Magmatic evolution of compositionally heterogeneous monogenetic Cenozoic Strzelin Volcanic Field (Fore-Sudetic Block, SW Poland)

Erosional remnants of the Miocene Strzelin Volcanic Field in SW Poland were studied in terms of volcanology, petrology and Sr-Nd-Pb isotope geochemistry with the aim to identify the reasons for compositional variability of monogenetic volcanoes. The obtained data suggest that a heterogeneous mantle peridotite (with mixed DM/ HIMU signature) was the dominant source of magmas. Partial melting and segregation of magmas in diapirically rising asthenosphere occurred within the garnet stability field. The source heterogeneity was the basic cause that controlled the compositional variability of the primary magmas, and also influenced the subsequent differentiation processes and eruptive styles. On the surface, additional role was played by variable environments (i. e. phreatomagmatic eruptions in water-saturated environments). More fertile mantle domains, with prevailing HIMU component, released melts deeper, at lower degrees of partial melting and small magma batches were formed. These nephelinitic magmas underwent only limited fractional crystallization en route to the surface and erupted with low explosivity as lava flows. In contrast, less fertile mantle domains, dominated by the DM component, released melts at higher degrees of partial melting at a shallower depth. This resulted in a more sustained magma supply that further enhanced the development of shallow-level magmatic systems, with more advanced and complex differentiation: larger degrees of fractional crystallization as well as replenishment by new batches of primitive magma. The resulting basaltic and trachybasaltic volcanoes showed a greater diversity of eruptive styles, including effusive and variably explosive eruptions.