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Evidence of magmatic versus hydrothermal zircon ages and mantle-crust interactions obtained from the Carboniferous alkaline intrusions at the margin of East European Craton (NE Poland)

par Krzemińska, Ewa;Krzemiński, Leszek;Demaiffe, Daniel ;Poprawa, Paweł;Williams, Ian I.S.;Wiszniewska, Janina
Référence Gondwana research, 142, page (44-72)
Publication A Paraître, 2025-07-01

Article révisé par les pairs

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Résumé :

The Mazury Alkaline Intrusions (MAI), consisting of both silica-oversaturated and undersaturated rocks, are situated at the tectonically weakened western margin of the East European Craton (EEC). SHRIMP zircon U-Pb dating of nine syenitic samples, combined with zircon δ18O oxygen isotope data and mineral chemistry, provides insight into the Carboniferous magmatic-to-hydrothermal evolution of the MAI. Three magmatic pulses, at 352 ± 3 Ma, 344 ± 3 Ma and 337 ± 2 Ma, have been recognized. Each was followed closely by hydrothermal activity, dated at 351 ± 3 Ma, 347 ± 5 Ma and 333 ± 12 Ma, respectively. The hydrothermal stages were identified from hydrothermal zircon in the silica undersaturated syenites; its porous texture, its high abundance of non-formula elements (LREE, Y, Th, U) and its depletion in 18O, in some cases resulting in negative δ18O values. The zircon with higher δ18O values in the silica oversaturated syenites reflects crystallization from crustal melt, consistent with negative whole rock εNd(t) values ranging from −3.19 to −5.02, indicative of melts generated in the lower crust. Positive whole-rock εNd(t) values, from + 2.34 to + 0.86, obtained from undersaturated nepheline syenites indicate a depleted mantle source. TDM model ages calculated for rocks from the MAI, and from the Devonian Kola province and Permian Oslo rift, reveal a similar interval of 0.74–0.62 Ga, pointing to common geodynamic processes having affected the EEC margins during the Neoproterozoic break-up of Rodinia. The intraplate MAI differs from the typical late Paleozoic rift-related alkaline provinces of the EEC. The newly identified phases of the MAI magmatism coincide in time with the Variscan continent/continent collision. This might have led to transmission of lithospheric-scale tectonic stress into the far foreland of the orogen, including the western EEC, and possibly also to the strike-slip reactivation of pre-existing tectonic zones, resulting in local mantle decompression.