Obduction of old oceanic lithosphere due to reheating and plate reorganization: Insights from numerical modelling and the NE Anatolia – Lesser Caucasus case example

Abstract

The ophiolites of NE Anatolia and of the Lesser Caucasus (NALC) evidence an obduction over ∼200km of oceanic lithosphere of Middle Jurassic age (c. 175–165Ma) along an entire tectonic boundary (>1000km) at around 90Ma. The obduction process is characterized by four first order geological constraints:(1)Ophiolites represent remnants of a single ophiolite nappe currently of only a few kilometres thick and 200km long. The oceanic crust was old (∼80Ma) at the time of its obduction.(2)The presence of OIB-type magmatism emplaced up to 10Ma prior to obduction preserved on top of the ophiolites is indicative of mantle upwelling processes (hotspot).(3)The leading edge of the Taurides-Anatolides, represented by the South Armenian Block, did not experience pressures exceeding 0.8GPa nor temperatures greater than ∼300°C during underthrusting below the obducting oceanic lithosphere.(4)An oceanic domain of a maximum 1000km (from north to south) remained between Taurides-Anatolides and Pontides-Southern Eurasian Margin after the obduction.We employ two-dimensional thermo-mechanical numerical modelling in order to investigate obduction dynamics of a re-heated oceanic lithosphere. Our results suggest that thermal rejuvenation (i.e. reheating) of the oceanic domain, tectonic compression, and the structure of the passive margin are essential ingredients for enabling obduction. Afterwards, extension induced by far-field plate kinematics (subduction below Southern Eurasian Margin), facilitates the thinning of the ophiolite, the transport of the ophiolite on the continental domain, and the exhumation of continental basement through the ophiolite. The combined action of thermal rejuvenation and compression are ascribed to a major change in tectonic motions occurring at 110–90Ma, which led to simultaneous obductions in the Oman (Arabia) and NALC regions.