Publication detail

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

KRMÍČEK, L. ROMER, R. L. ULRYCH, J. GLODNY, J. PRELEVIĆ, D.

Original Title

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

Type

journal article in Web of Science

Language

English

Original Abstract

During convergence of Gondwana-derived microplates and Laurussia in the Palaeozoic, subduction of oceanic and continental crust and their sedimentary cover introduced material of regionally contrasting chemical and isotopic compositions into the mantle. This slab material metasomatized 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 as 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 Al2O3 contents and high Mg-number) followed by strong metasomatic enrichment, giving rise to crust-like trace element pattern, 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 imprint 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. Fresh olivine from the Brloh (Moldanubian) lamproitic dyke shows very high Fo (up to 94 %) and very high Li contents (up to 25 ppm), demonstrating that the extremely depleted and later enriched lithospheric mantle may have contributed significantly to the Li budget of the lamproites. The regional distribution of lamproites with contrasting chemical and isotopic fingerprints mimics the distribution of the different Variscan subduction zones.

Keywords

Silica-rich lamproites, Sr-Nb-Pb-Li isotopes, mantle metasomatism, Rheic Ocean, Variscides

Authors

KRMÍČEK, L.; ROMER, R. L.; ULRYCH, J.; GLODNY, J.; PRELEVIĆ, D.

Released

1. 7. 2016

Publisher

Elsevier

Location

Amsterdam

ISBN

1342-937X

Periodical

GONDWANA RESEARCH

Year of study

2016

Number

35

State

Kingdom of the Netherlands

Pages from

198

Pages to

216

Pages count

19

URL

http://www.sciencedirect.com/science/article/pii/S1342937X15001240

BibTex

@article{BUT126641,
  author="Lukáš {Krmíček} and Rolf {Romer} and Jaromír {Ulrych} and Johannes {Glodny} and Dejan {Prelević}",
  title="Petrogenesis of orogenic lamproites of the Bohemian Massif: Sr–Nd–Pb–Li isotope constraints for Variscan enrichment of ultra-depleted mantle domains",
  journal="GONDWANA RESEARCH",
  year="2016",
  volume="2016",
  number="35",
  pages="198--216",
  doi="10.1016/j.gr.2015.04.012",
  issn="1342-937X",
  url="http://www.sciencedirect.com/science/article/pii/S1342937X15001240"
}