How did the Messinian Salinity Crisis end?

The cause of the desiccation of the Mediterranean Sea during the Messinian Salinity Crisis has been widely debated, but its re-flooding remains poorly investigated. Interpretations generally involve tectonic collapse of the Strait of Gibraltar or global sea-level rise, or even a combination of both. The dramatic sea-level fall in the Mediterranean has induced deep fluvial incision all around the desiccated basin. We investigate erosion dynamics related to this base level drop by using the numerical simulator EROS. We show that intense regressive erosion develops inevitably in the Gibraltar area eventually inducing the piracy of the Atlantic waters by an eastward-flowing stream and the subsequent re-flooding of the Mediterranean.     

Active Fire Detection for Fire Emergency Management: Potential and Limitations for the Operational Use of Remote Sensing

The use of the mid-infrared and thermal bands of sensors on board airborne platforms and satellites permits the detection of active fires on the Earths surface. This application has been available to the fire-fighting community for many years. However, limitations in the fire detection capabilities of the sensors and/or the lack of adequate re-visit frequency have prevented the use of these systems for operational forest fire-fighting. In addition to mobile systems, remote sensors positioned on fixed fire-watch towers have also been used for active fire detection. These instruments are often positioned in strategic look-out places to provide continuous monitoring of the surrounding areas. They locate fires through the detection of either hot spots (areas of increased temperature in comparison to the background) or smoke plumes produced by the fires. This article evaluates the use of existing remote sensing systems for active fire detection, with emphasis on the applicability of these systems for fire emergency management and fire-fighting. Long-range remote sensing devices on board satellites are considered, airborne systems are assessed, and short-range fire detection instruments on fixed ground platforms are reviewed. A short introduction to forthcoming satellite systems, which will be based on the combined use of several small satellites, is presented. The advantages and drawbacks of the different systems are evaluated from a fire management perspective.     

UPb emplacement and 40Ar/39Ar cooling ages of the eastern Mont-Louis granite massif (Eastern Pyrenees,France)

Zircon UPb dating by SIMS of the Mont-Louis granite yields an age of 305±5 Ma, intrepreted to reflect the igneous emplacement age of the massif. It is in agreement with the Hercynian syntectonic character of Pyrenees granite. ⁴⁰Ar/³⁹Ar on hornblende, biotite and K-feldspar permit, to estimate the massif cooling. A rapid temperature decrease (≈30 °C/Ma) is revealed from Westphalian to Late Stephanian, coeval with the emplacement of a laccolithe in the upper crust. Then, the cooling rate decreases to ≈1 °C/Ma. This would be consistent with a long time residence for the pluton from the Late Palaeozoic to the Early Cainozoic at 6–8 km depth. To cite this article: O. Maurel et al., C. R. Geoscience 336 (2004).     

Natural speciation of Zn at the micrometer scale in a clayey soil using X-ray fluorescence, absorption, and diffraction

Combined use of synchrotron-based X-ray fluorescence (SXRF), diffraction (XRD), and absorption (EXAFS) with an X-ray spot size as small as five micrometers allows us to examine noninvasively heterogeneous soils and sediments. Specifically, the speciation of trace metals at low bulk concentrations and the nature of host minerals can be probed with a level of detail unattainable by other techniques. The potential of this novel analytical approach is demonstrated by determining the Zn species in the solid phases of a pristine horizon of a clayey acidic soil (pH 4.5-5.0) having a Zn concentration of 128 mg/kg. The sample presents a differentiated fabric under the optical microscope with traces of localized manganiferous, ferriferous and argillaceous accumulations. The high chemical and textural heterogeneity of this soil offers an opportunity to identify new Zn species and to confirm the existence of others proposed from published least-squares fits of bulk averaged EXAFS spectra. As many as five to six Zn species were observed: sphalerite (ZnS), zincochromite (ZnCr₂O₄), Zn-containing phyllosilicate and lithiophorite, and Zn-sorbed ferrihydrite or Zn-phosphate, the results being less definitive for these two last species. Bulk EXAFS spectroscopy applied to the powdered soil indicated that Zn is predominantly associated with phyllosilicates, all other species amounting to < ∼10 to 20% of total zinc. The role of lithiophorite in the sequestration of zinc in soils had been inferred previously, but the firm identification of lithiophorite in this study serves as an excellent demonstration of the capabilities of combined micro-SXRF/XRD/EXAFS measurements. The micro-EXAFS spectrum collected in an area containing only phyllosilicates could not be simulated assuming a single Zn structural environment. Two distinct octahedrally-coordinated crystallographic sites (i.e., two EXAFS components) were considered: one site located within the phyllosilicate structure (isomorphic cationic substitution in the octahedral sheet) and another in the interlayer region in the form of a Zn-sorbed hydroxy-Al interlayered species. This second subspecies is less certain and further investigation of the individual EXAFS spectrum of this component is needed to precise its exact nature and the uptake mechanism of zinc in it.     

