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

Continental subduction below oceanic plates and associated emplacement of ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit a far-travelled ophiolite sheet that is separated from its oceanic root by tectonic windows exposing continental crust, which experienced subduction-related high pressure-low temperature metamorphism during obduction. However, the link between continental subduction-exhumation dynamics and far-travelled ophiolite emplacement remains poorly understood. Here we combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the extrusion of subducted continental crust and the emplacement of far-travelled ophiolites. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. The broken-off piece of oceanic lithosphere is then transported on top of the continent along a flat thrust segment and becomes a far-travelled ophiolite sheet separated from its root by the extruded continental crust. Our results indicate that the extrusion of the subducted continental crust and the emplacement of far-travelled ophiolite sheets are inseparable processes.

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

<p>Continental subduction below oceanic plates and associated emplacement of ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit a far-travelled ophiolite sheet that is separated from its oceanic root by tectonic windows exposing continental crust, which experienced subduction-related high pressure-low temperature (HP-LT) metamorphism during obduction. However, the link between continental subduction-exhumation dynamics and far-travelled ophiolite emplacement remains poorly understood. We combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the extrusion of subducted continental crust and the emplacement of far-travelled ophiolite sheets. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. The broken-off piece of oceanic lithosphere is then transported on top of the continent along a flat thrust segment and becomes a far-travelled ophiolite sheet separated from its root by the extruded continental crust. Our results indicate that the extrusion of the subducted continental crust and the emplacement of far-travelled ophiolite sheets are inseparable processes.</p>

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

Continental subduction below oceanic plates and associated emplacement of far-travelled ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit continental rocks that experienced subduction-related high pressure-low temperature (HP-LT) metamorphism and subsequent exhumation coeval with the emplacement of ophiolites. However, the link between continental subduction dynamics and ophiolite emplacement is poorly understood. Here we combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the exhumation of subducted continental crust and ophiolite emplacement. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. This process is fundamental for the formation of a far-travelled ophiolite sheet that is separated from the oceanic domain by the exhumed, HP-LT continental upper crust. Our results indicate that the exhumation of the subducted continental crust and far-travelled ophiolite sheet emplacement are inseparable processes and thus shed light on one of the most mysterious aspect of plate tectonics.

Magmatic arcs, ophiolite belts and sedimentary basins in Anatolia interpreted from magnetic data

<p>Maps of depth to magnetic basement and crustal average susceptibility for the Anatolian plateau and adjacent regions are calculated by applying a spectral method to the magnetic data. The first map provides information on the shape of the sedimentary basins and the latter map is used for tracking magmatic arcs and ophiolite belts, which are covered by sediment and/or overprinted by different phases of magmatism and ophiolite emplacement. This is possible because magmatic and ophiolite rocks generally have the highest magnetic susceptibility values, and the huge contrast to sedimentary rocks makes magnetic data very useful.</p><p>The results shows a heterogeneous pattern associated with a mosaic of the many continental blocks, Tethyside sutures, magmatism and former subduction systems in Anatolia. Major basins such as northern part of the Arabian plateau, Black Sea basin, Mediterranean Sea basin and central Anatolian micro-basins are highlighted by very deep magnetic basement. Shallow magnetic basement is generally prominent in eastern Anatolia, and may represent that large amounts of magmatic rocks were emplacement during the convergence and compression of the Arabian plate, whereas a sporadic and asymmetric pattern of sedimentary basins in western Anatolia may have developed in the frame of the extensional regime. The average susceptibility map reveals extension of the Pontide magmatic arc in the north of Anatolia, following the coastline of the Black Sea. The average susceptibility indicates magmatism or ophiolite emplacement around the Kirşehır block. A 400 km long NW–SE elongated average susceptibility anomaly extends from south to NW of the Kirşehır beneath the Quaternary sediments, while the depth to magnetic basement indicate more than 6 km sediments. We speculate that this anomaly indicates a covered magnetic arc or a trapped part of oceanic crust. The westeward extension of the Urima-Dokhtar magmatic arc (UDMA) from the Iranian plateau fades away towards to Central Anatolian plateau. It suggest a geological boundary around the border between Iran and Turkey, which caused different magmatism between the two sides. A near zero magnetic anomaly in the Menderes massif region in the southwest of Turkey indirectly suggests a high geothermal gradient and hydrothermal activity that reduce the susceptibility of the rocks. This observation is in agreement with the crustal thinning and many geothermal fields of the Menderes massif.</p>

The syn- and post-obduction history of the offshore north Oman margin

<p>The offshore north Oman margin, located north of the Hajar Mountains in the Gulf of Oman,<br>remains a key area for understanding the evolution of the obduction Emails Ophiolite. With the<br>help of a grid of 2D-multichannel seismic lines linked to well data, we present a new view of<br>the obduction and post-obduction history of the Oman margin. Offshore deposits, overlying on<br>what we interpret as being the offshore extension of the ophiolites, can be divided into two<br>mega-sequences. The older one is comprised of late Cretaceous to Paleogene deposits mainly<br>located in the Sohar basin and offshore of the Abat trough. In the Sohar basin, the latest stages<br>of obduction are recorded by the deposition of the erosional products of the Autochthonous<br>Arabian sediments and the ophiolite, in a flexural basin induced by a volcanic high. Offshore<br>of the Abat trough, a Maastrichtian-Paleocene basin develops above a detachment fault<br>system linked to the extension phase associated to the exhumation/expulsion of the subducted<br>continental margin. Both sectors are divided by a structured high located offshore of the Semail<br>Gap transfer fault. We propose that this transfer fault, likely a major Pan-African structure,<br>impacted both the architecture of the passive margin following the rifting of the Neotethys and<br>later ophiolite emplacement, during (continental) subduction and obduction.</p>