Magnetospheric accretion and pre-main-sequence stellar masses

We present a method of determining lower limits on the masses of pre-main-sequence (PMS) stars and so constraining the PMS evolutionary tracks. This method uses the redshifted absorption feature observed in some emission-line profiles of T Tauri stars, indicative of infall. The maximum velocity of the accreting material measures the potential energy at the stellar surface, which, combined with an observational determination of the stellar radius, yields the stellar mass. This estimate is a lower limit owing to uncertainties in the geometry and projection effects. Using available data, we show that the computed lower limits can be larger than the masses derived from PMS evolutionary tracks for M   0.5 M. Our analysis also supports the notion that accretion streams do not impact near the stellar poles but probably hit the stellar surface at moderate latitudes.     

Some limitations of the Rfφ technique of strain analysis — Reply

The analysis presented in the discussion is statistically invalid.     

Elliptical markers and non-coaxial strain increments — discussion

Finite homogeneous strain may be deduced from the spatial distribution of initially uniformly oriented lines or planes in a rock, as recorded in a pole figure or petrofabric diagram. This paper presents a new analytic technique which is simple and rapid in practical application.     

Tableau de répartition stratigraphique des Grands Foraminifères caractéristiques du Crétacé moyen de la région Méditerranéenne

Le Groupe de Travail Européen des Grands Foraminifères présente un tableau de répartition stratigraphique de 42 espèces bien définies du Crétacé moyen de la région méditerranéenne. La répartition stratigraphique proposée pour chaque espèce est fondée soit sur des propres observations soit sur des données de la littérature supprimer et est contrôlée par la présence d'Ammonites ou de Foraminifères planctoniques.A summarizing account is presented of the deliberations of the research group for Large Foraminifers of the IGCP Project “Mid-Cretaceous Events”. Large Foraminifers are of incontestable value for dating carbonate platform sequences owing to the absence of many other diagnostic groups of organísms. A table of stratigraphical distributions for 42 species is presented.     

Monte guardia sequence: a late-pleistocene eruptive cycle on Lipari (Italy)

This paper documents a complex sequence of interbedded lapilli-fall, base-surge, and pyroclastic-flow deposits, here named the Monte Guardia sequence, that erupted from volcanic centers in the southern part of Lipari (Aeolian Island Arc). Radiocarbon data from ash-flow tuffs above and below this sequence bracket its eruption between 22,600 and 16,800 years ago. Geologic evidence, however, suggests that this single eruptive cycle had a more restricted duration of years to tens-of-years. The basis for our interpretations comes from data measured at 38 detailed sections located throughout the island. The Monte Guardia sequence rests on a series of lower rhyolitic endogenous domes in the southern part of Lipari and it covers the oldest lavas, lahars, and pyroclastic flows in the north. Only in the northeast part of the island is it covered by younger deposits which there consist of lapilli tuffs and lavas of the Monte Pilato rhyolitic cycle. The deposit ranges in thickness from more than 60 m surrounding the vents in the south to less than a few decimeters at 10 km distance in the north. Throughout most of the island the Monte Guardia sequence overlies a thin andesitic lapilli-fall layer which is a key bed for correlation. This lapilli tuff probably erupted from a volcanic center on another island of the Aeolian Arc (possibly Salina). The principal activity of the Monte Guardia sequence started with an explosion that formed a continuous breccia blanket covering most of the island. Some pumiceous blocks within this breccia are composed of alternating bands of acidic and andesitic composition suggesting that the initiation of pyroclastic activity could have been triggered by magma mixing. Typical Monte Guardia sequence consists of explosive products that grade from magmatic (pumice-fall) to phreatomagmatic (base-surge) character. The eruptive cycle is characterized by a number of energy decreasing megarhythms that start with a lapilli-fall bed and end with a base-surge set that progresses through sand-wave, massive, and planar beds. Isopach maps of the fall and surge deposits indicate that both types were directed to the northwest by prevailing winds. Existing topographic relief was an additional factor that affected the emplacement of surge products. At the end of the cycle andesitic pyroclastic flows and rhyolitic endogenous domes were emplaced above the Monte Guardia deposits near the vent.     

