Shear wave velocity structure of the Anatolian Plate: anomalously slow crust in southwestern Turkey

Title of Publication: 
Shear wave velocity structure of the Anatolian Plate: anomalously slow crust in southwestern Turkey
Delph, Jonathan R., Biryol, C. Berk, Beck, Susan L., Zandt, George, and Ward, Kevin M.
Publication Info: 
Geophys. J. Int. (2015) 202, 261–276 doi: 10.1093/gji/ggv141 GJI Seismology

The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamated during the closure of the Paleotethys Ocean and Neotethys Ocean along a subduction margin. Using ambient noise tomography, we investigate the crustal and uppermost mantle shear wave velocity structure of the Anatolian Plate. A total of 215 broad-band seismic stations were used spanning 7 yr of recording to compute 13 778 cross-correlations and obtain Rayleigh wave dispersion measurements for periods between 8 and 40 s. We then perform a shear wave inversion to calculate the seismic velocity structure of the crust and uppermost mantle. Our results show that the overall crustal shear wave velocities of the Anatolian crust are low (∼3.4 kms−1), indicative of a felsic overall composition.We find that prominent lateral seismic velocity gradients correlate with Tethyan suture zones, supporting the idea that the neotectonic structures of Turkey are exploiting the lithospheric weaknesses associated with the amalgamation of Anatolia. Anomalously slow shear wave velocities (∼3.15 km s−1 at 25 km) are located in the western limb of the Isparta Angle in southwestern Turkey. In the upper crust, we find that these low shear wave velocities correlate well with the projected location of a carbonate platform unit (Bey Da˘glari) beneath the Lycian Nappe complex. In the lower crust and upper mantle of this region, we propose that the anomalously slow velocities are due to the introduction of aqueous fluids related to the underplating of accretionary material from the underthrusting of a buoyant, attenuated continental fragment similar to the Eratosthenes seamount.We suggest that this fragment controlled the location of the formation
of the Subduction-Transform Edge Propagator fault in the eastern Aegean Sea during rapid slab rollback of the Aegean Arc in early Miocene times. Lastly, we observe that the uppermost mantle beneath continental Anatolia is generally slow (∼4.2 km s−1), indicating higher than usual temperatures consistent with the influx of asthenosphere to shallow depths as a result of the segmentation and break-up of the subducting African lithosphere.

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Figure 1. (a) A map of the generalized geologic terranes of the eastern Mediterranean. AM, Anaximander Mountains; ATB, Anatolide-Tauride Block; BD, Bey Da˘glari; ES, Eratosthenes Seamount; KB, Kirs¸ehir Block; IAESZ, Izmir-Ankara-Erzincan Suture Zone; LN, Lycian appes; MM, Menderes Massif (after Okay & T¨uys¨uz 1999; van Hinsbergen 2010). The red triangles are late Cenozoic volcanic centres. (b) A map of the neotectonic setting of Turkey. Orange bars separate (from left to right) the Western Anatolian Extensional Province WAEP), Central Anatolian Province (CAP), and Eastern Anatolian Contractional Province (EACP) (S¸eng¨or et al. 1985). Geodetic displacement rates shown by thick black arrows (Reilinger et al. 2006). Diagonal lines show the approximate location of Isparta Angle. The haded region labelled FL is the Fethiye Lobe in the western Taurus Mountains. AB, Antalya Bay; BZS, Bitlis-Zagros Suture; CAFZ, Central Anatolian Fault Zone; CAVs, Central Anatolian Volcanics; CB, C¸ ankiri Basin; CTM, Central Taurus Mountains; DSFZ, Dead Sea Fault Zone; EAFZ, East Anatolian Fault Zone; EAP, East Anatolian Plateau; FBFZ, Fethiye-Burdur Fault Zone; FL, Fethiye Lobe; IA, Isparta Angle; KTJ, Karliova Triple Junction; NAP, North Anatolian Province; NEAFZ, Northeast Anatolian Fault Zone; NAFZ, North Anatolian Fault Zone; TGB, Tuz G¨ol¨u Basin; TGF, Tuz G¨ol¨u Fault. The red triangles are late Cenozoic volcanic centres.