     

FEM × DEM modelling of cohesive granular materials: Numerical homogenisation and multi-scale simulations

The article presents a multi-scale modelling approach of cohesive granular materials, its numerical implementation and its results. At microscopic level, Discrete Element Method (DEM) is used to model dense grains packing. At the macroscopic level, the numerical solution is obtained by a Finite Element Method (FEM). In order to bridge the micro- and macro-scales, the concept of Representative Elementary Volume (REV) is applied, in which the average REV stress and the consistent tangent operators are obtained in each macroscopic integration point as the results of DEM’s simulation. In this way, the numerical constitutive law is determined through the detailed modelling of the microstructure, taking into account the nature of granular materials. We first elaborate the principle of the computation homogenisation (FEM × DEM), then demonstrate the features of our multiscale computation in terms of a biaxial compression test. Macroscopic strain location is observed and discussed.     

Fracturation tertiaire et évolution des contraintes en Bavière orientale: le Jura franconien et la forêt bavaroise (R.F.A.)

Résumé L'analyse géométrique et cinématique de la fracturation dans le Jura franconien et la bordure occidentale du Massif bohémien met en évidence les mécanismes de la tectonique cassante d'âge teriaire, essentiellement ceux des grands accidents SE-NW (lignes de Pfahl et de Franconie) qui ont présenté successivement des jeux en coulissement dextre, en faille normale et en faille inverse. Cinq états de contrainte ont été caractérisés et comparés à ceux définis antérieurement dans le Jura souabe, en liaison avec la cinématique des plaques Europe et Afrique: compression N-S, distension E-W, compression NE-SW puis E-W, distension N-S.

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The analysis of both the geometric and the kinematic cenozoic faulting in the Franconian Jura and in western Bohemia enables to characterize the mechanisms of cenozoic tectonics. More especially dextral strike-slip, normal fault and reverse fault have successively occurred along large SE-NW fault line, as the Pfahl and the Franconian fault systems. Five main stress patterns have thus been identified and then compared with those previously described in Swabian Jura. They are related to the kinematic of Europe and Africa plates, i. e.: (1) N-S compression, (2) E-W distension, (3) SW-NE compression, (4) E-W compression, (5) N-S distension.

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Zusammenfassung Durch die geometrische und kinematische Analyse der Brüche wird die tertiäre Bruchtektonik (tectonique cassante) im Fränkischen Jura und am westlichen Rand des Böhmischen Massifs belegt. Es handelt sich im wesentlichen um die großen SE-NW orientierten Störungen der Linie von Pfahl und der Fränkischen Linie, die nacheinander als dextrale Blattverschiebungen, als Normalverwerfungen und als inverse Verwerfungen wirkten. Fünf Spannungszustände können charakterisiert und mit jenen, die bereits im Schwäbischen Jura definiert wurden, verglichen werden. Sie spiegeln die verschiedenen Stadien der kinematischen Entwicklung der europäischen und afrikanischen Platte wider: Kompression N-S, Zerrung E-W, Kompression NE-SW, sodann E-W, Zerrung N-S.

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Fluid inclusions in granulites, granulitized eclogites and garnet clinopyroxenites from the Dabie–Sulu terranes, eastern China

Minor granulites (believed to be pre-Triassic), surrounded by abundant amphibolite-facies orthogneiss, occur in the same region as the well-documented Triassic high- and ultrahigh-pressure (HP and UHP) eclogites in the Dabie–Sulu terranes, eastern China. Moreover, some eclogites and garnet clinopyroxenites have been metamorphosed at granulite- to amphibolite-facies conditions during exhumation. Granulitized HP eclogites/garnet clinopyroxenites at Huangweihe and Baizhangyan record estimated eclogite-facies metamorphic conditions of 775–805 °C and ≥15 kbar, followed by granulite- to amphibolite-facies overprint of ca. 750–800 °C and 6–11 kbar. The presence of (Na, Ca, Ba, Sr)-feldspars in garnet and omphacite corresponds to amphibolite-facies conditions. Metamorphic mineral assemblages and P–T estimates for felsic granulite at Huangtuling and mafic granulite at Huilanshan indicate peak conditions of 850 °C and 12 kbar for the granulite-facies metamorphism and 700 °C and 6 kbar for amphibolite-facies retrograde metamorphism. Cordierite–orthopyroxene and ferropargasite–plagioclase coronas and symplectites around garnet record a strong, rapid decompression, possibly contemporaneous with the uplift of neighbouring HP/UHP eclogites.

