First Evidence of the Post-Variscan Magmatic Pulse on the Western Edge of East European Craton: U-Pb Geochronology and Geochemistry of the Dolerite in the Lublin Podlasie Basin, Eastern Poland

Ewa Krzemińska,Jolanta Pacześna,Leszek Krzemiński,Paweł Poprawa,Krzysztof Nejbert

doi:10.3390/min11121361

Ewa Krzemińska, Jolanta Pacześna + Show 3 more

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https://doi.org/10.3390/min11121361

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Abstract

The U–Pb measurements of youngest, coherent group of zircons from the Mielnik IG1 dolerite at the Teisseyre-Tornquist margin (TTZ) of East European Craton (EEC) in Poland yielded age of 300 ± 4 Ma. Zircon dated an evolved portion of magma at the late stage crystallization. It is shown that this isolated dyke from the northern margin of the Lublin Podlasie basin (Podlasie Depression) and regional dyke swarms of close ages from the Swedish Scania, Bornholm and Rügen islands, Oslo rift, Norway, and the Great Whine Sill in northeastern England, were coeval. They have been controlled by the same prominent tectonic event. The Mielnik IG1 dolerite is mafic rock with Mg-number between 52 and 50 composed of the clinopyroxene, olivine-pseudomorph, plagioclase, titanite, magnetite mineral assemblage, indicating relatively evolved melt. This hypabyssal rock has been affected by postmagmatic alteration. The subalkaline basalt composition, enrichment in incompatible trace elements, progressive crustal contamination, including abundance of zircon xenocrysts determines individual characteristics of the Mielnik IG1 dolerite. The revised age of dolerite, emplaced in vicinity of TTZ provides more evidences documenting the reach of the Permo-Carboniferous extension and rifting accompanied by magmatic pulses, that were widespread across Europe including the margin of the EEC incorporated that time into the broad foreland of the Variscan orogen.

Highlights

The south-western part of East European Craton (EEC), after the collision of three protocratons: Volgo-Uralia, Sarmatia and Fennoscandia, had been completed at ca. 1.82–1.80 Ga [1]and has become a relatively stable continental region
The morphology of crystals picked from the Mielnik IG1 dolerite, from a depth of 1745 m (Figure 5) suggests a dominance of inherited or xenocrystal forms, several small and sharply faceted, prismatic crystals, indicated a primary igneous origin
More than half (58%) of the zircons provide significantly older ages than the rest of the analyzed grains e.g., Paleoproterozoic to Late Ediacaran

Summary

Introduction

The south-western part of East European Craton (EEC), after the collision of three protocratons: Volgo-Uralia, Sarmatia and Fennoscandia, had been completed at ca. 1.82–1.80 Ga [1]and has become a relatively stable continental region. Its cratonised structure has been complicated by faults, rift zones. Their distribution provides information about the spatial and temporal changes of ancient crustal structures, the regional stress field, their intensity and reasons for them. They became pathways for the injections of melts, forming a single dyke or swarms of dykes. The crystalline basement of Fennoscandia and its sedimentary cover was pierced by a few generations of dykes. At ca 1.27 Ga mafic sills and dykes in the central part of Scandinavia, represented by the Västerbotten, Ulvö, Jämtland, Satakunta and Dalarna “post-Jotnian” dolerite, intruded in response to the rifting of Laurentia/Baltica [2,3]

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