Development of longitudinal profiles of alluvial channels in response to base-level lowering

Degradation of alluvial channels in cohesive sediments was studied in 15 m and 20 m long flumes with a slope of 0°01 cm/cm. Degradation was initiated by lowering base level to a fixed position, and the development of the longitudinal profile of the channel is analysed through a model formulated as a heat (diffusion) equation. It is based on the equation of sediment continuity, combined with an assumption regarding sediment transport, namely that sediment discharge is linearly proportional to the channel slope. In accordance with the boundary and initial conditions imposed by the experimental setup and procedure, the basic equation is amenable to an analytical solution, which defines bed elevation at any distance and time, as a function of the amount of base-level lowering and a ‘diffusion’ coefficient. Additional problems arising from bank erosion and channel armouring are also treated successfully within the framework of the same model. The results show that in homogeneous alluvial sediments, not subject to armouring, the ultimate result of base-level lowering by a certain amount is degradation all along the channel by the same amount. The main impact of erosion is felt in the early stages after initiation of the process, and mainly near the mouth. The rate of degradation at any station along the channel reaches a peak and then slowly decreases with time, and the peak rate is attenuated with distance from the outlet. The model permits the prediction of intermediate stages of profile development at any distance from the outlet and at different times.     

Geology and volcanology of the Edd-Bahar Assoli area (Ethiopia)

The paper presents geological and petrological data on one of the alkaline ranges developed along the borders of the Afar depression (Ethiopia). These alkaline ranges occur in a position transversal to the dominant NNW trend of the spreading zones of northern and central Afar which are characterized by magmas of tholeiitic affinity. The Edd-Bahar Assoli volcanic range consists of broad fields of basic lavas and numerous spatter cones outcropping in the area extending between 13°25′ and 13°75′ lat. N and 41°38′ and 42°15′ long. E. The mineralogical assemblage and the chemical data point to an alkaline nature for this range consisting mainly of alkali olivine basalts and basalts tending to hawaiites, the most evolved terms being largely subordinate. Petrologic differences between the Assab, Edd-Bahar Assoli and Erta Ale ranges are shown. The Edd-Bahar Assoli alkaline volcanism would be related to tectonic patterns trending both from NNW-SSE to N-S and from NE-SW to E-W. The supposed similarity with the transverse structure of the equatorial Atlantic ocean would thus not completely be ascertained in this zone. In Afar, the coexistence of an axial volcanism of tholeiitic affinity with an alkaline volcanism at the margin can better be explained by models based upon the upper mantle temperature distribution in a zone under oceanization.     

The abundance of barium in stony meteorites

The concentration of Ba in 7 carbonaceous chondrites, 18 ordinary chondrites, 3 achondrites and 1 stony-iron meteorite has been determined by the stable isotope dilution technique using solid source mass spectrometry. Analysis of the C1 chondrite Orgueil indicates a small adjustment of the “cosmic” abundance of Ba to 4.2 on the Si=10⁶ abundance scale. The present work provides a more complete coverage of a number of meteorite classes than has so far been available for the abundance of Ba in stony meteorites.     

Lunar glass compositions: Apollo 16 core sections 60002 and 60004

Approximately 500 glasses between 1 mm and 125 μm in size have been analyzed from fourteen samples from the Apollo 16 core sections 60002 and 60004. The majority of glasses have compositions comparable to those found in previous studies of lunar surface soils; however, two new and distinct glass compositions that are probably derived in part from mare material occur in the core samples. The major glass composition in all samples is that of Highland Basalt glass, but it also appears that high-K Fra Mauro Basalt (KREEP) glass is more common at the Apollo 16 site than was previously thought. The relative abundance of glasses within the core samples is random in distribution: each sample is characterized by a particular assemblage and distribution of the constituent glass compositions.     

Geochemical and cosmochemical cycles involving sulfur,sulfide, sulfite and sulfate

Raman spectra of aqueous systems containing sulfur dioxide, elemental sulfur and sulfate indicate that the equilibrium between these species is catalyzed by elemental sulfur. Therefore, dynamic equilibrium can be expected under conditions prevalent on Venus, on Io and in epigenic sulfur deposits.