Magnetic fabric and emplacement of dykes of lamprophyres and related rocks of the Central Bohemian Dyke Swarm (Central European Variscides)

Abstract

Numerous dykes of lamprophyres and various types of granitoid, syenitoid, dioritoid, and gabbroid porphyries of Variscan age crop out in the area of the Central Bohemian Plutonic Complex and adjacent high- to low-grade metamorphic units of the Moldanubian Zone and Teplá-Barrandian Unit. Magnetic fabric in fourteen dykes of lamprophyres and related rocks was investigated. Mostly, the magnetic foliation is roughly parallel to the dyke plane and the magnetic lineation is horizontal with the relics of originally steep fabrics. This type of magnetic fabric originated through magma flow in which the larger surfaces of the magnetic minerals were oriented parallel to the dyke plane and their longer dimensions were parallel to the magma flow. In two localities, the so-called inverse fabrics were found in which the maximum and minimum susceptibility directions were swapped. The dykes of lamprophyres and related rocks were emplaced into already juxtaposed and cooled Teplá–Barrandian Zone, Central Bohemian Plutonic Complex and western Moldanubian Zone not later than 339 Ma. Parallel orientation of dykes giving a steep intrusive contacts mainly in W(NW)–E(SE) trend was caused by the regional stress field of ~WNW–ESE convergence (arc-parallel stretching) during the Variscan Orogeny.