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Thermal histories of k-feldspar from granites located in the central and northern Menderes Massif, western Turkey: Implications for regional extension
  • Thomas Etzel,
  • Elizabeth Catlos,
  • Ibrahim Cemen
Thomas Etzel
University of Texas at Austin

Corresponding Author:[email protected]

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Elizabeth Catlos
University of Texas at Austin
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Ibrahim Cemen
The University of Alabama
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Evidence of syntectonic magmatism associated with onset extension and unroofing of the Menderes Massif metamorphic core complex, western Turkey, is well documented. The Salihli and Turgutlu plutons, located along the Alasehir detachment in the Central Menderes Massif (CMM) and the Koyunoba and Eğrigöz Plutons located in the Northern Menderes Massif (NMM) are common targets for understanding the dynamics and timing of this Cenozoic activity. To this end, here we report new potassium feldspar 40Ar/39Ar ages from samples collected from each pluton and compare these to available zircon U-Pb and monazite Th-Pb crystallization ages. Argon age spectra were collected by incrementally heating bulk concentrates with a CO2 laser and analyzing the gas released at each step. The peraluminous granite samples from the Koyunoba (AT17) and Eğrigöz (WA12) plutons both have effectively flat spectra with average plateau ages of 20.12±0.05 Ma and 19.86±0.05 Ma, respectively. The U-Pb age of zircon from WA12 is 20.5±1.1 Ma [Catlos et al., 2012; doi: 10.2475/05.2012.03 ]; although a zircon U-Pb age from AT17 has not been reported, zircon from other Koyunoba rocks have U-Pb ages between 21.1 Ma and 23.2 Ma [1]. K-feldspar from sample EB06 (Turgutlu Granite) steadily increases in age from 10.62±0.03 Ma to a plateau age of 14.06±0.03 Ma, with similar inverse isochron (13.66±0.29 Ma) and total gas ages (13.36±0.2 Ma). Sample EB05 (Salihli Granite) increases in age from 3.27±0.10 Ma (step 3, 0.5% 39Ar released) to a maximum of 6.05±0.09 Ma (step 33, 96.6% 39Ar released). A plateau age could not be estimated for this sample, but two inverse isochron ages from different degassing steps are calculated (3.02±0.09 Ma for the initial 19 steps and 3.29±0.22 Ma, for the final steps 19-31). Regarding their crystallization histories, the oldest reported monazite Th-Pb age for EB06 is 15.5±1.2 Ma [2] and reported monazite Th-Pb ages for Salhili granite ranges from 9.6±1.6 Ma to 21.7±4.5 Ma [Catlos et al., 2010; https://doi.org/10.1016/j.tecto.2009.06.001]. These 40Ar/39Ar ages suggest NMM plutons rapidly cooled whereas CMM Salihli and Turgutlu plutons not only remained at depth below the argon retention window for a prolonged period following emplacement, but each experienced unique thermal (exhumation) histories despite their geographic proximity.