Discovery of the
first Quaternary maar in the Bohemian Massif, Central Europe, based
on combined geophysical and geological surveys
J. Mrlina
a
,
⁎
, H. Kämpf
b
, C. Kroner
b
, J. Mingram
b
, M. Stebich
c
, A. Brauer
b
, W.H. Geissler
d
,
J. Kallmeyer
b
,
f
, H. Matthes
e
, M. Seidl
a
a
Institute of Geophysics ASCR, Bo
ční II/1401, 14131 Prague 4, Czech Republic
b
Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, D-14473 Potsdam, Germany
c
Senckenberg, Forschungsinstitute und Naturmuseum, Forschungsstation für Quartärpaläontologie, Am Jakobskirchhof 4, D-99423 Weimar, Germany
d
Alfred Wegener Institute for Polar and Marine Research, Am Alten Hafen 26, D-27568 Bremerhaven, Germany
e
Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg, D-14473 Potsdam, Germany
f
University of Potsdam, Department of Geosciences, Karl-Liebknecht-Str. 27, Haus 27, 14476 Potsdam, Germany
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 31 August 2008
Accepted 30 January 2009
Available online 8 February 2009
Keywords:
Eger Rift
Quaternary maar volcanism
geophysical survey
Saalian lake sediments
volcanic hazard potential
Based on results of previous investigations of tephra-tuff volcaniclastic deposits and a geophysical survey in
the surroundings of the
Železná hůrka Quaternary volcano, West Bohemia, we performed detailed geo-
physical surveys using gravimetry, magnetometry and electrical conductivity techniques. Striking anomalies
were revealed in a morphological depression near Mýtina, West Bohemia, as a strong evidence of the assumed
maar-diatreme structure. The sharp isometric gravity low of
−2.30 mGal, as well as the corresponding positive
magnetic anomaly of 200 nT with a negative rim on its northern side indicate a steeply dipping geological body
of low density and containing magnetic rocks/minerals. Magnetic survey also showed pronounced local
anomalies outside the depression that can re
flect relicts of the tephra rim of the maar.
This geophysical evidence was then proven by an exploratory drilling near the centre of the gravity anomaly.
Macroscopic on-site evaluation of the core, and more detailed sedimentological, petrochemical, palynological
and microbiological laboratory analyses further con
firmed the existence of a maar structure filled by 84 m of
lake sediments re
flecting a succession of several warm and cold climatic periods. Results of palynological
analyses con
firm the presence of a continuous palaeoclimate archive, with at least three successive warmer
periods of most probably interstadial character from the upper Quaternary Saalian complex. Therefore, the
recovered sediment sequence holds strong potential for in-depth paleoclimate reconstruction and deep bio-
sphere studies.
At the bottom of the Mýtina-1 (MY-1) borehole (84
–85.5 m), country rock debris was found, containing also
volcanic bombs and lapilli.
The discovered volcanic structure is considered to be the
first known Quaternary maar-diatreme volcano on the
territory of the Bohemian Massif. Because of hidden active magmatic processes in combination with earth-
quake swarm seismicity ca. 20
–30 km north of the Mýtina maar, reconstruction of the palaeovolcanological
evolution is important for evaluation of hazard potential of the NE and E part of the Cheb Basin.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Maar-diatreme volcanoes are the most common volcano type
following scoria cones. The Westeifel, Germany, is the classical area for
maar-diatreme volcanoes worldwide with more than 68 of such
structures of Quaternary age (
Büchel and Pirrung, 1993
). Maar-
diatreme volcanoes develop when magma rises in dykes and
intersects with water causing thermohydraulic explosions (
Lorenz
et al., 2003
). Up to now several Tertiary maar-diatreme volcanoes are
known from the northern part of the Bohemian Massif (
Brus & Hurnik,
1984; Lindner et al., 2006; Kopecky, 1968; Krutsky, 1994; Malasek
et al., 1980; Rutsek, 1973; Suhr & Goth, 1996; 1999; Wiedemann, 1961
),
which are related to volcanic activity of the Eger Rift. The Eger Rift
(
Kopecky, 1978; Mrlina, 1980
) is part of European Cenozoic Rift
System (ECRIS;
Ziegler, 1992
). Within ECRIS Quaternary maar
volcanoes are well known from the French Massif Central and the
western Eifel (
Fig. 1
, inset map).
Journal of Volcanology and Geothermal Research 182 (2009) 97
–112
⁎ Corresponding author.
E-mail addresses:
jan@ig.cas.cz
(J. Mrlina),
kaempf@gfz-potsdam.de
(H. Kämpf),
kroner@gfz-potsdam.de
(C. Kroner),
ojemi@gfz-potsdam.de
(J. Mingram),
mstebich@senckenberg.de
(M. Stebich),
brau@gfz-potsdam.de
(A. Brauer),
wolfram.geissler@awi.de
(W.H. Geissler),
jens.kallmeyer@geo.uni.potsdam.de
(J. Kallmeyer),
heidrun.matthes@awi.de
(H. Matthes),
michal.seidl@ig.cas.cz
(M. Seidl).
0377-0273/$
– see front matter © 2009 Elsevier B.V. All rights reserved.
doi:
10.1016/j.jvolgeores.2009.01.027
Contents lists available at
ScienceDirect
Journal of Volcanology and Geothermal Research
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j v o l g e o r e s