Extensional Tectonics in Western Anatolia, Turkey: Eastward continuation of the Aegean Extension

Western Anatolia is located at the boundary between the Aegean and Anatolian microplates. It is considered a type-location for marking a significant transition between compressional and extensional tectonics across the Alpine-Himalayan chain. The onset of lateral extrusion in Western Anatolia and the Aegean during the Eocene is only one of its transitional episodes. The region has a geological history marked by diverse tectonic events starting from the Paleoproterozoic through the Cambrian, Devonian, and Late Cretaceous, as recorded by its suture zones, metamorphic history, and intrusions of igneous assemblages. Extension in Western Anatolia initiated in a complex lithospheric tectonic collage of multiple sutured crustal fragments from ancient orogens. This history can be traced to the Aegean microplate, and today both regions are transitioning or have transitioned to a stress regime dominated by strike-slip tectonics. The control for extension in Western Anatolia is widely accepted as the rollback of the African (Nubian) slab along the Hellenic arc, and several outstanding questions remain regarding subduction dynamics. These include the timing and geometry of the Hellenic arc and its connections to other subduction systems along strike. Slab tear is proposed for many regions across the Anatolian and Aegean microplates, either trench-parallel or perpendicular, and varies in scale from regional to local. The role of magma in driving and facilitating extension in Western Anatolia and where and why switches in stress regimes occurred along the Anatolia and Aegean microplates are still under consideration. The correlation between Aegean and Anatolian tectonic events requires a better understanding of the detailed metamorphic history recorded in Western Anatolia rocks, possible now with advances in garnet-based themobarometric approaches. Slab tear and ultimate delamination impact lithospheric dynamics, including generating economic and energy deposits, facilitating lithospheric thinning, and influencing the onset of transfer zones that accommodate deformation and provide conduits for magmatism.

Proterozoic zircon ages are found in the Pontides zone, but some of its central and 237 western granite assemblages also record Silurian-Devonian ages [Saricakaya, Table 4; is often mapped as closely and narrowly paralleling the Tavşanlı Zone, the southern extent of the 250 Afyon Zone is unclear, and a portion may also be exposed between the southern Menderes 251 Massif and Lycian Nappes (Okay, 1986 The Menderes Massif is considered the metamorphic basement on which the rocks of the 271 Afyon Zone were deposited before regional metamorphism (Okay, 1984). The Menderes Massif 272 exposes ~40,000 km2 of metamorphic and igneous rocks, and its stratigraphy was originally 273 described as a gneiss 'core' and Paleozoic schist envelope with overlying Mesozoic-Cenozoic 274 marble 'cover' (e.g., Schuiling, 1962;Durr, 1975;Şengör et al., 1984). The massif has also been 275 mapped as a large-scale recumbent fold (Okay, 2001;Gessner et al., 2002), a series of nappes 276 stacked during south-directed thrusting (Ring et al., 1999;Gessner et al., 2001), or north-277 directed thrusting (Hetzel et al., 1995a,b) (see Gessner et al., 2013). In the nappe model, the core 278 is represented by the Çine and Bozdağ nappes, whereas the cover would be the Bayındır and 279 Selimiye nappes , although all nappes may be part of the Menderes Massif 280 core series stacked during Eocene out-of-sequence thrusting (Régnier et al., 2007). Timeframes part of a collage of terranes associated with NE Africa and Arabia (Şengör et al., 1984; von 285 Raumer et al., 2015). Some Neoproterozoic zircons (ca. 570 Ma) have an older crust signature, 286 but others suggest a proximal juvenile source resembling the Arabian-Nubian shield (Zlatkin et 287 al., 2013). 288 Cambrian metagranites, orthogneisses, granulites, and ecologites, mica schists are related to the Cadomian Orogeny, and its core units were intruded by Pan African S-and I-type 294 granites followed by metamorphism (Neubauer, 2002). Note that other terranes within Western 295 Anatolia likewise have a Cadomian signature (Figure 4, e.g., Kozur & Göncüoğlu, 1998).         Kuscayir, and Kestanbol (Ezine), Figure 4, Table 5] and from a series of plutons grouped as the  and is currently active (Seyitoğlu, 1997;Ring & Collins, 2005

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The accretionary complex is unusual compared to others worldwide, not only because of these 604 back thrusts but also because it appears to have formed in a continent-continent collisional               are associated with retrogression instead of the desired prograde conditions. P-T paths that only 987 rely on core and rim measurements are also limited in their ability to test models developed 988 regarding lithospheric response to perturbations, including motion within fault zones.

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One promising avenue to address this issue is the application of isochemical phase 990 equilibria modeling. Figure 13 shows this approach applied to garnets from the Menderes  Figure 14A) and tectonic switching ( Figure 14B), which are briefly summarized 1024 here. Figure 14A and Figure 14B show an upper equilibrium thermal grid (depth vs. horizontal  Figure 14C and 1031 Figure 14D, the fault is active. A finite-difference solution to the diffusion-advection equation is 1032 used to examine the P-T variations in the hanging wall and footwall due to its motion. The rock 1033 sample experiences the point 1 to 2 in the P-T path insets. Fault motion stops and denudation 1034 occurs in Figure 14E and, whereas extension occurs in Figure 14F. This process is based on the 1035 mid-rim lower pressure portion of the garnet P-T path and is represented by points 2 to 3 on the 1036 P-T path insets. Although the end, the surface geometry in the denudation phase ( Figure 13E) 1037 and extensional phase ( Figure 14F) are similar, the shape of the isotherms is different and leads 1038 to the development of a decrease in temperature in the P-T loop observed in the tectonic 1039 switching model. Finally, the fault is reactivated, represented by Figure 14G to Figure 14H. The 1040 decrease in pressure with increasing temperature is related to an episode of denudation (model 1) 1041 rather than a tectonic switch from compression to extension (Etzel et al., 2019).

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The P-T paths reported in Figure 13 approximate how a garnet with specific 1043 compositional zoning would behave in a closed system of a known bulk composition as it 1044 evolves during increasing T. A critical assumption is that the minerals in a sample experienced 1045 equilibrium, which can never be proven for any rock system (e.g., Spear & Peacock, 1989;

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This paper is divided into two major sections. The first outlines, as much as is possible,        Geologische Rundschau = International Journal of Earth Science [1999], 105(1), 247-281.