A staining method for distinguishing paragonite from muscovite in thin section

Sodium cobaltinitrite can be used to stain muscovite, to distinguish it from paragonite. The stain is inhibited in the neighbourhood of feldspar crystals

Cleavage-fold relationships in the lower Cambrian Tubize group, southeast Anglo-Brabant fold belt (Lembeek, Belgium)

Little is known about the cleavage-fold relationships in the Lower Palaeozoic Brabant Massif, primarily because of the scarcity of suitable exposures. Moreover, to date, folds have only been described in the Ordovician and Silurian sequences along the southern extremity of the basement. However, excavation works for the construction of the TGV(railway)-track south of Brussels created an opportunity to study cleavage-fold relationships in the Lower Cambrian terrigenous series (Tubize Group) in a more central part of the Brabant Massif. The structural features observed seemed inconsistent with the suspected regional trends. Primarily, a divergent cleavage fan was observed in a region thought to have a regular cleavage attitude. The symmetrical but divergent disposition of the cleavage with regard to the fold hinges is explained by flexural folding of a pre-existing bedding-parallel compaction fabric. Cleavage development and folding are considered synchronous. The divergent cleavage fan reflects local strain variations. Also the steeply plunging hinge lines of the open, subangular folds are seemingly inconsistent with the regional trend characterized by subhorizontal fold hinges. Taking into account the structural position of the fold assemblage in the subvertical limb of a large-scale, upright, isoclinal fold structure, the fold assemblage is interpreted as an incongruous parasitic feature. The steeply plunging hinge Lines are considered to be caused by fold hinge rotation during progressive coaxial deformation. Although this incongruous fold assemblage with its divergent cleavage fan is localized, it provides important information on both local and regional deformation circumstances in this part of the Anglo-Brabant Fold Belt

Réflectance et composition chimique du gîte sédimentaire de Chaudfontaine et du gîte filonien de la Rochette (Province de Liège, Belgique)

The morphological, optical and chemical features of bravoites from a sedimentary ore deposit at Chaudfontaine and a vein-type ore deposit at La Rochette, both in Belgium, are compared. In addition to a zonal structure, a spotted structure has been observed in the cores of some crystals. The correlation between reflectance and Ni content is confirmed only for Co-poor bravoites.-R.A.H.info:eu-repo/semantics/publishe

Réflectance et composition chimique des bravoïtes du gîte sédimentaire de Chaudfontaine et du gîte filonien de La Rochette (Province de Liège, Belgique)

This paper deals with the study of the morphological, optical and chemical features of bravoites from a sedimentary ore deposit (Chaudfontaine) and a vein-type ore deposit (La Rochette). In both cases, the reflectance and the chemical composition have been compared. Besides a zoned structure, a spotted structure has been observed in the core of some crystals. Furthermore, the correlation between reflectance and Ni-content has been confirmed only for Co-poor bravoites.Cette note concerne l'étude des caractères morphologiques, optiques et chimiques de bravoïtes provenant de gisements de deux types différents : l'un sédimentaire (Chaudfontaine) et l'autre filonien (La Rochette). Réflectance et composition chimique ont été comparées dans les deux cas. A côté d'une structure zonée classique, une structure tachetée localisée dans la partie centrale de certains cristaux a été mise en évidence. En outre, la corrélation réflectance-teneur en Ni n'a été confirmée que pour des bravoïtes très pauvres en Co.Dejonghe Léon, Wautier Jacques, Laduron Dominique. Réflectance et composition chimique des bravoïtes du gîte sédimentaire de Chaudfontaine et du gîte filonien de La Rochette (Province de Liège, Belgique). In: Bulletin de Minéralogie, volume 108, 5, 1985. pp. 679-690

Petrology and geodynamic significance of the post-collisional Pan-African magmatism in the Eastern Saghro area (Anti-Atlas, Morocco)

The Saghro Group consists of a thick volcanic-sedimentary sequence with intercalated basaltic lavas, the first magmatic event in eastern Saghro area. Nd isotopes of basaltic pillow lavas show T-DM model ages ranging from 640 to 580 Ma, which represent a maximum age for basalt eruption. Granitoids within the Saghro Group consist of a charnockitic suite, tonalites, granodiorites and monzogranites. They are high-K calc-alkaline (HKCA) with a post-collisional character, and were emplaced at high-levels in the crust. Their ages of emplacement are within the 580-560 Ma bracket, implying that the entire Saghro Group is slightly older than or partly coeval to granitoid emplacement and implying a common geodynamical setting. Sr-Nd isotopic compositions and Nd T-DM model ages point to a mixed origin, combining a juvenile mantle source and an Eburnean crustal component, which could be the West African Craton (WAC). The juvenile component in the Saghro granitoids could be the depleted upper mantle that has sourced the earlier basalts. Field observations, geochemical and geochronological data together support that, during the Pan-African orogeny, the Anti-Atlas was subjected to a regional transpressional to transtensional event. This event would have been responsible for the dissection of the northern margin of the WAC into several blocks, the development of deep sedimentary basins and the emplacement of HKCA magmas. (C) 2009 Elsevier Ltd. All rights reserved