Etude des inclusions fluides du système N2-CO2 de dolomites et de quartz de Tunisie septentrionale. Données de la microcryoscopie et de l'analyse à la microsonde à effet Raman

Optical and analytical studies were performed on 400 N₂ + CO₂ gas bearing inclusions in dolomites and quartz from Triassic outcrops in northern Tunisia. Other fluids present include brines (NaCl and KCl bearing inclusions) and rare liquid hydrocarbons. At the time of trapping, such fluids were heterogeneous gas + brine mixtures. In hydrocarbon free inclusions the $\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}$ mole ratio was determined using two different non-destructive and punctual techniques: Raman microprobe analysis, and optical estimation of the volume ratios of the different phases selected at low temperatures. In the observed range of compositions, the two methods agree reasonably well.The N₂ + CO₂ inclusions are divided into three classes of composition: (a) $\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}\text{> 0,57}$: Liquid nitrogen is always visible at very low temperature and homogenisation occurs in the range ?151°C to ? 147°C (nitrogen critical temperature) dry ice (solid CO₂) sublimates between ?75°C and ?60°C; (b) $\text{0,20 <}\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}\text{? 0,57}$: liquid nitrogen is visible at very low temperature but dry ice melts on heating; liquid and gas CO₂ homogenise to liquid phase between ?51°C to ?22°C; (c) $\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}\text{? 0,20}$: liquid nitrogen is not visible even at very low temperature (?195°C) and liquid and gas CO₂ homogenise to liquid phase between ?22°C and ?15°C. The observed phases changes are used to propose a preliminary phase diagram for the system CO₂-N₂ at low temperatures.Assuming additivity of partial pressures, isochores for the CO₂-N₂ inclusions have been computed. The intersection of these isochores with those for brine inclusions in the same samples may give the P and T of trapping of the fluids.     

Analysis of Standard Reference Materials for Zr,Nb, Hf and Ta by ICP-MS after Lithium Metaborate Fusion and Cupferron Separation*

Results are presented of the determination of Zr, Nb, Hf and Ta in 74 standard reference materials by inductively coupled plasma mass spectrometry (ICP-MS). Samples are decomposed by fusion with lithium metaborate and the analytes are separated prior to analysis by precipitation of their cupferrates. Calibration is made using synthetic solutions and internal standardization with Ru (for Zr and Nb) and Re (for Hf and Ta). Accuracy is assessed by comparison with recommended values and precision is evaluated by replicate analyses of five SRMs.     

Radiation-enhanced release of uranium from accessory minerals in crystalline rocks

Implantation of low energy (~ 1 keV/amu) Pb ions, simulating α-recoils, greatly increases the dissolution rate of U-bearing minerals in aqueous solutions above a critical dose $\text{~5 × 10}{}^{12}\text{ions·cm}{}^{\mathrm{?2}}$. A Monte-Carlo code of etching indicates that this phenomenon corresponds to a percolation threshold due to the accumulation of ion-induced defects above a critical concentration. Such a radiationenhanced dissolution could be produced by α-recoil damage in U-rich accessory minerals of sufficient U-content and/or age. Therefore, this process could be the primary source of this element in the formation of U ores associated with crystalline rocks.     

The fossil vertebrates from Lano (Basque Country, Spain); new evidence on the composition and affinities of the Late Cretaceous continental faunas of Europe

A newly discovered fossil locality at Lano (Basque Country) has yielded a vertebrate assemblage of probably Maastrichtian age comprising fishes, amphibians, reptiles and mammals. It considerably enlarges our knowledge of the Late Cretaceous continental faunas of Europe, hitherto based on a much less complete record. Some taxa are recorded for the first time in Europe, and the fauna also contains the oldest known representatives of some groups (amphisbaenians, salamandrids). The Lan assemblage reveals an original fauna comprising both forms related to Asian and North American groups and elements with Gondwanan affinities.     

Lizards and snakes from the late Miocene hominoid locality of Ravin de la Pluie (Axios Valley,Greece)

We here describe lizards and snakes from the late Miocene (MN 10) of Ravin de la Pluie, near Thessaloniki, Greece, a locality widely known for its hominoid primate Ouranopithecus macedoniensis. The new finds comprise two large-sized lizards (a probable anguine and a varanid) and two snakes (an elapid and a small-sized “colubrine”). Even if the material is represented by few specimens, this is the first record of squamates from the late Miocene MN 10 biozone of southeastern Europe and the third only for the whole continent. The importance of the varanid vertebrae for systematic attributions is discussed. The new varanid limb elements described herein rank among the few such specimens in the fossil record of monitor lizards. Judging from the new and previously published varanid appendicular material, we suggest that Neogene monitor lizards from Europe possessed comparatively short and robustly built limbs. Distinctive scars on one of the limb elements are interpreted as bite marks of a predator or scavenger, offering insights on the palaeoecology of the herpetofauna of the locality.     

