Using 3D geodynamic slab models in tectonic reconstruction
In this thesis, two regions of convergent Cenozoic tectonics are investigated, and recent subduction is reconstructed using 3D models that map the surface of subducted slabs in the mantle. In Iran, the subduction of the Neotethys ocean prior to the collision of the Arabian continent with Eurasia is reconstructed, and the debates regarding the age of continental collision, slab tearing, and the generation of adakitic magmatism are examined. From the magnitude of reconstructed subducted lithosphere, a younger collision 28-27 Ma is favoured. Tearing of the slab along the margin occurs post-collision, initiating in the north-west at ~ 22 Ma and in central Iran at ~18 Ma. The second region of study is the Pamir and Hindu Kush. Seismic velocity anomalies and active deep seismicity here have led to numerous interpretations of the morphology of the subducted lithosphere in this region. Two possible interpretations are modelled and evaluated with reference to evidence from surface geology. Recent extensional tectonics, evidenced by the exhumation of detachment fault-bounded metamorphic domes, and geodetic evidence both favour a single Eurasian slab rolling back, and producing oroclinal bending in the Pamir. In the proposed model an extended basin once joined the Tarim and Tadjik, floored by oceanic lithosphere. Subduction was triggered as it was overridden by the advancing Indian continent, around the time of the Oligocene-Miocene boundary. Rapid rollback of the Pamir slab ahead of the advancing Indian continent explains current available evidence for extension and exhumation during an episode of large-scale collisional tectonics in the Miocene.
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