Petrology and geochemistry of the Tertiary alkaline intrusive rocks at Doupov, Doupovské hory Volcanic Complex (NW Bohemian Massif)

Abstract

Field observations, petrography, geochemical data and the results of K-Ar dating are presented for alkaline intrusions at the former township of Doupov (Duppau) in the central part of the Doupovské hory Volcanic Complex (DHVC). The Doupov Intrusive Complex (DIC) is a very limited in area (< 2 km 2 ) but is petrographically highly variable. Several phaneritic rock types have been identified, including clinopyroxenite (both the clinopyroxenite-dominated breccia and xenoliths in younger intrusive phases), essexite, sodalite-bearing monzodiorite, sodalite monzosyenite to nepheline-sodalite syenite, and highly mafic to felsic nephelinolites (melteigite-ijolite-urtite). These rocks are accompanied by vent breccias, and a thermal and metasomatic aureole with zones of pervasive phlogopitization. Phaneritic intrusions and their host rocks are cut by thin aphanitic dykes ranging from mafic alkaline lamprophyres to felsic trachytes and phonolites. All the intrusions are characterized by undersaturated alkaline compositions with high abundances of incompatible elements. Geochemical variations and also subtle differences in the isotopic compositions of Sr and Nd suggest that the less undersaturated essexitic rocks and sodalite syenitoids do not form a common evolutionary line with highly undersaturated nephelinolites. Nephelinolites are isotopically close to the "European Asthenospheric Reservoir" or the "Common Mantle Reservoir" compositions and interaction of their parental magmas with the continental crust was negligible. Magmatic evolution of nephelinolites with "dry" mineral assemblages was dominated by fractionation of clinopyroxene accompanied at the early stage by olivine, and later by titanite, magnetite and apatite. Essexite is isotopically more different though still within the field of mafic lavas from DHVC and other volcanic complexes in Central and Western Europe. Either its parental magma originated in heterogeneous mantle with more distinct lithospheric signature or this magma reacted with the continental crust during its ascent and fractionation. Sodalite monzosyenite displays significantly higher 87 Sr/ 86 Sr ratios and its parental magma probably interacted even more intensively with the crustal rocks. The K-Ar ages of phaneritic intrusive rocks from Doupov are c. 30-29 Ma. Intrusions are older than the tephrite-basanite and foidite lavas forming the upper parts of the DHVC. The rock association resembles that accompanying many carbonatite intrusions around the world. However, brecciation and high-temperature metasomatic overprint including the extensive phlogopitization may be related to ijolitic magma. Nevertheless, the presence of carbonatite at some deeper level cannot be excluded.

Magmatic evolution of compositionally heterogeneous monogenetic Cenozoic Strzelin Volcanic Field (Fore-Sudetic Block, SW Poland)

“…3 and illustrated in Fig. 8 (Rapprich and Holub 2008;Cajz et al 2009;Holub et al 2010;Ulrych et al 2016), and also within the Central European Volcanic Province (Jung and Masberg 1998; Lustrino and Wilson 2007). The Sr-Nd isotopic compositions of the nephelinites are less extreme, and resemble the samples from the Eger Rift (Cajz et al 2009;Holub et al 2010 (Fig.…”

Carbonate-rich dyke in Roztoky Intrusive Complex - an evidence for carbonatite magmatism in the Eger Rift?

“…The Sr-Nd isotope signature of R2 is also strikingly different from both primitive and evolved Cenozoic alkaline volcanic rocks in the Bohemian Massif (e.g., Haase and Reno 2008;Holub et al 2010;Ackerman et al 2015;Ulrych et al 2016;Fig. 7a).…”

“…For example, Kopecký (1987-88) reported on the presence of fenites and the involvement of carbonatite-related metasomatism was proposed for the alkaline intrusive centre in the Doupovské hory Volcanic Complex . Abundant carbonates of presumably magmatic origin were also described from Late Cretaceous to Early Paleogene alkaline ultramafic lamprophyres (Ulrych et al 1993, and magmatic (Ulrych et al 1983;Ulrych 1998;Ulrych and Balogh 2000;Skála et al 2014), and (b) the Doupov Intrusive Complex (DIC) in the centre of DHVC, with only the apical part exposed due to limited erosion (Haloda et al 2010;Holub et al 2010). The Loučná-Oberwiesenthal Intrusive Centre located on the Krušné hory/Erzgebirge shoulder of the Ohře/Eger Rift lacks the accompanying extrusive alkaline rocks (Ulrych et al 2005).…”

“…Extensive alkaline magmatism was associated with Cenozoic extension in Central and Western Europe (Wimmenauer 1974;Wilson and Downes 2006;Lustrino and Wilson 2007), including the Ohře/Eger Rift in the Bohemian Massif during the Oligocene and Miocene (e.g., Cajz et al 1999Cajz et al , 2009Holub et al 2010;Ulrych et al 2011).…”

Fingerprints of magma mingling processes within the Miocene Zebín tuff cone feeding system (Jičín Volcanic Field, Czech Republic)

“…Most of the magmatism was concentrated along the Eger Rift, which represents the easternmost branch of the European Cenozoic Rift System (e.g., Dèzes et al 2004;Rajchl et al 2008). Apart from the main volcanic complexes (see e.g., Ulrych et al 2002;Rapprich and Holub 2008;Cajz et al 2009;Holub et al 2010;Skála et al 2014;Ackerman et al 2015), several volcanic fields were formed also on the shoulders of the rift (Awdankiewicz 2005;Rapprich et al 2007;Büchner and Tietz 2012;Valenta et al 2014;Büchner et al 2015;Petronis et al 2015;Tietz and Büchner 2015;Awdankiewicz et al 2016;Ulrych et al 2016;Haase et al 2017). Our study focused on the Zebín Volcano, located in the Jičín Volcanic Field (Rapprich et al, 2007;Petronis et al 2015; Fig.…”