Quaternary strike-slip faults in southeastern spain

The Gibraltar Arc (Western Mediterranean Sea) is traversed by a NE-trending fault system that extends from northern Morocco to southeastern Spain. In this area, three main faults (the Carboneras, Palomares and Alhama de Murcia faults) have been active in Quaternary time. The faults are characterized by left-lateral strike-slip motion. The Quaternary faulting and current seismicity in this part of the Meditterranean area are related to a collision-type tectonics produced by the northwestward relative motion of the African Plate toward the European Plate.     

Les Vertébrés de la Partie Moyenne du Crétacé en Europe

Les gisements de Vertébrés de la partie moyenne du Crétacé en Europe sont peu nombreux, et des groupes importants (notamment les Mammifères) y sont encore inconnus. Les poissons sont mieux représentés que les tétrapodes, et plus utilisables d'un point de vue biostratigraphique. Pour un certain nombre de groupes de Vertébrés, la partie moyenne du Crétacé semble correspondre à un renouvellement faunique important.In Europe, fossil vertebrate localities in the middle part of the Cretaceous are not numerous, and some important groups (notably mammals) are still unknown there. Fishes are better represented than tetrapods, and more useful from a biostratigraphic point of view. For several groups of vertebrates, the middle part of the Cretaceous seems to correspond to an important faunal renewal.     

The Kenna ureilite: an ultramafic rock with evidence for igneous,metamorphic, and shock origin

The Kenna ureilite was found in February, 1972 near the town of Kenna, Roosevelt County, New Mexico U.S.A., weighed 10.9 kg, and measured 26.7 × 14.7 × 14.2 cm; it is the seventh known ureilite. The meteorite is composed of xenoblastic olivine (Fo_79.2), commonly rimmed by forsterite (Fo₉₉), and pigeonite (En₇₃Wo₉Fs₁₈), in a volumetric ratio of 3:1, set in a matrix of three carbon polymorphs (graphite, lonsdaleite, and diamond) plus nickel-iron metal and troilite. Some thin metalliferous veins penetrating silicate grains contain secondary inclusions of melt with high-calcium clinopyroxene (high-Ca, Mg-rich augite to augite), andesine, K-feldspar, chromite, and siliceous CaO- and alkali-rich glasses of variable compositions.Textural, mineralogical and fabric information suggest a complex history for Kenna, involving igneous, metamorphic and shock processes. The rock appears to have originated as an ultramafic cumulate whose texture and structure was modified by adcumulus processes and by solution and redeposition in a weak deviatoric stress field. A strong mineral elongation lineation was produced during this high-temperature phase accompanied by mild plastic deformation of olivine on the system 0kl[100]. Superimposed on this original texture and fabric are processes resulting from light to moderate (50–250 kbar) shock deformation, as manifested by fracturing of the silicates, slip parallel to (001) in olivine, and twin and translation gliding parallel to (100) in the clinopyroxene. Lonsdaleite and diamond probably formed during this shock phase, which may be associated with the break-up of the parent body, but the relative time of introduction of the carbon-rich matrix is still unresolved.     

The vourinos ophiolite complex, Greece: The tectonite suite

Classical structural analysis, in combination with new techniques including pyroxene thermobarometry and recrystallized-grain- and subgrain-size paleopiezometry, has been used to deduce the tectonic history of the Vourinos Ophiolite Complex, Greece. Results can be used to infer the variation with depth of differential stress in the upper mantle and indicate that these rocks were subjected to an initial stress level of 10–100 bar over a depth interval from 100 to 40 km, respectively. Subsequently, they underwent mylonitization, associated with stresses of about 2500 bar at 30 km depth. Rocks equilibrated at the deepest levels commonly have the highest structural positions within the ultramafic tectonites and also show appreciable Al depletion. Lack of annealing recrystallization in the mylonitic rocks, together with low stress levels and an abnormally high pyroxene geotherm for the Complex lead to the interpretation of the Complex being the remnant of a mantle diapir, with an overlying magma chamber, located at a spreading ridge.