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

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Table 2
Analytical data of K–Ar age determinations on biotite and hornblende. Argon concentrations in nanoliter per gram at standard conditions (nl/g
STP); potassium concentrations in weight percentage (wt.%)
Sample Locality Mineral Fraction (Am) K (wt.%) Radiogenic Ar Date (Ma)
(nl/g STP) (%)
PAM27F Hoher–Stein biotite 125–63 6.75 98.89 99.1 342 F 4
113 quarry Smrzˇovice biotite 250–125 6.94 153.80 98.8 495 F 6
SK4 quarry Smrzˇovice hornblende 125–63
(magnetic fraction)
0.26 6.49 91.7 547 F 7
SK4 quarry Smrzˇovice hornblende 125–63
(unmagnetic fraction)
0.27 6.81 91.9 549 F 7
Mean standard deviation (2r) of radiogenic argon is about 0.3% and of potassium about 1% for high-K and low-K materials, respectively. The
error in the K –Ar apparent age is given at the 95% confidence level. Note that our K–Ar date for the standard glauconite GL-O is about 1%
younger than the mean value of the compilation of Odin (1982).
dip–slip or slightly oblique-slip lineation portrayed
by stretched plagioclase or by the long axes of
amphibole. Non-coaxial top–down-to-the-NE normal
movements are indicated by asymmetric amphibole
porphyroclasts (j- and y-clasts) and by shear band
fabrics (see Table 1A in Bues et al., 1998).
5. Depth of pluton emplacement
Using the geothermometers and geobarometers
mentioned above and shown in Fig. 6, we calculated
the following temperatures and pressures. For granodiorite
and quartz diorite of the Vsˇepadly and
Smrzˇovice intrusion, the equilibration temperatures
of hornblende and plagioclase are in the range of
Fig. 7. Cathodoluminescence image of a zircon separated from the
Teufelsberg diorite (for further explanation, see text).
C. Bues et al. / Tectonophysics 352 (2002) 225–243
620–680 jC (Fig. 6A and B). Low crystallization
pressures of hornblende (1.5–3 kbar; Fig. 6A and B)
indicate emplacement at shallow crustal levels. Higher
equilibration temperatures of 830–920 jC were calculated
for pyroxene diorite of the Smrzˇovice, Vsˇeruby,
and Teufelsberg intrusion (Fig. 6C and E) that do
not show the appropriate mineral assemblage for
using the Al-in-Hbl barometry. For the Smrzˇovice
pyroxene diorite, the pressure should be similar to
that of the quartz diorite from the same locality. For
the Vsˇeruby and Teufelsberg pyroxene diorite, we
have inferred the pressure from the corona microfabrics
that occur in the associated olivine gabbros
(see below). Ortho- and clinopyroxene equilibration
temperatures up to 980–1080 jC have been derived
from olivine gabbro and gabbronorite of the Vsˇeruby
intrusion (Fig. 6D). Equilibration temperatures of
reaction rims between olivine and plagioclase are
Fig. 8. Concordia diagram for zircons from the Teufelsberg diorite
(locality Hoher–Stein).