Magma generation in an alternating transtensional–transpressional regime, the Kraków–Lubliniec Fault Zone, Poland

In the Kraków–Lubliniec Fault Zone (KLFZ) late Carbonifereous–Permian volcanic rocks mark the boundary between the Małopolska Block (thinned marginal sector of Baltica) and the Upper Silesian Block (a sector of the Brunovistulia composite Terrane). The Zone is a part of the major Hamburg–Kraków–Dobrogea transcontinental strike–slip tectonic zone separating the Laurussian craton and Gondwana blocks which came together to form it. The geochemistry of the volcanic rocks reflects the collisional nature of the tectonism. However, it also presents a signature compatible with extensional magmatism. The paper presents models of magma generation and evolution in what was a zone of alternating transpression and transtension. The magmatism in this zone of amalgamated terranes was related to two different sources: enriched mantle and primitive crust. The lithospheric mantle beneath some blocks of the amalgamated terranes may have experienced enrichment processes during previous subduction events. The metasomatism may have also occurred as a result of crustal thickening during transpression followed by delamination, subsidence and melting. These metasomatised blocks reacted with decompressional melting. Our results show that magma generation and evolution in the zone seem to be not typical examples of late Carbonifereous–Permian magmatism, which is known from other locations throughout Central Europe. ►Complex melting process in transcontinental strike–slip tectonic zone. ►Mantle metasomatism occurring due crustal thickening during transpression followed by delamination and melting. ►KLFZ (Kraków–Lubliniec Fault Zone) — not typical examples of late Carbonifereous–Permian magmatism.