Interactive Statistical Analysis of Complex Mantle Flows with the Web

Up to now, all of the figures in mantle convection literature have been presented in a static manner, where the fields at one scale are shown on a printed page . This is no longer possible with the spatial resolution increasing at an ever rising clip and the appearance of the issue of multi-scale structures. Because of the onslaught of data-flooding and the growing complexity of strongly time-varying physical fields from compressible mantle convection, such as the adiabaticity, and other thermo dynamical heating functions, we can no longer afford to display and look at the results in the same static way as in a book. We have developed a new approach for interrogating data coming out from numerical simulations. This is based on an interactive two-dimensional map which is used over the WEB with a client-server paradigm. We have applied this to investigate mantle convection flows in both two-and three-dimensional situations. The distributions of thermal anomalies found are no longer Gaussian but sometimes have long tails, especially near the edges of plume heads. The same is also found for the distribution of mechanical heating, which can be quite skewed. Our experiences with this new interactive mode of data-query have shown both the educational and scientific importance of using the world wide web media to quiz handily the data taken from large-scale numerical simulations.     

On the Central-African metallogenetic province

The copper, tin and gold deposits of Central Africa occupy the median part of an archaïc-paleozoic mountain ring extending from the Lower Congo to the Central Highlands and to South West Africa. Most of the metalliferous zone is sandwiched between the Western Rift Valley and the Karroo transgression of the Congo Basin. This “ribbon” is 2500 miles long, width varying from 100 to 400 miles. Deposits seem to follow ancient and often reccuring trends. At least three pre-cambrian mineralizing cycles should be distinguished:

$$\begin{array}{*{20}c} {\begin{array}{*{20}c} {epoc} \\ {1.Kabalian} \\ {2.Urundian} \\ {3.Katangian} \\ \end{array} } & {\begin{array}{*{20}c} {metal} \\ {Au} \\ {Sn,Nb,W,Au} \\ {Cu,Co,U,Zn} \\ \end{array} } & {\begin{array}{*{20}c} {region} \\ {Ituri,Uele,Kivu,Tanganyika} \\ {Uganda,Ruanda,Maniema,Katanga} \\ {Katanga,Rhodesia} \\ \end{array} } \\ \end{array}$$     

Fabric asymmetry and shear sense in movement zones

Asymmetry between lattice preferred orientation and shape fabrics is commonly observed in microstructural studies of many deformed mineral aggregates (e. g. ice, carbonate rocks, peridotites and quartzites). Theoretical predictions are limited by the nature of the models available and more can be gained by discussion of the mechanisms which give rise to such asymmetry in specific natural and experimental situations. Asymmetry is often related to the sense of shear but there are other factors to be considered as well. It is concluded that fabric asymmetry can be a useful tool for the analysis of flow regimes in naturally deformed rocks, as long as the conditions prerequisite to successful application of this technique can be shown to have existed, and cognizance is taken of the limitations of the technique.     

The crystal chemistry of roméite

Roméite (Ca, Fe, Mn, Na)₂(Sb⁵⁺, Ti⁴⁺)₂(O, OH, F)₇ is a rare mineral found in metamorphic iron-manganese deposits and in hydrothermal Sb-bearing veins. It is isostructural with the pyrochlore-group minerals of the general formula A_2–mB₂X_6–wY_1–n · pH₂O. The pyrochlore-group minerals are important Nb and Ta ores, and are also used as an actinide host phase in␣radioactive waste. The crystal chemistry of roméite from the type locality Praborna (Italy), from Massiac (France), and from four newly discovered localities in␣the Swiss Alps, and of “lewisite”, a questionable species related to roméite from Tripuhy (Brazil), is compared to that of pyrochlore. A wide range of substitutions has been observed including (1) independent substitutions on the A- and B-sites, and (2) coupled substitutions between the A- and B- and between the A- and Y- sites. Only the roméite from Massiac, derived from weathering of stibnite, contains significant H₂O (up to 14 wt %). The A-site vacancies in roméite appear to be controlled by the primary conditions of crystallization, and not by post-crystallization alteration. The Y-site chemistry of roméite varies from locality to locality; it can be dominated by F, OH, or be fully vacant. The “lewisite” octahedral crystals studied are a sub-microscopic mixture of roméite with a mineral structurally related to pyrochlore, which grows at the expense of roméite. Received: 5 March 1996 / Accepted: 18 October 1996