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Titre : | Étude géologique et géophysique du granite bleu de Lanhélin du site de La Chauffetière (Ille-et-Vilaine, 35) |
Auteurs : | Rémi CHAMPIGNY ; Ewen DENNIELOU |
Type de document : | Mémoire d'initiation à la recherche |
Année de publication : | 2021 |
Concepts : |
GRANODIORITE
MAGNETOMETRE FRACTURATION |
Résumé : | Lanhélin is located in Ille-et-Vilaine (35). It is a small village known above all for the bluish-coloured granite extracted from its quarries. This region is still poorly known from a geological point of view and precise mapping of the Lanhélin region has never been done due to the few outcrops. The objective of this study is to characterize the blue granite, its alteration and to understand its structure and the organization of its faults to facilitate the exploitation of the granite from the La Chauffetière site. To this end, technical means have been put in place, such as electric tomography and magnetometer. These studies were also associated with a systematic inventory of visible fractures on the mine faces as well as the taking of samples for macroscopic and thin-sheet analysis of the granite and its various alterations. The tectonic study reveals two fracturing directions at the La Chauffetière site. The first is N95-80N, i.e. East-West, and the second is N20-85SE, i.e. almost North-South. Three hypotheses for the main stress directions were proposed, considering the two ferromagnesian sills visible at this site and at Bécanne. The petrographic analysis of the samples shows the homogeneity of the facies within the mining pit, i.e. a leucocratic granodiorite with a bluish tint and a monzogranitic tendency. The alteration profile of the granodiorite was revealed by the electrical tomography method. This method seems to have an interesting potential for rock quality prospecting on site. |
Spécialité : | Géologie |
Numéro de promo : | 83 |
numéro MIR : | 906 |