EGU2020-9231, updated on 20 Jan 2021
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia

Salim Birkan Bayrak1, Işıl Nur Güraslan1, Alp Ünal1, Ömer Kamacı1, Şafak Altunkaynak1, and Erdinç Yiğitbaş2
Salim Birkan Bayrak et al.
  • 1Istanbul Technical University, Faculty of Mines, Geological Engineering Department, Istanbul, Turkey (
  • 2Çanakkale Onsekiz Mart University, Engineering Faculty, Geological Engineering Department, Çanakkale, Turkey

Marmara granitoid (47 Ma) is a representative example of the Eocene post-collisional magmatism which produced several granitic plutons in NW Anatolia, Turkey. It is a W-E trending sill-like magmatic body which was concordantly emplaced into the metamorphic basement rocks of Erdek Complex and Saraylar Marble. The granitoid is represented by deformed granodiorite which displays well-developed lineation and foliation in meso-scale defined by the elongation of mica and feldspar crystals and recrystallization of quartz however, in some places, magmatic textures are preserved. Deformed granodiorite is broadly cut by aplitic and pegmatitic dikes and contains mafic enclaves which display the same deformation indicators with the main granitoid.

Microstructural analysis shows that the solid-state deformation of the Marmara granitoid is classified as ductile deformation with high temperatures and ductile-to-brittle deformation with relatively lower temperatures. Evidence for the ductile deformation of the granitoid is represented by chessboard extinction of quartz, grain boundary migration (GBM) and subgrain rotation recrystallisation (SGR) which exhibits that the deformation temperature changed from 600 oC to 400oC. Bulging recrystallization (BLG), grain size reduction of amphibole, biotite and plagioclases and microcracks on plagioclases were considered as overlying ductile-to-brittle deformation signatures which develop between 300-<250 oC temperatures.

All of these field and micro-structural data collectively suggest that the shear sense indicators such as micafish structures and δ type mantled porphyroclasts displayed stair-steppings pointing out to a right lateral movement, indicating that the structural evolution and deformation history of Marmara granitoid was controlled by a dextral shear zone.

How to cite: Bayrak, S. B., Güraslan, I. N., Ünal, A., Kamacı, Ö., Altunkaynak, Ş., and Yiğitbaş, E.: Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9231,, 2020


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  • CC1: Comment on EGU2020-9231, Megan Mueller, 06 May 2020

    Birkan and co-authors, thanks for taking questions in the chat session. In the chat you indicated that dextral deformation was likely close to the emplacement age ~47 Ma. As a follow-up question, I'm curious about dextral shear in the Eocene. I would have thought it was related to ~Miocene North Anatolian Fault deformation. What's happening in the Eocene? Thanks, Megan

    • AC1: Reply to CC1, Salim Birkan Bayrak, 06 May 2020

      Dear Megan, thank you for your question :)
      Around Eocene time, there is a transition from compression to extension in NW Anatolia. This might cause the deformation, but it is debatable. 

      But the crust is thicker due to the previous collision, so for the generation of magma, there should be balancing forces to make the crust thinner. So that it can generate magma. These balancing forces might have created transtension, considering the traces of extension in the area. So this means that the generation of magma which created Marmara Granitoid may be related to this transtension, and also caused its deformation.

      We thought that the deformation in Marmara Granitoid is synkinematic, but we still don't have a clear idea on what caused the deformation. When we see a right lateral movement in Marmara Sea, it brings up a conversation about the North Anatolian Fault. Maybe we can see the traces of deformation which is caused by the NAF, or maybe the deformation which caused the Marmara Granitoid to be deformed is a part of the tectonic events which caused NAF to originate in the first place.

      This is only my undergraduate thesis, but hopefully I want to make more studies on NW Anatolia to understand all of these. So you can consider this a kind of a preliminary study, hopefully I will make more out of it.

      • CC2: Reply to AC1, Megan Mueller, 06 May 2020

        Birkan, yes, these are exciting preliminary results. A great accomplishment for an undergraduate project. Thank you for your reply. -Megan

    • AC2: Reply to CC1, Erdinç Yiğitbaş, 06 May 2020

      Dear Megan,

      I think that for pre-Miocene strike-slip tectonics and its significance could you please read the paper followings;

      Elmas A., Yiğitbaş E., "Ophiolite emplacement by strike-slip tectonics between the Pontide Zone and the Sakarya Zone in northwestern Anatolia, Turkey", INTERNATIONAL JOURNAL OF EARTH SCIENCES, vol.90, pp.257-269, 2001

      Yiğitbaş E., Elmas A., Yilmaz Y., "Pre-Cenozoic tectono-stratigraphic components of the Western Pontides and their geological evolution", GEOLOGICAL JOURNAL, vol.34, pp.55-74, 1999

      Best regards

      • CC3: Reply to AC2, Megan Mueller, 06 May 2020

        Dear Erdinç,

        I had not seen those papers. I look forward to reading them! Thank you.

        Warm regards,