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

Abstract

A well-preserved set of partly eroded mid-Miocene scoria cones and tuff cones are exposed in the Jičín Volcanic Field, Czech Republic. Zebín Hill, a formerly quarried tuff cone with an exposed conduit and associated dikes, offers an opportunity to study magmatic processes within the high-level feeding system of a small monogenetic volcano. Two types of dikes and associated "blob-like" intrusions were observed. Pure basanite dikes predominate in the center of the cone, whereas its peripheries were intruded by mingled dikes. The mingled dikes consist of mm-scale basanitic domains enclosed in a network of trachyandesitic dikelets. Locally, hybrid domains with intermediate characteristics were observed. The basanite dikes and basanite enclaves within mingled dikes contain normally-zoned minerals (Fo 90 to Fo 70 olivine, Mg-rich to Mg-poor diopside, labradorite to andesine composition of plagioclase) indicative of basanite magma evolution during ascent. In contrast, the trachyandesite and hybrid enclaves in mingled dikes show reverse zoning of minerals (Mg-poor to Mg-rich diopside, sanidine to oligoclase feldspar composition) indicative of magma hybridization. This study suggests that the Zebín Volcano did not develop from a simple monogenetic system and through a single central axis feeder; rather, Zebín Hill evolved from a complex magma feeding/storage system and through a complex feeder network. We conclude that the simple external structure of a monogenetic volcano may sometimes hide rather complex magmatic plumbing systems encompassing compositionally contrasting rocks/magmas.

Petrogenesis of Miocene subvolcanic rocks in the Western Outer Carpathians (southeastern Moravia, Czech Republic)

“…The negative correlation between Mg and Ti (Fig. 3b) in diopsides from gabbro enclaves and trachydacite can be explained by decompression during fractional crystallization (e.g., Tracy and Robinson 1977;Rapprich et al 2017). The amphibole compositional trends for leucocratic and melanocratic gabbro enclaves are similar to those for the amphibole from the host-rock (trachydacite, Fig 3d).…”

“…Rock-forming mineral compositions for the subvolcanic rocks and gabbro enclave: a -Ternary En (MgSiO 3 )-Wo (CaSiO 3 )-Fs (FeSiO 3 ) classification diagram(Morimoto et al 1988); b -Mg vs. Ti diagram illustrating the clinopyroxene compositions; arrow shows approximately the direction of compositional shift due to fractional crystallization (e.g.,Tracy and Robinson 1977;Rapprich et al 2017); c -Ternary Ab-An-Or diagram (mol. %) of feldspars; d-e -Mg/(Mg+Fe 2+ ) vs. Si (apfu) classification diagrams of calcic amphiboles with Ca B ≥ 1.5(Leake et al 1997) containing (Na + K) A ≥ 0.5 and (Na + K) A < 0.5, respectively; f -Ti vs. IV Al diagram for calcic amphiboles; arrow shows approximately the direction of compositional shift due to fractional crystallization (e.g.,Tiepolo et al 2011).…”

The Way to the Rocks—Changes of Networks of Hiking Trails in Chosen Sandstone Landscapes in Poland and the Czech Republic in the Period of Political Transformation

“…Stratigraphy includes rock series from the Cenomanian to the Coniacian (Migoń and Pijet-Migoń 2006;Uličný 2001;Uličný et al 2009). The relief was also influenced by Neogene volcanism, which is reflected today in locally present necks and lava covers (Petronis et al 2015(Petronis et al , 2018Rapprich et al 2007Rapprich et al , 2017b. Currently, the entire Bohemian Paradise has been recognised not only as a protected landscape area (what happened already in 1955), but also-in 2005 as the first such area in the Czech Republic-as a geopark, being now a member of national, European and global geopark networks (Kubalíková 2018;Migoń and Pijet-Migoń 2006).…”

The Stolpen Volcano in the Lausitz Volcanic Field (East Germany) - volcanological, petrographic and geochemical investigations at the type locality of basalt

“…The investigated Stolpen lava samples implicate an inhomogeneous lava body given the combined observations of (1) incorporated melt enclaves of chemically different but genetically associated lava, and (2) inclusions of country rocks or their fragments. Magmatic enclaves are the result of incomplete magma mixing (Didier and Barbarin 1991) and represent a common phenomenon in large lava bodies in the Lausitz Volcanic Field (Wenger et al 2017, see also Rapprich et al 2017). These cognate enclaves (sensu Didier and Maury 1991) imply diverse magmatic sources for the Stolpen magma likely induced by fractionation below the surface, or independent magma batches.…”