Magnetofabric and textural analysis from highly anisotropic magnetite bearing shear zones in metamorphic nappes of the Scandinavian Caledonides
Final Report Abstract
Magnetite-bearing mylonitic garnet micaschists close to the major suture between the Baltica and Iapetus terranes (Seve Nappe Complex, Scandinavian Caledonides) show very high anisotropy of magnetic susceptibility (AMS) with corrected degree of anisotropy (P’) of up to 4.8. Three different magnetic fabric types can be distinguished. They correspond to protomylonite (type I, P’ < 2), mylonite (type II, 2 < P’ < 3), and ultramylonite (type III, P’ > 3), respectively. The orientation of the ellipsoid axes from all applied magnetic fabric methods in this study is similar with shallow dips of the metamorphic foliation towards WSW and subhorizontal, mostly NW-SE trending mineral lineation. Differences between subfabrics were minimized under high shear strain as all markers tend to align parallel with the shear plane. The very high anisotropies and mostly oblate ellipsoid shapes of type III correlate with high magnetic susceptibility (kmean up to 55 x 10-3 SI units) and are related to the concentration of magnetite aggregates with shape-preferred orientation. They show a distinct field dependence of magnetic susceptibility of up to 10% in the kmax-direction. We attribute this field dependence to a “memory” of high strains in the domain walls of the crystals acquired during synkinematic magnetite growth during shear zone fabric development at temperatures of 550 to 650°C.
Publications
- (2006). Very high anisotropies of the magnetic susceptibility in ductile shear zones: first quantitative results from a metamorphic nappe in the Central Scandinavian Caledonides, Sweden. 11. Symposium Tektonik, Struktur- und Kristallingeologie, Göttingen: 72-73
Grimmer, J.C.
- (2009). Magnetofabric and textural analysis from highly anisotropic magnetite-bearing mylonitic garnet micaschist of the Scandinavian Caledonides. Annual report BGI, 147-149
Engelmann, R., Kontny, A., Grimmer, J., Heidelbach, F.
- (2009). Very high anisotropies of magnetic susceptibility in a shear zone from the Scandinavian Caledonides: a magnetofabric and textural analysis. Geophysical Research Abstracts, 11, EGU2009-7763
Engelmann, R., Grimmer, J., Kontny, A., Hirt, A.M., Greiling, R.O.
- (2010). High magnetic anisotropies in magnetite-bearing mylonitic garnet-micaschist of the Seve nappe, Swedish Caledonides. American Geophysical Union, Fall Meeting 2010
Kontny, A. M., Grimmer, J., Engelmann, R., Greiling, R. O.
- (2010). Magnetofabric analysis from highly anisotropic magnetite-bearing mylonitic garnet micaschist of the Scandinavian Caledonides. 13. Symposium Tektonik, Struktur- und Kristallingeologie Frankfurt
Grimmer, J.C., Engelmann, R., Kontny, A., Greiling, R.O.
- (2011). Process of magnetite fabric development during granite deformation. Earth and Planetary Science Letters, 308, 77-89
Mamtani, M.A., Piazolo, S., Greiling, R.O., Kontny, A., Hrouda, F.
(See online at https://doi.org/10.1016/j.epsl.2011.05.033) - (2012). A Silurian top-to- NW ductile shear zone in the Seve Nappe Complex (central Scandinavian Caledonides, Sweden): The top of a Scandian palaeo-extrusion wedge? 14. Symposium Tektonik, Struktur- und Kristallingeologie Kiel: 43
Grimmer, J.C., Glodny, J., Drüppel, K., Kontny, A., Greiling, R.O.
- (2012). Magnetofabric analysis from highly anisotopic magnetite-bearing mylonitic garnet-micaschists in a metamorphic nappe (Seve Nappe Complex, Scandinavian Caledonides). International Journal of Earth Sciences (Geol. Rundsch) 101: 671-692
Kontny, A., Engelmann, R., Grimmer, J., Greiling, R.O., Hirt, A.
(See online at https://doi.org/10.1007/s00531-011-0713-8)
