Ar-39/Ar-40 ages from the Yozgat batholith: Preliminary data on the timing of Late Cretaceous extension in the central Anatolian crystalline complex, Turkey

Lo, Ching-Hua
Göncüoğlu, Mehmet Cemal
Demirel, Serhat
Isotopic dating of sheared and unsheared rocks can be important in understanding deformational processes in orogenic belts. This study examines Ar-40/Ar-39 dating of granitoids and mylonitic rocks to constrain intrusive and deformational events within the northern part of the central Anatolian crystalline complex (CACC). The Kerkenez granitoid within this complex, comprising primarily quartz monzonite and hornblende granite, contains discrete ductile shear zones. These zones are characterized by protomylonite and mylonite formations with metamorphism conditions that reach lower amphibolite facies, mylonitic foliations and lineations, and asymmetric kinematic indicators (e.g., asymmetric porphyroclasts, composite shear bands) with top-to-the-northwest shear senses. Considering the high closure temperatures (similar to 500 degrees C for hornblende and similar to 350 degrees C for K-feldspar), both hornblende quartz monzonite and hornblende granite in the Kerkenez granitoid may have cooled rapidly, suggesting that hornblende quartz monzonite may have been emplaced at around 81.2 +/- 0.5 Ma and that it is older than hornblende granite, which has a well-defined plateau age (72.6 +/- 0.2 Ma). On the basis of intrusive relations and our Ar-40/Ar-39 age data, we can constrain the upper age limit (similar to 81 Ma) on the regional metamorphism in the northern part of the CACC. The Ar-40/Ar-39 dating of hornblendes in two mylonite samples from a ductile shear zone yields plateau ages of 71.6 +/- 0.3 and 71.7 +/- 0.2 Ma, respectively. K-feldspars in the same samples yield plateau ages of 71.6 +/- 0.2 and 81.3 +/- 0.2 Ma. Therefore, we adopt 71.6 +/- 0.3 and 71.7 +/- 0.2 Ma as the cooling ages of hornblende and K-feldspar, respectively, in the ductile shear zone. On the other hand, an age of 81.3 +/- 0.2 Ma for deformed K-feldspar appears to reflect not the age of ductile deformation but rather the age of undeformed hornblende quartz monzonite. These age data suggest that the shear zones formed soon after the emplacement and cooling of hornblende granite. The cooling event of the shear zones is interpreted to be associated with the beginning of extension in the region. Furthermore, these data imply that metamorphism, emplacement, and cooling of the intrusives and ductile shearing of the intrusions were coeval in the region and occurred in the Late Cretaceous.


Bozkurt, Erdin; WINCHESTER, JA (Wiley, 1993-01-01)
The Menderes Massif, in western Anatolia, has been described as a lithological succession comprising a basal 'Precambrian gneissic core of sedimentary origin' overlain in sequence by 'Palaeozoic schist' and 'Mesozoic-Cenozoic marble' forming the envelope. The boundary between core and schist envelope was interpreted as a major unconformity, the 'Supra-Pan-African unconformity'. By contrast, our field observations and geochemical data show that around the southern side of Besparmak Mountain, north of Selimiy...
Mineralization events in a collision-related setting: The central anatolian crystalline complex, Turkey
Kuscu, I; Erler, A (Informa UK Limited, 1998-06-01)
Examination of mineral deposits in the Central Anatolian Crystalline Complex provides broad new insights regarding their genesis. Collision- and post-collision-related magmatic processes during closure of the northern branch of the Neotethyan Ocean, caused by northward subduction of the oceanic crust beneath the Sakarya Microcontinent in the Late Cretaceous-Eocene, led to the formation of several types of mineral deposits. These include: (1) skarn-type deposits (Pb-Zn, Fe, and Fe-W skarns); (2) vein-type de...
Crust–mantle interaction in western Turkey: Implications from Sr and Nd isotope geochemistry of Tertiary and Quaternary volcanics
Güleç, Nilgün Türkan (Cambridge University Press (CUP), 1991-01-01)
The isotopic composition of Sr and Nd together with the abundance data for major and trace elements are reported for Tertiary to Quaternary volcanics from a variety of localities in western Turkey. These data are used to evaluate the role of crust–mantle interaction in the petrogenesis of the western Turkish volcanics. The major and trace element chemistry reveals a general change in the nature of volcanism from dominantly calc-alkaline in Tertiary to alkaline in Quaternary times. The calc-alkaline rocks ar...
Palaeomagnetic evolution of the Cankiri Basin (central Anatolia, Turkey): implications for oroclinal bending due to indentation
Kaymakcı, Nuretdin; Langereis, Cor; White, Stan; van Dijk, Paul (Cambridge University Press (CUP), 2003-05-01)
Palaeomagnetic data in combination with palaeostress data and anisotropy of magnetic susceptibility orientations are utilized to develop a tectonic evolutionary model for the Early Tertiary part of the Omega(omega)-shaped Cankiri Basin (Turkey). The results reveal clockwise rotations in the northeast and anticlockwise rotations in the west and southeastern corner of the basin. The magnetic inclinations indicate a northward drift of the Cankiri Basin and support an indentation model for the Kirsehir Block. I...
Bozkurt, Erdin (Geological Society of London, 1994-03-01)
In the southern sector of the Menderes Massif, north of Selimiye (Milas) augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed Palaeozoic 'envelope'. The granitic rocks exhibit a moderately-dipping mylonitic foliation and NNE-SSW- trending mineral elongation lineation. The progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked, from bo...
Citation Formats
V. IŞIK, C.-H. Lo, M. C. Göncüoğlu, and S. Demirel, “Ar-39/Ar-40 ages from the Yozgat batholith: Preliminary data on the timing of Late Cretaceous extension in the central Anatolian crystalline complex, Turkey,” JOURNAL OF GEOLOGY, pp. 510–526, 2008, Accessed: 00, 2020. [Online]. Available: