Petrogenesis of orogenic lamproites of the Bohemian Massif: Sr-Nd-Pb-Li isotope constraints for Variscan enrichment of ultra-depleted mantle domains

0460319 - GLÚ 2017 RIV NL eng J - Článek v odborném periodiku
Krmíček, Lukáš - Romer, R. L. - Ulrych, Jaromír - Glodny, J. - Prelevič, D.
Petrogenesis of orogenic lamproites of the Bohemian Massif: Sr-Nd-Pb-Li isotope constraints for Variscan enrichment of ultra-depleted mantle domains.
Gondwana Research. Roč. 35, 1 July (2016), s. 198-216. ISSN 1342-937X. E-ISSN 1878-0571
Institucionální podpora: RVO:67985831
Klíčová slova: Silica-rich lamproites * Sr-Nb-Pb-Li isotopes * mantle metasomatism * Variscides
Kód oboru RIV: DB - Geologie a mineralogie
Impakt faktor: 6.959, rok: 2016

During convergence of Gondwana-derived microplates and Laurussia in the Palaeozoic, subduction of oceanic and continental crusts and their sedimentary cover introduced material of regionally contrasting chemical and isotopic compositions into the mantle. This slab material metasomatised the local mantle, producing a highly heterogeneous lithospheric mantle beneath the European Variscides. The eastern termination of the European Variscides (Moldanubian and Saxo-Thuringian zones of Austria, Czech Republic, Germany and Poland) is unusual in that the mantle was modified by material from several subduction zones within a small area. Orogenic lamproites sampled this lithospheric mantle, which has a chemical signature reflecting extreme depletion (low CaO and Al.sub2O₃ contents and high Mg-number) followed by strong metasomatic enrichment, giving rise to crust-like trace element patterns, variable radiogenic ⁸⁷Sr/⁸⁶Sr(330) (0.7062-0.7127) and non-radiogenic Nd isotopic compositions (εNd(330) = -2.8 to -7.8), crustal Pb isotopic compositions, and a wide range of δ⁷Li values (-5.1 to +5.1). This metasomatic signature is variably expressed in the lamproites, depending on the extent of melting and the nature of the source of the metasomatic component. Preferential melting of the metasomatically enriched (veined) lithospheric mantle with K-rich amphibole resulted in lamproitic melts with very negative, crust-like δ⁷Li values, which correlate positively with peralkalinity, HFSE contents and lower εNd. Both the higher degree of melting and progressive consumption of the metasomatic component reduce the chemical and isotopic imprints of the metasomatic end member. The very positive δ⁷Li values of some lamproites indicate that the source of these lamproites may have been modified by subducted oceanic lithosphere.

Trvalý link: http://hdl.handle.net/11104/0260430