Paragenese a faible variance dans les metapelites de la serie de Filali (Rif interne marocain); description, interpretation et consequence geodynamique

2001 ◽  
Vol 172 (4) ◽  
pp. 469-485 ◽  
Author(s):  
Abdelkader El Maz ◽  
Michel Guiraud
Keyword(s):  
Metamorphic Grade ◽  
Fold Axis ◽  
Metamorphic Unit ◽  
Metamorphic Series ◽  
Additional Phase

Abstract The metamorphic series of Filali and the Beni Bousera massif represent the most metamorphic unit in the inner part of the Moroccan Rif. The Filali series is composed of micaschists, gneisses, migmatites and granulites wrapped around the ultramafic body of the Beni Bousera. The foliation is broadly coherent all over the massif although differences in lineation and fold axis have been found between the granulites and the micaschists-gneisses. Metamorphic grade increases continuously towards the ultramafic body; however, seven metamorphic zones which account for this increase can be defined: - chlorite zone: muscovite and chlorite underline the S1 schistosity refolded by S2. Small garnet is wrapped by or cut across S2; - chloritoid zone: chloritoid displays the same textures as chlorite and muscovite, underlining S1 and S2 schistosity. Chlorite reacts out to biotite; - staurolite+andalusite zone: staurolite, andalusite, cordierite and garnet have pre-, syn- and post- kinematic features with respect to S2. Garnet reacts out to muscovite, biotite and plagioclase; - staurolite+andalusite+kyanite zone: same textural relationships as in the previous zone. Kyanite is an additional phase, often displaying epitaxial textures with staurolite and andalusite; - andalusite+kyanite+sillimanite zone: fibrolitic sillimanite generally associated with biotite crystallizes from staurolite. However, sillimanite is also directly formed from andalusite and kyanite. As in the previous zone garnet reacts out to biotite, muscovite and plagioclase; - sillimanite+k-feldspar zone: muscovite reacts out to k-feldspar. Modes of biotite and sillimanite increase; - migmatites zone are composed by biotite, sillimanite, garnet, cordierite quartz and feldspars. Garnets do not display the reaction textures seen in the previous zones; - granulites are composed of a primary paragenesis with kyanite+k-feldspar+garnet+ or -biotite+plagioclase+rutile, partially obliterated by a secondary paragenesis with cordierite, sillimanite and spinel.

Metamorphism of the Arseno Lake area, N.W.T., Canada: an Abukuma facies series of Aphebian age

1986 ◽  
Vol 23 (5) ◽  
pp. 646-669
Author(s):  
Peter A. Nielsen
Keyword(s):  
Northwest Territories ◽  
Electron Microprobe ◽  
Granulite Facies ◽  
Mineral Chemistry ◽  
Metamorphic Grade ◽  
Lake Area ◽  
Metamorphic Fluid ◽  
Physical Conditions ◽  
Fe Content ◽  
Metamorphic Series

Progressive mineralogical and mineral–chemical changes are described for metapelitic rocks from an Abukuma-type metamorphic series ranging from greenschist to upper amphibolite – granulite facies in the Bear Structural Province, Northwest Territories, Canada.The first appearance of the following minerals defines six isograds: biotite; andalusite; cordierite (muscovite + chlorite out); sillimanite (andalusite out); sillimanite + K-feldspar (muscovite + quartz out); and almandine + K-feldspar ± cordierite (biotite + sillimanite + quartz out).Electron microprobe analyses of the Fe–Mg silicates, biotite, cordierite, and garnet, display two distinct trends of mineral chemistry with increasing metamorphic grade. In the almandine + K-feldspar ± cordierite zone, where garnet is present, Fe/(Fe + Mg) decreases in all of the Fe–Mg silicates observed. However, in the cordierite zone and in the higher grade rocks where garnet is absent, Fe/(Fe + Mg) increases in both biotite and cordierite. Ilmenite and rutile are involved in all continuous reactions and lead to increasing Fe/Mg with grade unless garnet is a product of reaction. There is also a displacement towards lower Fe content at the sillimanite + K-feldspar isograd.The scale of equilibration decreases to 1–2 mm in the almandine + K-feldspar ± cordierite zone, which is most probably a function of the decrease of [Formula: see text] and therefore [Formula: see text]in the metamorphic fluid with increasing metamorphic grade.The physical conditions of metamorphism in the Arseno Lake area range from [Formula: see text] at 2–2.5 kbar with[Formula: see text] in the chlorite zone to ≥650 °C at 3.5–4.0 kbar where [Formula: see text] in the almandine + K-feldspar ± cordierite zone.

