Emplacement depths and radiometric ages of Paleozoic plutons of ...

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Several plutons, predominantly of granitic composition,
intruded into or adjacent to the WBSZ and
CBSZ, parts of them synkinematically (Scheuvens,
1999; Zulauf et al., 2002). Lower Carboniferous
emplacement ages, ranging from ca. 330 to 350 Ma,
have been determined for these intrusions by U–Pb
and Pb–Pb zircon dating (e.g., Bor pluton, Mutěnín
pluton, Babylon granite, Drahotín gabbro, Klatovy
pluton, Ny´rsko pluton; Dörr et al., 1997; Central
Bohemian pluton; Holub et al., 1997). Only the
Teufelsberg (Čertu˚v kámen) diorite yields an Upper
Devonian age (see below).
In contrast to the TBU, the Moldanubian unit is
characterized by widespread Carboniferous granitoids
and anatexis, the age of which has recently been
determined at 322–326 Ma (U–Pb on zircon and
titanite, 40 Ar– 39 Ar on hornblende, Kalt et al., 2000).
Lower grade mica schists and gneisses are restricted to
the Královsky Hvozd crystalline complex, a Moldanubian
subunit situated SE of the NKM (Fig. 1). In
this area, metapelitic rocks partly contain kyanite
relics of an early medium pressure metamorphism
(Vejnar, 1991; Babu˚rek, 1995), suggesting a multistage
metamorphic evolution within parts of the
Moldanubian unit. The age of this medium pressure
metamorphism (i.e., Cadomian or Variscan) has yet
not been determined. However, microspores preserved
within low grade metamorphic mica schists near
Rittsteig suggest a Paleozoic protolith for at least
parts of the Královsky Hvozd metasediments (Reitz,
1992). Apart from these mica schists, the Moldanubian
unit adjacent to the study area consists of a
prograde succession of andalusite-bearing mica
schists, cordierite sillimanite gneisses, and cordierite
K-feldspar anatexites (Blümel, 1990).
3. Methods
The composition, emplacement depth, cooling history,
and tectonometamorphic overprints of granodiorite,
diorite, and gabbro of the Vsˇepadly, Smrzˇovice,
Orlovice, Vsˇeruby, Neukirchen, Teufelsberg, and
Hoher–Bogen–Rittsteig areas have been investigated
(for localities, see encircled numbers 1–8 in Fig. 1).
In the case of the Teufelsberg pluton, we also determined
the protolith age. Geobarometric and geothermometric
data were derived from the chemical
C. Bues et al. / Tectonophysics 352 (2002) 225–243
compositions of olivine, pyroxene, amphibole, biotite,
and feldspar, which were analysed at the Technische
Universität Darmstadt and the Universität Würzburg
using a Cameca SX-50 electron microprobe. The
operating conditions were similar to those reported
in Bues and Zulauf (2000). Summaries of representative
mineral analyses are listed in Table 1. The mineral
abbreviations used throughout the text are according
to Kretz (1983).
We applied the geothermometer of Blundy and
Holland (1990) and Holland and Blundy (1994) to
calculate equilibration temperatures of hornblende and
plagioclase for the Vsˇepadly granodiorite and Smrzˇovice
quartz diorite. These rocks also contain the
appropriate buffer assemblage required for the Al-in-
Hbl barometry according to Schmidt (1991) and
Anderson and Smith (1995). Equilibration temperatures
of orthopyroxene and clinopyroxene were calculated
for the Smrzˇovice, Vsˇeruby, and Teufelsberg
pyroxene diorite using the TWQ program of Berman
(1991) together with the revised thermodynamic database
of Berman et al. (1995) and Berman and Aranovich
(1996). This method was also applied to the
Opx–Cpx–Spl corona of the olivine metagabbro of
the eastern Hoher–Bogen area. For the Vsˇeruby
olivine gabbro and gabbronorite, we additionally used
the Opx–Cpx geothermometer of Wells (1977).
To carry out K–Ar analyses of hornblende and
biotite, mineral separation was performed in the
laboratory of the geological institute of the AVČR
(Prague) using standard techniques, such as crushing,
sieving, flotation, Frantz magnetic separation, and
hand picking. K–Ar analyses were carried out in the
laboratory of the Bundesanstalt für Geowissenschaften
und Rohstoffe (BGR, Hannover) using flame
photometry and noble-gas mass spectrometry for
K–Ar determination. Details of sample processing
are given by Kreuzer et al. (1989). All errors quoted
were calculated on the 95% (2r) confidence level.
Zircons of the Teufelsberg pluton (locality
‘Hoher–Stein’) have been separated and abraded
(for the separation and analytical techniques, see also
Dörr et al., this volume). Dissolution and separation of
U and Pb were carried out after Krogh (1973). Each
single zircon was placed in a Teflon vessel within an
autoclave and digested over 6 days at 180 jC with 24
N HF. After cooling, a mixed 235 U– 208 Pb spike was
added to one-third of the solution of the zircon to