Revision of Scheumann’s classification of melilitic lamprophyres and related melilitic rocks in light of new analytical data

Abstract

Dykes of the Late Cretaceous to Early Tertiary (79.5 ± 3.5 to 60.7 ± 2.4 Ma) melilitic rock series of the Osečná Complex and the Devil's Walls dyke swarm, including ultramafic lamprophyres -polzenites -of Scheumann (1913) occur dispersed in the entire Upper Ploučnice River basin in northern Bohemia. Polzenites and associated melilitic rocks are characterized by the mineral association of olivine + melilite ± nepheline, haüyne, monticellite, phlogopite, calcite, perovskite, spinels and apatite. New data on their mineral and chemical compositions from original Scheumann's localities (the Vesec, Modlibohov, Luhov types) argue against the abolition of the group of ultramafic lamprophyres and the terms 'polzenite' and 'alnöite' by the Le Maitre (2002) classification. Marginal facies and numerous flat apophyses of the lopolith-like body known as the Osečná Complex show an olivine micro-melilitolite composition (lamprophyric facies). The porphyritic texture, chemical composition and the presence of characteristic minerals such as monticellite and phlogopite point to their affinity with ultramafic lamprophyres -polzenites of the Vesec type. Melilite-bearing olivine nephelinites to olivine melilitites (olivine + clinopyroxene + nepheline + melilite ± haüyne and spinels with apatite) form a swarm of subparallel dykes known as the Devil's Walls. The Scheumann's non-melilite dyke rock "wesselite", spatially associated with polzenites and often erroneously attributed to the polzenite group, is an alkaline lamprophyre of monchiquite to camptonite composition (kaersutite + phlogopite + diopside + olivine phenocrysts in groundmass containing clinopyroxene, phlogopite, haüyne, analcime, titanian magnetite, apatite ± glass/plagioclase). First K-Ar data show Oligocene ages (30.9 ± 1.2 to 27.8 ± 1.1 Ma) and an affinity to the common tephrite-basanite rock series.

Chemistry and Sr-Nd isotope signature of amphiboles of the magnesio-hastingsite–pargasite–kaersutite series in Cenozoic volcanic rocks: Insight into lithospheric mantle beneath the Bohemian Massif

“…Phenocrysts/xenocrysts (1-2 cm) to megacrysts (up to 6 cm) in dykes of alkaline lamprophyres associated with the RIC of the CSVC (Skála et al, 2014): camptonite (Těchlovicesample 12), and maenite with the local name "gauteite" (Těchlovice and Divoká roklesamples 11, 13). Similar phenocrysts/xenocrysts come from camptonite with the local name "wesselite" from Veselí (sample 26) and camptonite dykes from Janův Důl (sample 27) in northern Bohemia (Ulrych et al, 2014).…”

Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry

“…The volcanism of this period predates the activation of the Ohře Rift and occurred in the rift external blocks of the graben, which formed later dur- (2008), Ulrych et al (2008Ulrych et al ( , 2013Ulrych et al ( , 2014. Note the very large variation and in some cases very high 87 Sr/ 86 Sr indicating melting of enriched mantle sources.…”

“…1) in the Upper Cretaceous and during the whole Cenozoic. Their production culminated in the pre-rift period (Late Cretaceous to Paleocene) in the Ploučnice River region in northern Bohemia (Ulrych & Pivec 1997;Pivec et al 1998;Ulrych et al 2008Ulrych et al , 2014 and in the late-rift period (Early to Late Pleistocene) in western Bohemia (Ulrych et al 2000a(Ulrych et al , 2011. A non-melilitic ultramafic rock association of Cretaceous age is known from the western part of the Outer Western Carpathians (Szopa et al 2014).…”

“…These rocks are concentrated in the Osečná Complex (Locality 9 in Fig. 1) situated at the intersection of the Lusatian Fault with the Ohře Rift (Ulrych & Pivec 1997;Ulrych et al 2008Ulrych et al , 2014. The Osečná Complex is formed by a central lopolith-like intrusion (Ulrych & Pivec 1997).…”

Lamprophyres from the Indian shield: A review of their occurrence, petrology, tectonomagmatic significance and relationship with the Kimberlites and related rocks

“…Although these rocks are volumetrically insignificant (<1%), they have profound implications for understanding enrichment and depletion processes in the sub-continental lithospheric mantle (SCLM, e.g., Guo et al, 2004;Krmíček et al, 2011Krmíček et al, , 2016Abdelfadil et al, 2013) and large scale-geodynamic processes (e.g., Tappe et al, 2006;Ulrych et al, 2014;Pandey et al, 2017a). Lamprophyres, together with other deep mantle-derived rocks such as kimberlites, lamproites and alkali basalt, are essentially restricted to the continental plates and their geochemistry provide invaluable clues with regard to probing the nature and evolution of the underlying mantle domains.…”