Magnetic fabric in amphibolized eclogites and serpentinized ultramafites in the Mariánské Lázně Complex (Bohemian Massif, Czech Republic): Product of exhumation-driven retrogression?

摘要

The largest body of metabasic rocks in the BohemianMassif, theMariánské Lázně Complex (MLC), represents an Early Paleozoic ophiolite complex, which experienced poly-metamorphic evolution with an early high-pressure amphibolite, followed by eclogite and subsequent amphibolite facies overprint. This study aims to investigate the fabric relationships among the rock bodies and to analyze the deformation-recrystallization history of the MLC using the anisotropy of magnetic susceptibility (AMS). Magnetic susceptibility of theMLC rocks varies according to the presence of para- and ferromagnetic minerals as well as according to the primary lithologies. In weakly magnetic rocks (K_m < 1 × 10~(-3) [SI]), the main carrier of susceptibility is paramagnetic mafic silicates, amphibole and biotite in amphibolites, clinopyroxene and garnet in eclogites, olivine and serpentine minerals in serpentinized ultramafite, and amphibole in gabbro. In highly magnetic rocks (K_m?1 × 10~(-3)), ferromagnetic minerals, such as magnetite, titanomagnetite, general Fe-Ti oxides, and subordinately also pyrrhotite can play an important role. The results of AMS indicate that the orientation ofmagneticminerals inmost rocks is related to the last exhumation and retrogression event that occurred in amphibolite facies conditions. However, there are some well preserved eclogites possessing themagnetic fabrics that are at least partially related to prograde or peak PT conditions during metamorphism. In addition, massive metagabbros that suffered only weak deformation partially preserve the intrusive magnetic fabrics.