Un nouveau critere de sens de mise en place dans une caisse filonienne: Le “pincement” des mineraux aux epontes : Orientation des minéraux dans un magma en écoulement

The flow of a magma into a dike, sill, laccolite, pipe or batholith leads to a preferential orientation of crystals in the magma. A study by computer simulation has brought to light certain types of fabric for oblate and prolate minerals in the case of a plane deformation, on the one hand by pure shear, and on the other hand by simple shear. Theoretical and practical studies suggest a new method for determining the direction of injection (“injection axis”) in a dike, based on the angular relations of minerals near the walls.New developments are proposed on the relations between plane and linear flow-lines, on the distinction between “apparent flow-lines” and the transport-plane of the magma (“real flow-lines”) and on the amount of magma deformation.

Résumé

La mise en place d'un magma dans une caisse filonienne (ou dans des sills, dykes, laccolites, batholites, etc.) s'accompagne d'une orientation préférentielle des minéraux déjà formés. Une étude par simulation sur ordinateur a mis en évidence certains types de fabrique pour les minéraux phylliteux et les minéraux aciculaires dans le cas d'une déformation plane, d'une part par aplatissement pur et d'autre part, par cisaillement simple.En application théorique puis pratique, un nouveau critère de sens de mise en place (axe d'injection) dans une caisse filonienne est défini: le pincement des minéraux aux épontes; en effet, à chacune d'elles, les fluidalités apparentes, observées sur les minéraux, font un angle avec la paroi du filon.Des développements nouveaux sont proposés concernant les relations entre fluidalités planaire et linéaire, la distinction entre fluidalité apparente et plan de transport du magma (fluidalité réelle), le taux de déformation subi par le magma,....     

Major,minor, and trace element compositions of peridotitic and basaltic komatiites from the precambrian crust of Southern Africa

Major and trace element compositional data are reported for nine mafic and ultramafic rock samples from the Barberton greenstone belt. Rocks from this province are among the oldest fragments of the Earth's crust (3.5 b.y.). The data are consistent with an oceanic crust related origin for these rocks. The high abundances of Ni in these samples make their origin by fractional crystallization of a primitive magma unlikely but are consistent with their generation by partial melting of an upper mantle source. The basaltic samples from the Komati formation can be related by small degrees of partial melting of a primitive upper mantle source to the peridotitic komatiite which probably derived from much more extensive partial melting of a similar source. REE and especially Ni abundances limit the proportion of olivine that is permitted in the residue.     

Rare earths,other trace elements and iron in Luna 20 samples

The results of the analysis by neutron activation of six samples from the Luna 20 mission and one sample of < 1 mm fines from Apollo 16 are reported. The concentrations of the rare-earth elements (REE) in the samples of fines from Luna 20 and Apollo 16 are less than those found for corresponding materials from the mare areas but a negative Eu anomaly is still present. The concentrations of the REE in fines from Luna 20 are only about two-thirds as great as in the sample of Apollo 16 fines, but the concentrations of Co, Sc and Cr are greater by factors ranging from 1.5 to 2.3.     

The ejection of drops from the sea and their enrichment with bacteria and other materials: A review

This paper is a review of work done on the production of an aerosol by the sea, and on the mechanisms by which bacteria might be enriched on the aerosol. Air bubbles produced in the sea, primarily by breaking waves, burst at the surface to eject both film and jet drops into the atmosphere. These drops are mixed upward by turbulence to produce the well-known marine sea-salt aerosol. In rising through the water, the bubbles may scavenge bacteria which, when the bubble burst, are skimmed off the bubble and ejected upward with the jet drops. Depending on drop size, the distance the bubble moves through the water, and other factors, the concentration of bacteria in jet drops can be several hundred times that in the bulk water film drops can also be enriched with bacteria. The enrichment of jet and film drops with bacteria, viruses, or toxins may at times produce a health hazard for those living along the shore.     

Arsenic incorporation into FeS2 pyrite and its influence on dissolution: A DFT study

FeS₂ pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions.     

Correction to: Using Causal Inference in Field Development Optimization: Application to Unconventional Plays

Mathematical Geosciences - Unfortunately, in the original version of the article the first and second name of the fourth author were wrong.     

Detecting co-seismic displacements in glaciated regions: An example from the great November 2002 Denali earthquake using SPOT horizontal offsets

We use SPOT image pairs to determine horizontal offsets associated with the Mw 7.9 November 2002 Denali earthquake in the vicinity of Slate Creek, AK. Field measurements and aerial photographs are used to further characterize the geometry of the surface rupture. Aerial photographs show that shear localization occurs where the rupture trace is linear, and distributed off-fault deformation is common at fault bends and step-overs, or at geologic contacts between rock, glacial sediments, and ice. The displacement field is generated using a sub-pixel cross correlation technique between SPOT images taken before and after the earthquake. We identify the effects of glacier motion in order to isolate the tectonic displacements associated with the Denali earthquake. The resulting horizontal displacement field shows an along-strike variation in dextral shear, with a maximum of approximately 7.5 m in the east near 144° 52′W, which decreases to about 5 m to the west near 145° 45′W. If the November 2002 earthquake represents the long-term behavior of the Denali fault, it implies a westward decrease in the long-term dextral slip rate. A possible mechanism to accommodate the westward decreasing slip on the Denali fault is to transfer fault slip to adjacent east-trending contractional structures in the western region of the central Alaskan Range.     

Late Pleistocene and Holocene activity of the Atacazo–Ninahuilca Volcanic Complex (Ecuador)

The Atacazo–Ninahuilca Volcanic Complex (ANVC) is located in the Western Cordillera of Ecuador, 10 km southwest of Quito. At least six periods of Pleistocene to Holocene activity (N1 to N6) have been preserved in the geologic record as tephra fallouts and pyroclastic flow deposits. New field data, including petrographic and whole-rock geochemical analyses of over forty soil and tephra sections, 100 pumice and lithic samples, and 10 new ¹⁴C ages allow us to constrain: (1) the tephra fall isopachs and detailed characteristics of the last two events (N5–N6) including volume estimates of the tephra and pyroclastic flow deposits and the corresponding volcanic explosivity index (VEI); (2) the petrographical and geochemical correlations between domes, tephras, and pyroclastic flow deposits; and, (3) the timing of the last 4 eruptive events and a period of quiescence that endured a few thousand years (1000–4000).