Object Wave Determination by Single-Sideband Methods

1973 ◽  
Vol 31 ◽  
pp. 266-267
Author(s):  
Kenneth H. Downing ◽  
Benjamin M. Siegel
Keyword(s):  
Phase Shift ◽  
Carbon Films ◽  
Object Wave ◽  
Electron Wave ◽  
Phase Object ◽  
Heavy Atoms ◽  
Single Sideband ◽  
Thin Carbon ◽  
Additional Phase Shift ◽  
Additional Phase

Under the “weak phase object” approximation, the component of the electron wave scattered by an object is phase shifted by π/2 with respect to the unscattered component. This phase shift has been confirmed for thin carbon films by many experiments dealing with image contrast and the contrast transfer theory. There is also an additional phase shift which is a function of the atomic number of the scattering atom. This shift is negligible for light atoms such as carbon, but becomes significant for heavy atoms as used for stains for biological specimens. The light elements are imaged as phase objects, while those atoms scattering with a larger phase shift may be imaged as amplitude objects. There is a great deal of interest in determining the complete object wave, i.e., both the phase and amplitude components of the electron wave leaving the object.

Characteristics of an Electrostatic Phase Plate

1972 ◽  
Vol 30 ◽  
pp. 618-619
Author(s):  
William Krakow ◽  
Benjamin Siegel
Keyword(s):  
Phase Contrast ◽  
Objective Lens ◽  
Phase Plate ◽  
Net Charge ◽  
Phase Plates ◽  
Beam Currents ◽  
Contrast Image ◽  
Bright Phase ◽  
Additional Phase Shift ◽  
Additional Phase

Unwin has used a metallized non-conducting thread in the back focal plane of the objective lens that stops out a portion of the unscattered beam, takes on a localized positive charge and thus produces an additional phase shift to give a different transfer function of the lens. Under the particular conditions Unwin used, the phase contrast image was shifted to bright phase contrast for optimum focus.We have investigated the characteristics of this type of electrostatic phase plate, both analytically and experimentally, as functions of the magnitude of charge and defocus. Phase plates have been constructed by using Wollaston wire to mount 0.25μ diameter platinum wires across apertures ranging from 50 to 200μ diameter and vapor depositing SiO and gold on the mounted wires to give them the desired charging characteristics. The net charge was varied by adjusting only the bias on the Wehnelt shield of the gun, and hence the beam currents and effective size of the source.

Friedel'S law breakdown and interpretation of stacking fault images in tetrahedral semiconductors

1987 ◽  
Vol 45 ◽  
pp. 318-319
Author(s):  
Rob. W. Glaisher ◽  
A.E.C. Spargo
Keyword(s):  
Relative Phase ◽  
Point Group ◽  
Binary Compound ◽  
Stacking Fault ◽  
Fold Axis ◽  
Atom Pair ◽  
Tetrahedral Semiconductors ◽  
Group Symmetries ◽  
Thin Crystal ◽  
Phase Differences

Images of <11> oriented crystals with diamond structure (i.e. C,Si,Ge) are dominated by white spot contrast which, depending on thickness and defocus, can correspond to either atom-pair columns or tunnel sites. Olsen and Spence have demonstrated a method for identifying the correspondence which involves the assumed structure of a stacking fault and the preservation of point-group symmetries by correctly aligned and stigmated images. For an intrinsic stacking fault, a two-fold axis lies on a row of atoms (not tunnels) and the contrast (black/white) of the atoms is that of the {111} fringe containing the two-fold axis. The breakdown of Friedel's law renders this technique unsuitable for the related, but non-centrosymmetric binary compound sphalerite materials (e.g. GaAs, InP, CdTe). Under dynamical scattering conditions, Bijvoet related reflections (e.g. (111)/(111)) rapidly acquire relative phase differences deviating markedly from thin-crystal (kinematic) values, which alter the apparent location of the symmetry elements needed to identify the defect.

