The ca. 1.8 Ga mantle plume related magmatism of the central part of the Ukrainian shield

Abstract

International audiencePalaeoproterozoic (ca. 1.8 Ga) mafic and ultramafic dykes are widely distributed within the whole Sarmatian segment of the East-European craton. This paper focuses on new geochronological, geochemical and isotope data obtained for mafic and ultramafic dykes of the Ingul terrain. Geochronological data available for these dykes indicate ages around 1800 Ma. We provide a new U–Pb zircon age of 1810 ± 15 Ma obtained for a dolerite dyke in the Kirovograd area. Geochemical and petrographical data allow identification of three groups of dykes: (1) kimberlites, (2) high-Mg# subalkaline rocks (picrite, camptonite, subalkaline dolerite etc.) and (3) tholeiite dolerite. Rocks of these groups were probably derived from different sources. εNd1800 values of studied rocks vary from 0.7 to 2.8. The highest values were obtained for mantle xenoliths and their kimberlite host (εNd1800 = 2.5–2.8). Rb–Sr data yield a regression age of 1729 ± 20 Ma with an initial 87Sr/86Sr = 0.70366 ± 41 (MSWD = 10.8). The whole-rock lead isotope data scatter, but data for sub-groups of samples can tentatively be fitted to parallel 1.8 Ga isochrons. The geochemical data indicate rocks to have formed by partial melting and the degree of melting is thought to be a function of formation depth, the latter ranging from sub-lithospheric to lower-crustal levels; we assume that melting was caused by a mantle plume. Dyking in the Ingul terrain was closely associated in time and space with metasomatic albitites that host numerous economic U deposits

The origin of the Palaeoproterozoic AMCG complexes in the Ukrainian shield: New U-Pb ages and Hf isotopes in zircon

“…Sparse geochronological data available for the dykes indicate emplacement at c. 1800 Ma. The possible relation of these mantle-derived dykes to a mantle plume, or to delamination of lithosphere caused by collision of Sarmatian and Fennoscandian segments of the East-European platform shortly before 1800 Ma, was discussed in details by Shumlyanskyy et al (2016b). The intra-plate nature of this magmatism remains beyond doubt.…”

“…Most of these dykes were intruded between 1770 and 1790 Ma (Chernyshov et al, 2001;Bogdanova et al, 2013;Shumlyanskyy et al, 2012;2016b) which is perhaps longer than might be expected in many models of magmatism linked to the emplacement of a mantle plume.…”

“…The temporal relationships between the main rock types had not been established, and correlation between the two Ukrainian AMCG complexes was hampered by the lack of data from one of them. Finally, it had been shown recently that mantle-derived dykes that vary in composition from kimberlite to tholeiitic dolerite, and which are widely distributed in the Ukrainian shield, are coeval with the AMCG complexes (Shumlyanskyy et al, 2012;2016a;2016b;Bogdanova et al, 2013).…”

U-Pb Age and Hf Isotope Systematics of Zircon from Eclogite Xenoliths in Devonian Kimberlites: Preliminary Data on the Archaean Roots in the Junction Zone between the Sarmatian and Fennoscandian Segments of the East European Platform

“…In the Ukrainian Shield, mantle xenoliths occur in the Palaeoproterozoic and Devonian kimberlites [17][18][19], whereas eclogite xenoliths have been described only in kimberlite fragments found in the late Palaeozoic breccias within the Prypyat horst [18]. In this short communication, we reported results of U-Pb dating and Hf isotope studies of two rare zircon crystals that were extracted from small eclogite xenoliths.…”

The mantle source of fluids for the U-bearing Na-metasomatites of the central-ukrainian uranium province inferred from Pb, Sr and Nd isotope composition

“…Деякі з цих дайок дещо давніші за метасоматити і зазнають впливу метасоматичних розчинів, тоді як молодші дайки січуть метасоматичні тіла [7,10,11]. Наявні геохронологічні дані вказують на те, що вкорінення дайок відбувалось майже 1800 млн років тому [36]. Такий самий вік мають і Na-метасоматити [4,23].…”