Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Vladislav Rapprich, Sarah Shields, Patricie Halodová, Jennifer Lindline, Benjamin van Wyk de Vries, Michael S. Petronis, Jan Valenta

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

Journal of Geosciences, volume 62 (2017), issue 4, 215 - 229

DOI: http://doi.org/10.3190/jgeosci.245

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 (Fo₉₀ to Fo₇₀ 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 simple 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.