Crustal Structures Of The Anatolia Plateau In Turkey And Its Comparison To The Himalaya-Tibetan Plateau

The Tethys Tectonic belt contains many segments,this giant tectonic belt records the evolution process of the Tethys Ocean from initial extension to terminal collisions.The study of East Tethys(Himalaya-Tibetan Plateau)has promoted large amounts of work on plate tectonics,surface geology,geophysics and geodynamic modelling to explain the uplift and post collision evolution of mountains and plateaus.The traditional“lateral extrusion” model suggests that with the collision between the Indian plate and Eurasia,the geological bodies inside and around the Himalaya-Tibetan Plateau extrude towards the oceanic free boundary.The model emphasizes rigid lateral extrusion and the oblique subduction induced thickening.However,the simple “lateral extrusion” model can’t explain the complex surface structure and the deep characteristics.Based on numerical modelling,it is proposed that the geodynamic evolution of the plateau is related to the thickening and “channel flow” of the ductile lower crust of the HimalayaTibetan Plateau.The geodynamical researches in the Himalaya-Tibetan Plateau are dominated with the purpose of supporting or falsifying the above two controversial endmember models.However,as the East Tethys continental collision process is coming to an end,it is difficult to distinguish and evaluate the effects of different geodynamic mechanisms on the uplift of the Himalaya-Tibetan Plateau.Thus,agreement has not been reached for the dynamic mechanism of the East Tethys.The geodynamics of the Himalaya-Tibetan Plateau needs to be compared with the tectonic evolution process in the early stage of collision,as preserved in Anatolia.The East Anatolian plateau in Turkey,located in the middle segment of the Tethys belt,is on the collision zone between the Arabian plate and the Eurasian plate,representing the early stage of the closure of the Neo-Tethys Ocean.Compared to the East Tethys,its geodynamic mechanism may represent the early stage of the northward subduction of the Indian plate to the Himalaya-Tibetan Plateau.Therefore,it is the best natural laboratory to compare the structure in East Tethys and test the proposed tectonic evolution process.This thesis demonstrates the potential problems existing in the interpretations of seismic receiver function with the synthetic tests,and propose the relevant improvements.High-quality crustal-mantle structure is acquired in Eastern Anatolian plateau,the geodynamic interpretation related to continental collision is proposed.The improved crustal structure for the whole Anatolia shows the relationship between crustal structure and lateral tectonic changes.Based on the study of deep structure,the seismic activity in the collision zone is then studied.The East and Middle Tethys are then compared from multiple disciplines to provide key evidence and new understanding for the tectonic evolution of the continental collision.The specific results are as follows:(1)In terms of method,through synthetic tests,the depth resolutions of receiver functions at different frequencies are discussed,and the potential misunderstandings in receiver function interpretation are put forward.Propose the method that use lowfrequency Bouguer gravity anomalies to calibrate the alternative or contrasting results from receiver functions.(2)The high-resolution seismic image in Eastern Anatolian Plateau is obtained.The new result reveals the main thrust fault which separates the plates of the hanging wall and footwall.The seismic research also reveals that the East Anatolia plateau have recently experienced the mantle underplating,and there are partial melting zones within middle crust.(3)The crustal structure of the whole Anatolian plate and surrounding regions is determined,and has been compared with the regional tectonic belts and the active structures.(4)The static Coulomb stress change pattern and the triggered seismicity of the low angle thrust fault in the collision zone is analyzed.The Coulomb stress modeling demonstrate that the main shock at the blind low angle thrust can induce the seismicity below the maximum slip zone,which is 10 ～ 20 km deeper than the fault zone.(5)Combined with the geophysical and geological studies of Eastern Anatolian Plateau,suggesting the seismic “double Moho” below the Lhasa block(previously interpreted as the lower crust of the Indian plate)may be the mafic continental lower crust layer formed by underplating.Mantle underplating plays an important role in the process of continental collision and uplift.