Carbonic fluid (CO₂-rich) inclusions are predominant in both HP granulites and granulitized HP/UHP eclogites/garnet clinopyroxenites. They have low densities, having been reset during decompression. Minor amounts of CH₄ and/or N₂ as well as carbonate are present. In the granulitized HP/UHP eclogites/garnet clinopyroxenites, early fluids are high-salinity brines with minor N₂, whereas low-salinity fluids formed during retrogression. Syn-granulite-facies carbonic fluid inclusions occur either in quartz rods in clinopyroxene (granulitized HP garnet clinopyxeronite) or in quartz blebs in garnet and quartz matrices (UHP eclogite). For HP granulites, a limited number of primary CO₂ and mixed H₂O–CO₂(liquid) inclusions have also been observed in undeformed quartz inclusions within garnet, orthopyroxene, and plagioclase which contain abundant, low-density CO₂±carbonate inclusions. It is suggested that the primary fluid in the HP granulites was high-density CO₂, mixed with a significant quantity of water. The water was consumed by retrograde metamorphic mineral reactions and may also have been responsible for metasomatic reactions (“giant myrmekites”) occurring at quartz–feldspar boundaries. Compared with the UHP eclogites in this region, the granulites were exhumed in the presence of massive, externally derived carbonic fluids and subsequently limited low-salinity aqueous fluids, probably derived from the surrounding gneisses.     

A Twilight Zone: Identity Crisis in French Geopolitics

The paper initially describes some of the most important historical processes that have conditioned France's geopolitical position in the contemporary world. It discusses the current changes in France's geopolitics as a changing reality of international relations and as a changing discourse of scholars and experts, that reflects those real world changes. The paper focuses on French politics in Africa and on France's policy in Europe after the end of the Cold War. In Africa the French post-colonial empire with its close ties between domestic regimes, French business interests and the French state becomes unsustainable after the bipolar rivalry has been suspended. In Europe French policy can no longer be presented as either an independent view among a series of others (Europe des patries) nor as a successful effort to press French views by way of a larger European entity. The paper presents an overview of geopolitical literature written in France as a reflection of these conditions.     

A statistical method for varve verification using seasonal pollen deposition

We developed a fast, inexpensive, statistically rigorous method of varve verification that uses prospective varve layer-splitting and seasonal pollen deposition. This method can be used on any sediment that contains seasonally deposited pollen, and avoids the need for radio-isotopic, optical, or thermoluminescence dating. The method uses a χ² test and non-parametric regression, together with recorded plant bloom times from pollen traps, to assess the differences in pollen abundances in light/dark (i.e. summer/winter-spring) sediment layers. A statistical test is required because such seasonally deposited data are inherently noisy, with a low signal-to-noise ratio. To illustrate this approach, visible laminations of Lake Mina, Minnesota, USA, were assessed in two separate regions of a core spanning 900 years. Results show that the laminations were deposited annually.     

An overview of the ACE‐2 CLOUDYCOLUMN closure experiment

CLOUDYCOLUMN is one of the 6 ACE‐2 projects which took place in June‐July 1997, between Portugal and the Canary Islands. It was specifically dedicated to the study of changes of cloud radiative properties resulting from changes in the properties of those aerosols which act as cloud condensation nuclei. This process is also refered to as the aerosol indirect effect on climate. CLOUDYCOLUMN is focused on the contribution of stratocumulus clouds to that process. In addition to the basic aerosol measurements performed at the ground stations of the ACE‐2 project, 5 instrumented aircraft carried out in situ characterization of aerosol physical, chemical and nucleation properties and cloud dynamical and microphysical properties. Cloud radiative properties were also measured remotely with radiometers and a lidar. 11 case studies have been documented, from pure marine to significantly polluted air masses. The simultaneity of the measurements with the multi‐aircraft approach provides a unique data set for closure experiments on the aerosol indirect effect. In particular CLOUDYCOLUMN provided the 1st experimental evidence of the existence of the indirect effect in boundary layer clouds forming in polluted continental outbreacks. This paper describes the objectives of the project, the instrumental setup and the sampling strategy. Preliminary results published in additional papers are briefly summarized.     

Rare anthropogenic and natural particles suspended in deep ocean waters

Four hundred membrane filters from the Atlantic and Pacific deep waters have been scanned for coloured and opaque particles by a method integrating the light and the scanning electron microscopes, the electron microprobe and the micro-X-ray diffraction camera. About 40 different types of particles have been found. A tentative classification of the particles and of their morphological and chemical varieties is presented, according to their anthropogenic or natural origins. From this point of view, the particles fall into five groups: (1) particle species exclusively produced by man's activities (like brass, cobalt aluminate); (2) particles exclusively produced by natural processes (like amphibole, ilmenite); (3) particles rarely produced by natural processes, but massively so by man (like metallic copper, chromium oxide); (4) a large group of particles massively produced by nature and by man (like magnetite spherules, malachite); (5) a very small group of particles whose origin could not be attributed at present. Very few entirely new compounds from the point of view of continental mineralogy have been encountered.