THE ROLE OF SILICA IN IRON FORMATIONS: TEXTURAL, MINERALOGICAL, AND GEOCHEMICAL COMPARISONS FROM LOW METAMORPHIC GRADE NEOARCHEAN AND PALEOPROTEROZOIC EXAMPLES

2020 ◽  
Author(s):  
Latisha Ashley Brengman ◽  
◽  
Esther K. Stewart ◽  
Danielle Stolze ◽  
Emily Faust ◽  
...  
Keyword(s):  
Metamorphic Grade ◽  
Iron Formations

The empirical conformational surface of the co(ethylenediamine) ring

1990 ◽  
Vol 55 (6) ◽  
pp. 1427-1434 ◽  
Author(s):  
František Pavelčík ◽  
Eva Luptáková
Keyword(s):  
Potential Surface ◽  
Chelate Ring ◽  
Statistical Treatment ◽  
Mirror Image ◽  
Fold Axis ◽  
Empirical Potential ◽  
Reduction Of Dimensionality ◽  
Envelope Conformation ◽  
Structural Correlation ◽  
Structural Database

The conformational surface of the Co(en) chelate ring was studied by the method of structural correlation. The reduction of dimensionality of the conformation problem was achieved by employing the pseudorotation concept. The empirical potential surface was obtained by statistical treatment of 743 independent conformations from the Cambridge Structural Database. The theoretical potential surface was obtained by molecular mechanics. The minimal-energy conformation is gauche with the Co atom on the two-fold axis. Conformational flexibility also includes an envelope conformation with the N atom bent out of the plane. The transition between the mirror-image symmetrical conformations can occur by a pseudorotation pathway and is accompanied by increased planarity of the ring. The transition state is an envelope conformation with an out-plane Co atom.

scholarly journals Late oligocene–early miocene shortening in the Thrace Basin, northern Aegean

2021 ◽  
Author(s):  
Ümitcan Erbil ◽  
Aral I. Okay ◽  
Aynur Hakyemez
Keyword(s):  
Large Scale ◽  
Middle Eocene ◽  
Early Miocene ◽  
Fold Axis ◽  
Late Oligocene ◽  
The Balkans ◽  
Sedimentary Sequences ◽  
The North ◽  
Early Oligocene ◽  
Thrace Basin

AbstractLate Cenozoic was a period of large-scale extension in the Aegean. The extension is mainly recorded in the metamorphic core complexes with little data from the sedimentary sequences. The exception is the Thrace Basin in the northern Aegean, which has a continuous record of Middle Eocene to Oligocene marine sedimentation. In the Thrace Basin, the Late Oligocene–Early Miocene was characterized by north-northwest (N25°W) shortening leading to the termination of sedimentation and formation of large-scale folds. We studied the stratigraphy and structure of one of these folds, the Korudağ anticline. The Korudağ anticline has formed in the uppermost Eocene–Lower Oligocene siliciclastic turbidites with Early Oligocene (31.6 Ma zircon U–Pb age) acidic tuff beds. The turbidites are underlain by a thin sequence of Upper Eocene pelagic limestone. The Korudağ anticline is an east-northeast (N65°E) trending fault-propagation fold, 9 km wide and 22 km long and with a subhorizontal fold axis. It is asymmetric with shallowly-dipping northern and steeply-dipping southern limbs. Its geometry indicates about 1 km of shortening in a N25°W direction. The folded strata are unconformably overlain by Middle Miocene continental sandstones, which constrain the age of folding. The Korudağ anticline and other large folds in the Thrace Basin predate the inception of the North Anatolian Fault (NAF) by at least 12 myr. The Late Oligocene–Early Miocene (28–17 Ma) shortening in the Thrace Basin and elsewhere in the Balkans forms an interlude between two extensional periods, and is probably linked to changes in the subduction dynamics along the Hellenic trench.

