Etude du comportement, au cours de l'altération météorique, de plagioclases de type labrador en comparant deux altérites formées aux dépens d'une pyroxénite crétacé du Mont Saint-Bruno (Québec) et d'une basanite pliocène du Massif Central français.
Pseudomorphic transformation of plagioclases during the weathering of granitic rocks in Galicia (NW Spain)
Microscopic study of twelve weathering profiles developed on granitic rocks in Galicia (NW Spain) showed that, in most cases, the transformation of the parent rock into saprolite occurs with pseudomorphic alteration of the plagioclases
Differential roles of plagioclase and biotite in the early stage weathering of granite : a solid-sided approach combining laboratory experiment and surface analysis
, plagioclase played the background role in near-neutral to acidic conditions. The increase of pH level due to plagioclase dissolution promoted Fe-oxide precipitation from biotite. Moreover, the precipitation of products including Al started slower, mainly
Examination of weathering rinds from lava flows on Hawaii with backscatter electron microscopy and electron microprobe analysis reveals that olivine weathers more slowly than adjacent clinopyroxene and plagioclase in environments with a paucity
of organic acids. Yet when wheathering rinds are in contact with abundant organic acids secreted by lichens, olivine weathers before clinopyroxene and plagioclase weathers last. This illustrates the importance of the biogeochemical environment.
Etude théorique de l'altération des plagioclases. Bilans et conditions de stabilité des minéraux secondaires en fonction de la pression partielle de CO et de la température (0C à 100C)
Les itinéraires chimiques de l'altération des plagioclases sont calculés en considérant les relations thermodynamiques d'équilibre entre minéraux et solutions, ceci en système ouvert| cette situation est analogue à celle d'un volume d'eau suivant un
The possible impact of periglacial climates on the rate of chemical weathering of a coarse-grained plagioclase-muscovite-quartz schist has been determined for a small watershed near Baltimore, Maryland. The results suggested by the chemical
the second weathering stage plagioclase is altered into kaolinite, and the breakdown of dark minerals promotes leaching of Ca, Na, Fe and Mg. The residue has been slightly enriched in K-feldspar, quartz and clay minerals. Si and Al have not dissolved during
by SEM before and after the experiment. B. subtilis had a strong influence on granite weathering by forming pits. Plagioclase was more vulnerable to bacterial weathering than biotite among the granite composing minerals.
. The relative contents of K-feldspars and plagioclase vary markedly in the different zones. The pH of the dust is significantly higher than that of the local soils, indicating that a substantial amount of the dust comes from the Sahara.
à l'altération maximale des plagioclases en argile et consiste en une succession de microdécrochements induisant la formation de lits de structure et granulométrie différentes. (BH).
L'étude détaillée des coupes et l'examen aux microscopes optique et électronique ainsi que l'analyse à la microsonde montrent que la naissance du fauchage correspond à l'altération maximale des plagioclases en argile, ce qui prépare les
: amphibole gives way to smectites (saponites and montmorillonites) and plagioclase produces montmorillonites followed by kaolinite/smectite mixed layers and kaolinite. Second, each clay mineral, with its specific sorption capacity, appears to control
the distribution of the heavy metals within the soil : the smectites produced by the amphiboles have high sorption capacity and favor the retention of the metals in the upper horizons of the soil; the kaolinites produced by the plagioclases have low sorption
trouvée dans les tills sous-jacents, tandis que le quartz et le plagioclase apparaissent en plus faibles quantités. Ces propriétés reflètent une altération météorique sous un climat semi-aride ainsi que la présence de matériaux déjà altérés dérivant de
by clay-sized plagioclase, K-feldspar, and biotite in homogeneous internal composition. The abundance of rock flour is deemed proportional to the intensity of glacier advances.
Elena materials are more intensely weathered. High fracturation and high Ca-richer plagioclase contents are key factors producing the pervasive Santa Elena stock weathering. Fluvial erosion removed the alteration products in incised tectonically
coast sourced by a wide variety of paleozoic terranes. This study demonstrates how the presence of plagioclase grains with magnetic inclusions is a good indicator of river control in a coastal area and how the content of monomineralic opaque grains might
massives couvertes de grosses boules. Si la taille des minéraux n'est pas toujours significative, il semble en revanche que le pourcentage et la forme des interstices entre les plagioclases, ainsi que l'orientation de la structure expliquent l'intensité