Emplacement dynamics of phonolite magma into maar-diatreme structures — Correlation of field, thermal modeling and AMS analogue modeling data Prokop Závada a, ⁎, Petr Dědeček a , Karel Mach b , Ondrej Lexa c , Marcel Potužák d a Geophysical Institute, Academy of Sciences of the Czech Republic, Boční II/1401, 141 31 Prague 4, Czech Republic b Severočeské doly a.s., Doly Bílina, ul. 5. května 213, 418 29, Bílina, Czech Republic c Institute of Petrology and Structural Geology, Charles University,Prague, Czech Republic d CORNING Inc., SP-FR-04 R4S12F, Corning, NY 148 31, USA abstract article info Article history: Received 28 January 2010 Accepted 18 July 2010 Available online 24 July 2010 Keywords: phonolite maar-diatreme magma emplacement dynamics thermal modeling AMS analogue modeling cavitation Emplacement mode and original shape and dimensions of a well exposed phonolite body in the České středohoří Mountains (Czech Republic) were reconstructed using combined techniques of structural analysis of magmatic fabrics and columnar jointing together with analogue and thermal mathematical modeling of cooling for different shapes of experimental bodies. Phreatomagmatic rocks in the vicinity of some phonolite stocks in the area of interest suggest that the phonolite bodies were likely emplaced into maar-diatremes. Our modeling revealed that intrusion of magma into phreatomagmatic maar-diatreme craters can result in cryptodomes, extrusive domes, lava lakes or branched intrusions. The fabric and columnar jointing pattern of the selected phonolite body reveals best fit with an asymmetric extrusive dome emplaced into the maar crater. The scaling analysis and thermal modeling also suggest that the phonolite extrusion could have formed within 6–66 days and cooled to the background temperature after 10,000 years. Combined analogue and thermal modeling also revealed that the phonolite extrusions into maar-diatreme craters are marked by upper tier (collonade) of vertical columns and lower tier of curved and outward flaring columns. Both tiers in the phonolite extrusions are divided by a subhorizontal suture. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Phonolite and trachyte bodies form expressive landmarks in several Tertiary intra-continental volcanic provinces in Europe. These provinces are associated with the rift systems of Rhein graben (Germany), Eger rift in Bohemian Massif (Czech Republic) and Limagne graben (France) that formed due to complex tectonic processes in the foreland of the Alpine orogeny (Fig. 1). Phonolite and trachyte magmas were emplaced during the last evolution stages of these rift systems (Camus, 1975; Kopecký, 1978). The emplacement mechanism and original shapes of phonolite and trachyte bodies are often poorly constrained, because of unknown paleosurface level and poor exposure of the host rocks in their surroundings, although they likely represent eroded remnants of cryptodomes, lava domes, laccoliths, lava flows or exposed volcanic conduits (Varet, 1971; Camus, 1975; Kopecký, 1978; Ulrych et al., 2000; Lorenz and Haneke, 2004; Závada et al., 2009b). A puzzling evidence in the phonolite bearing volcanic provinces is that both low- aspect ratio (coulées or thin laccoliths) and high-aspect ratio bodies (e.g. cryptodomes) can be found, which reflects either different local environment of the magma/lava emplacement (e.g. flat surface versus volcanic crater) or less likely the large variation in rheological properties of magma controlled by crystal content and melt chemistry (Dingwell et al., 1996; Saar et al., 2001; Giordano et al., 2004). Another unresolved feature of phonolite magma emplacement is that some individual phonolite bodies merge in plan-view with neighboring bodies, while others form solitary monuments. Earlier detailed studies of phonolites and trachytes attempted to define their emplacement mode using flow kinematics deduced from internal fabrics and fractures and considered the phonolite bodies as extrusion domes or “squeeze-up mounds” of highly viscous magma on the paleosurface (Cloos and Cloos, 1927; Varet, 1971; Jančušková et al., 1992; Arbaret et al., 1993; Závada et al., 2009b). In some cases, slices of basement rocks were reported to be uplifted by viscous drag of the magma along the steep walls of the intrusions (Varet, 1971; Kopecký, 1978). For a group of phonolite stocks close to Most town in the České středohoří Mountains in Bohemia (Fig. 1), Kopecký (1985) suggested that these represent teardrop shaped intrusions into maar-diatremes, while Fediuk (1985) proposed that these are only remnants of a differentially eroded coulée of phonolite lava. The first explanation is supported by outcrops of maar deposits in the vicinity of the phonolite stocks (Kopecký, 2000). Intrusion of magma into the maar-diatremes (phreatomagmatic volcanoes) is typical for the final stage of the phreatomagmatic volcano evolution, when the influx of water Journal of Volcanology and Geothermal Research 201 (2011) 210–226 ⁎ Corresponding author. Tel.: +420 267 103313; Fax: +420 272 761549. E-mail address: zavada@ig.cas.cz (P. Závada). 0377-0273/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2010.07.012 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores