For constraining the age of mylonitic shearing in the Messaria shear zone and also the speed at which the Messaria extensional system slipped, we carried out Rb/Sr, 40Ar/39Ar, fission track and (U-Th)/He dating in the footwall of the Messaria extensional fault system. The data are not given here but can be found in Kumerics et al. (2005). Some of the sample localities will be described in the field trip section below.
Both analyzed samples are from the uppermost Ikaria nappe within the Messaria shear zone and they both are characterized by isotopic disequilibria. Detailed thin-section investigation of the quartzitic schist (sample IK99XD) suggests complete synkinematic recrystallisation; however, internal isotopic equilibrium on the mineral scale has not been achieved. On an isochron plot, the data only allow calculation of a loosely defined reference line corresponding to an age of 12.9±3.5 Ma (2σ errors). As no alteration features are observed, disequilibria are likely to correspond to preservation of isotopic relics. The age value is therefore interpreted as a maximum age for the last stages of mylonitisation.
The mylonitic metapegmatite sample IK02-4 shows severe Sr-isotopic disequilibria even for extremely deformed domains. For all analyzed white mica fractions, apparent ages have been calculated using the isotopic signature of apatite for reference. There is a clear correlation between sieve fraction (as a proxy for grain size) and apparent age for white mica separates. While the apparent age of 58±1 Ma for the 250-160 µm sieve fraction can be interpreted as a maximum age for deformation, the apparent age of 375±6 Ma for the 500-355 µm fraction points to only limited Sr isotope exchange among dynamically recrystallising phases and/or to presence of ground, but not recrystallised primary pegmatitic white mica. The apparent ages for slightly bent and kinked mica fish inner domains of 417±6 and 458±7 Ma are ‘mixed’ ages as well, without direct geological meaning. However, the oldest age of 458±7 Ma is a minimum age for protolith crystallization.
The latter age is poorly defined but strongly suggests to us that the magmatic event hat produced the pegmatite of the Ikaria nappe does actually belong to the Pan-African magmatic activity that is typical for parts of the Menderes nappes of adjacent western Turkey and underpins our tentative correlative of the Ikaria nappe to the Menderes nappes.
Mylonite: White mica from a mylonitic metapegmatite (IK02-4) and a metasediment (IK02-8) sample were dated with the spot-ablation technique. Both samples are intensely foliated and the foliation is made up by quartz, opaques and phengite, which is sheared and recrystallised in distinct foliation-parallel shear zones. The sections for 40Ar/39Ar dating are from the most thoroughly sheared and recrystallised parts of the samples.
In each section between 6 and 10 spots were analysed. The ages of IK02-4 range from 13.8±4.8 to 5.4±1.8 Ma and have a weighted mean age of 10.8±1.1 Ma (2σ errors). The ages from IK02-8 range from 11.1±0.3 to 9.5±0.5 Ma and show a weighted mean age of 10.5±2.4 Ma. We interpret the ages to date phengite recrystallisation during ductile deformation in the Messaria shear zone.
Altherr et al. (1982) reported K/Ar and Rb/Sr white mica ages of 11-10 Ma from metasediments in the footwall of the Messaria extensional fault system. Our detailed thin-section work on samples from localities where Altherr et al. (1982) collected their samples suggests that white mica completely recrystallised during mylonitisation. Therefore, we argue that mylonitisation and recrystallisation caused complete isotopic re-equilibration and that the K/Ar ages date mylonitisation-related mineral growth. The ages of Altherr et al. (1982) and our ages all young in a northward direction.
Muscovite and biotite crystals from granite samples IK1, IK2 and IK7 were analysed with the step-heating laser-probe technique. IK1 and IK2 are from the I-type Raches granite and IK7 from the S-type Xylosirtis granite. Biotite from sample IK2 yields a plateau age of 17.9±0.5 Ma (2σ errors) for 90% of released argon. Biotite from sample IK7 gives a plateau age of 10.7±0.3 Ma for ~81% of released argon, and muscovite from the same sample yields a slightly younger but within error similar plateau age of 10.2±0.5 Ma for ~100% of released argon. Biotite from sample IK1 gives an age of 9.3±0.9 Ma; however, because biotite was too small to provide a complete age spectrum this age is based on one single heating step only.
The 17.9 Ma biotite 40Ar/39Ar age from sample IK2 of the I-type Raches granite is much older than all other ages from this granite and its U-Pb zircon age (see below) and thus poorly understood.
The zircon fission track ages from the footwall of the Messaria extensional fault system range from 10.3±0.3 Ma in the south to 6.3±0.3 Ma in the north (2σ errors). The apatite fission track ages are between 8.4±0.8 Ma (south) and 5.2±0.9 (north) and the apatite (U-Th)/He ages range from 6.0±0.3 Ma (south) to 3.6±0.2 (north). All ages consistently young in a northward direction.
The samples from the hangingwall of the Messaria extensional fault system yielded no apatite and zircon. Fission track ages form the Ampelos nappe of Samos, which is correlative with the Messaria nappe in the hangingwall of the Messaria extensional fault system, range from 20-18 Ma (Kumerics et al. 2005; see Ring et al. for Samos in this volume).
We analysed zircons from sample IK2 from the I-Type Raches granite, from sample IK-05/7 from the S-type Karkinagrion granite and sample IK7 from the S-type Xylosirtis granite by excimer laser ablation (ELA-ICP-MS) at the Research School of Earth Sciences in Canberra, Australia. When combined these cores and rims yield the following pooled 206*Pb/238U ages: 13.8±0.3 Ma (N=31, MSWD=8.3) fro sample IK-2, 13.6±0.4 Ma (N=15, MSWD=5.1) for sample IK-05/7 and
14.2±0.3 Ma (N=9, MSWD=2.8) for sample IK7. All ages overlap with 2σ error. The ages became available just before this field trip guide was submitted and will thus no be discussed further.