Magnetite grain shape fabric and distribution anisotropy vs rock magnetic fabric: a three-dimensional case study

Asymmetrical to symmetrical magnetic fabric of dikes: Paleo-flow orientations and Paleo-stresses recorded on feeder-bodies from the Motru Dike Swarm (Romania)

“…Anisotropy of magnetic susceptibility in rocks dominated by amphibole and magnetite in various amounts and sizes (and locally by iron sulfide and/or hematite) results mainly from the shape-preferred orientation of these grains, even if possible interactions between magnetite organized in clusters of grains describing a distribution anisotropy only play a minor role (Hargraves et al, 1991). In the studied dikes, due to the relatively lower susceptibility and the probable magmatic origin, the distribution of grains of magnetite in space is more distant than their diameter (Grégoire et al, 1998). Thus, magnetic interaction is highly unlikely, and the origin of magnetic anisotropy appears to be mainly controlled by the individual anisotropy of each grain.…”

“…Magnetic fabric, i.e. SPO of magnetic mineralogy (except in the case of rare, possibly magnetite, interactions when crystals of a sufficient amount in lava are organized along oblique clusters; Grégoire et al, 1998;Cañón-Tapia, 2001), has also been investigated in numerous cases and appears to be a good subfabric of the real magmatic fabric (bulk shape preferred orientation of crystals in a magmatic medium). Nevertheless, the assumption that the principal magnetic vector, K 1 , represents the flow direction everywhere through a dike is not always verified (Rochette et al, 1999;Callot et al, 2001;Geoffroy et al, 2002) but the flow could be approached by the local or mean orientation of imbricate foliations along the dike's walls.…”

Hydrothermally-induced changes in mineralogy and magnetic properties of oxidized A-type granites

“…These values are among the highest values encountered in ferromagnetic plutonic rocks (see Bouchez, 2000, for comparison). In these syntectonically emplaced magmas, Grégoire et al (1998) established that such values reflect high shape ratios of primary magnetite grains. By contrast, the Meruoca and Bushveld granites display low anisotropy degrees, consistent with their emplacement as nearly undeformed shallow intrusions.…”

Determination of Rock Cleavages Using AMS (Anisotropy of Magnetic Susceptibility): a Case Study on the Geochang Granite Stone, Korea

“…앞서 '대자율이방성의 연구원리' 에서 기술한 바와 같이, 이러한 경우 k 3 축은 광물결 정들의 편평면(flattening plane)에 수직하며, k 1 축은 광물결정들의 평균 장축방향에 각각 평행하게 된다 (eg. Borradaile, 1988;Taring and Hrouda, 1993;Bouchez, 1997;Grégoire et al, 1998). 연구가 수 행된 6개 석산 모두에서 미세구조의 모양은 편평형 또는 3축형으로 나타나며 세 주축들 중 k 3 가 매우 양 호한 군집도를 보인다.…”