The product spectra of gravity and barometric pressure in Europe

A total of 111 000 hourly values of gravity and barometric pressure from stations in Europe is analysed. The data consist of two sets of records from Brussels, an early set of 36 000 h length and a more recent set of 21 000 h length, a set of records from Bad Homburg of 24 000 h length, and a set of records from Strasbourg of 30 000 h length. All of the gravity measurements were made with similar superconducting instruments and the pressure data were recorded simultaneously at each superconducting gravimeter site. The four sets of records have different time bases, and to bring out common features and suppress individual station systematic errors, the product spectrum is introduced. Spectral density estimates are first computed for a common spectral window for each record, and the product spectrum is formed by multiplying individual spectral estimates across records. The cumulative distribution function is found for the product spectrum and confidence intervals are calculated from it by iteration. The product spectrum in gravity reveals a triplet of resonances in the subtidal band which are shown by an automated computer search to be uniquely associated with the translational modes of the solid inner core. The product spectrum in barometric pressure clearly reveals the first 10 solar heating tides in the atmosphere, but otherwise does not show common features with the gravity product spectrum. In particular, the triplet of resonances in the subtidal band of the gravity product spectrum do not show up in the product spectrum of barometric pressure, climinating the atmosphere as their source.     

Les tholeiites a affinité alcaline du secteur ouest du Siroua (Anti-Atlas central, Maroc): temoins d'une distension au Néoproterozoïque

The Upper Proterozoic granitoids of the western part of the Siroua Massif (central Anti-Atlas, Morocco) are cut by doleritic dykes injected along submeridian and equatorial directions. These dykes were emplaced before deposition of late Neoproterozoic formations (PIII). According to and incompatible element ratios, these dolerites constitue two discrete chemical groups unrelated to orientation and thickness. They are both enriched in large ion lithophile elements, Zr, Th and light rare earth elements, and correspond to continental tholeiites displaying an alkaline affinity. This alkaline affinity is also confirmed by clinopyroxene and amphibole chemistry. Emplacement of these doleritic dykes occurred under an extensional regime active in the Anti-Atlas range during the Upper Proterozoic.     

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.     

Spinel-olivine geothermometry in peridotites from ultramafic complexes

An empirical calibration of the spinel-olivine geothermometer (Evans and Frost, 1975) is attempted and applied to parageneses of lherzolitic rocks. In ultramafic complexes, most of the derived temperature estimates range between 700 ° and 850 °C, and appear generally lower than those given by other geothermometers, based upon Ca or Al contents of coexisting pyroxenes. A comparison of the different thermometric data in two well studied occurrences, the Ronda ultramafic complex and the San Carlos xenolith field, suggests that differential rates of diffusion and recrystalization may account for the large range of temperatures (between 700 ° and 1200 °C) determined by various mineral geothermometers in peridotites. The equilibrium exchange of Mg and Fe between spinel and olivine would be the fastest one and would continue effectively during the cooling down to relatively low temperatures, while other exchange reactions used as geothermometers in peridotites, like partitioning of Ca and Al in coexisting pyroxenes, are blocked at higher temperatures.     

Determination of the mean principal directions of stresses for a given fault population

New methods of determination of stress axes, from field measurements of the orientations of faults and slickenslides, are discussed. Results show that the approximation which assumes that relative motion along any fault is controlled by a single common mean stress tensor is valid.     

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.     

Sediment yield and storage variations in the Négron River catchment (south western Parisian Basin,France) during the Holocene period

In the Négron River catchment area (162 km²), surface‐sediment stores are composed of periglacial calcareous ‘grèze’ (5 × 10⁶ t) and loess (21 × 10⁶ t), and Holocene alluvium (12·6 × 10⁶ t), peat (0·6 × 10⁶ t) and colluvium (18·5 × 10⁶ t). Seventy‐five per cent of the Holocene sediments is stored along the thalwegs. Present net sediment yield, calculated from solid discharge at the Négron outlet, is low (0·6 t km^?2 a^?1) due to the dominance of carbonate rocks in the catchment. Mean sediment yield during the Holocene period is 7·0 t km^?2 a^?1 from alluvium stores and 7·6 t km^?2 a^?1 from colluvium stores. Thus, the gross sediment yield during the Holocene period is about 18·7 t km^?2 a^?1 and the sediment delivery ratio 3 per cent. The yield considerably varies from one sub‐basin to another (3·9 to 24·5 t km^?2 a^?1) according to lithology: about 25 per cent and 50 per cent of initial stores of periglacial grèze and loess respectively were reworked during the Holocene period. Sediment yield has increased by a factor of 6 in the last 1000 years, due to the development of agriculture. The very high rate of sediment storage on the slope during that period (88 per cent of the yield) can be accounted for by the formation of cultivation steps (‘rideaux’). It is predicted that the current destruction of these steps will result in a sediment wave reaching the valley floors in the coming decades. Subboreal and Subatlantic sediments and pollen assemblages in the Taligny marsh, where one‐third of the alluvium is stored, show the predominant influence of human activity during these periods in the Négron catchment. Copyright © 2002 John Wiley & Sons, Ltd.