The Relative Merits of Oxides of Hafnium, Cerium and Thorium as Surrogates for Plutonium Oxide in Calcium Phosphate Ceramics

2009 ◽  
Vol 1193 ◽  
Author(s):  
B. L. Metcalfe ◽  
S. K. Fong ◽  
L. A. Gerrard ◽  
I. W. Donald ◽  
E. S. Welch ◽  
...  
Keyword(s):  
Calcium Phosphate ◽  
Calcination Temperature ◽  
Cerium Oxide ◽  
Absorption Spectroscopy ◽  
Hafnium Oxide ◽  
Intermediate Level ◽  
X Ray Diffraction ◽  
X Ray ◽  
X Ray Absorption ◽  
Additional Phase

AbstractThe choice of surrogate for plutonium oxide for use during the initial stages of research into the immobilization of intermediate level pyrochemical wastes containing plutonium andamericium oxides in a calcium phosphate host has been investigated by powder X-ray diffraction and X-ray absorption spectroscopy. Two non-radioactive surrogates, hafnium oxide and cerium oxide, together with radioactive thorium oxide were compared. Similarities in behaviour were observed for all three surrogates when calcined at the lowest temperature, 750°C but differences became more pronounced as the calcination temperature was increased to 950°C. Although some reaction occurred between all the surrogates and the host to form a substituted whitlockite phase, increasing the temperature led to a significant increase in the cerium reaction and the formation of an additional phase, monazite. Additionally it was observed that the cerium became increasingly trivalent at higher temperatures.

scholarly journals Crystal Structure of an Aquabirnavirus Particle: Insights into Antigenic Diversity and Virulence Determinism

2009 ◽  
Vol 84 (4) ◽  
pp. 1792-1799 ◽  
Author(s):  
Fasséli Coulibaly ◽  
Christophe Chevalier ◽  
Bernard Delmas ◽  
Félix A. Rey
Keyword(s):  
Crystal Structure ◽  
Three Dimensional ◽  
Salient Feature ◽  
Infectious Pancreatic Necrosis Virus ◽  
Antigenic Determinants ◽  
Binding Motif ◽  
Icosahedral Symmetry ◽  
Fold Axis ◽  
Cell Internalization ◽  
Pancreatic Necrosis Virus

ABSTRACT Infectious pancreatic necrosis virus (IPNV), a pathogen of salmon and trout, imposes a severe toll on the aquaculture and sea farming industries. IPNV belongs to the Aquabirnavirus genus in the Birnaviridae family of bisegmented double-stranded RNA viruses. The virions are nonenveloped with a T=13l icosahedral capsid made by the coat protein VP2, the three-dimensional (3D) organization of which is known in detail for the family prototype, the infectious bursal disease virus (IBDV) of poultry. A salient feature of the birnavirus architecture is the presence of 260 trimeric spikes formed by VP2, projecting radially from the capsid. The spikes carry the principal antigenic sites as well as virulence and cell adaptation determinants. We report here the 3.4-Å resolution crystal structure of a subviral particle (SVP) of IPNV, containing 20 VP2 trimers organized with icosahedral symmetry. We show that, as expected, the SVPs have a very similar organization to the IBDV counterparts, with VP2 exhibiting the same overall 3D fold. However, the spikes are significantly different, displaying a more compact organization with tighter packing about the molecular 3-fold axis. Amino acids controlling virulence and cell culture adaptation cluster differently at the top of the spike, i.e., in a central bowl in IBDV and at the periphery in IPNV. In contrast, the spike base features an exposed groove, conserved across birnavirus genera, which contains an integrin-binding motif. Thus, in addition to revealing the viral antigenic determinants, the structure suggests that birnaviruses interact with different receptors for attachment and for cell internalization during entry.

Co-Ni-As sulphides in serpentinites of different metamorphic grade in the eastern Central Alps (Switzerland and Italy)

1989 ◽  
Vol 41 (1) ◽  
pp. 65-71 ◽  
Author(s):  
Dorothee J. M. Burkhard
Keyword(s):  
Metamorphic Grade ◽  
Central Alps
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