Magnetic fabrics in garnet peridotites–pyroxenites and host felsic granulites in the South Bohemian Granulites (Czech Republic): Implications for distinguishing between primary and metamorphism induced fabrics

Abstract

In the high-grade Moldanubian Zone of the European Variscides, numerous bodies of ultramafic rocks occur embedded in granulite. The anisotropy of magnetic susceptibility and its low-field variation as well as the anisotropy of magnetic remanence were used to investigate magnetic fabrics of some ultramafic bodies and host granulite. In granulite, the magnetic foliation is roughly parallel to the metamorphic foliation and the magnetic lineation is near the mineral alignment lineation. In ultramafite, the magnetic foliation is relatively scattered spatially, but mostly oriented in a different way than that in granulite. The magnetic lineation is also scattered, but still relatively well defined spatially. Again, its orientation is mostly different than that of granulite. The magnetic fabric in ultramafic rocks is therefore different from that in the host granulite even though both rock types underwent at least partially common structural history. The componental movements forming the granulite fabric, mostly during amphibolite facies retrograde metamorphism, were evidently not intensive enough to strongly overprint the magnetic fabric of ultramafite. The ultramafite is therefore strong enough to maintain its pre-metamorphism fabric even at such high temperatures and pressures that are characteristic of high amphibolite facies retrograde metamorphism.