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apatites and zircons were counted using immersion oil, whereas the induced tracks in
the muscovites were counted under dry objective. Data were collected with a
positioning tablet controlled by the computer program “FT Stage” (version 3.11)
developed by Dumitru (1993). The calculation of fission track ages was performed with
the computer program TRACKKEY 4.0 of Dunkl (2002). The apatite �-factor of
401.21±9.89 was determined from 10 apatite standards and the zircon �-factor of
122.91±2.09 is based on 7 zircon standards (Appendix C, Tab. C2 and C3). The � 2 test
was used to determine whether a fission track grain age distribution is homogeneous
or discordant (Galbraith 1981). Discordance is defined as grain ages with a variance
greater than expected for an analytical error alone. Mixed distributions can arise from
(a) sediments with unreset fission track ages, (b) differential resetting of grains with
different annealing properties due to variable compositions, or (c) variable alphadamage.
If the � 2 test of the probability of grains counted in a sample is >5%, a “pooled
age” is determined that depicts that the grains belong to a single age population. If � 2
is 125°C for apatite, tracks anneal immediately after their formation. No accumulation
of tracks occurs and the fission track age is zero. Between 60°C and 125°C a transitional
zone of partial track shortening exists. This zone is called partial annealing zone (PAZ).
Track-length reduction proceeds with increasing rates at higher temperature. At
temperatures