Obduction triggered by regional heating during plate reorganization

Abstract

The reason for obduction, or tectonic transport of oceanic lithosphere onto continents, is investigated by two-dimensional thermo-mechanical numerical modelling based on the geology of the Anatolia-Lesser Caucasus ophiolites. Heating of the oceanic domain and extension induced by far-field plate kinematics appear to be essential for the obduction of 80-Ma-old oceanic crust over distances exceeding 200 km. Heating of the oceanic lithosphere by mantle upwelling is evidenced by a thick alkaline volcanic series emplaced on top of the oceanic crust 10-20 Ma before obduction, at the onset of Africa-Eurasia convergence. Regional heating reduced the negative buoyancy and strength of the magmatically old lithosphere. Extension facilitated the propagation of obduction by reducing the mantle lithosphere thickness, which led to the exhumation of eclogite-free continental crust previously underthrusted beneath the ophiolites. This extensional event is ascribed to far-field plate kinematics resulting from renewed Neotethys oceanic subduction beneath Eurasia.

Neo-Tethys geodynamics and mantle convection: from extension to compression in Africa and a conceptual model for obduction

“…In this particular case, the age of the ophiolite should be older than the beginning of compression (i.e., provided by metamorphic sole ages). By contrast, the ophiolite in Armenia was much older at the time of obduction, and published models suggest the existence of an intra-oceanic subduction and a long-lived intra-oceanic back-arc domain where the ophiolite would have been rejenuvated before it was obducted (Rolland et al 2009;Hässig et al 2013Hässig et al , 2016.…”

“…Back-arc basins develop above the northern subduction zone, forming oceanic crust now flooring the Black Sea and the Caspian Sea and small back-arc domains in Central Iran (Hippolyte et al 2010;Nikishin et al 1998Nikishin et al , 2015aNikishin et al , 2015bAgard et al 2011). Since the Jurassic, an intra-oceanic subduction induces back-arc spreading, forming the ophiolite that will be obducted later on the northern margin of Apulia in Armenia (Hässig et al 2013(Hässig et al , 2016.…”

“…Label 22: Timing of subduction and obduction in Turkey (Çeliket al 2011;Pourteau et al 2013). Label 23: Timing of subduction and obduction in Armenia (Hässig et al 2013(Hässig et al , 2016Rolland et al 2009). Label 24: Timing of subduction and obduction in the Zagros Internal Zones (Agard et al 2006(Agard et al , 2005(Agard et al , 2011.…”

Early Cretaceous (Albian) intra‐oceanic subduction in northern branch of Neotethys in NW Iran: Zircon U–Pb geochronology and geochemistry of ophiolitic metagabbros from the Chaldoran area

“…The Khoy–Chaldoran ophiolite may be related to Neotethys 2 (“inner” Zagros ophiolites, Allahyari, Saccani, Pourmoafi, Beccaluva, & Masoudi, 2010; Hassanipak & Ghazi, 2000; Şengör, 1979). Some researches consider the Khoy‐Chaldoran ophiolite as a part of “outer” Zagros ophiolites, or Neotethys 1 (Khalatbari‐Jafari et al, 2004; Shafaii Moghadam & Stern, 2015) implying a significant obduction transport from the north (Hässig, Duretz, Rolland, & Sosson, 2016; Hässig, Rolland, Duretz, & Sosson, 2016).…”

Extrusion of subducted crust explains the emplacement of far-travelled ophiolites

“…Models of ophiolite emplacement hence have to account for (1) short-lived continental subduction below the oceanic upper plate followed by exhumation of the subducted upper crust, and (2) the observed dimensions of ophiolite sheets. Recent numerical modelling studies achieved these conditions by imposing convergence to reach the state of continental subduction, and subsequently imposing divergence to exhume the continental margin and thin the oceanic upper plate 6 , 12 . However, these models do not lead to nappe formation in the subducted continental crust, which is a key feature of natural systems and seems to play an important role in the exhumation of the HP-LT continental rocks 9 , 13 , 14 .…”