Incipient Continent-Continent Collision and its impact on basement and sedimentary cover
Zusammenfassung der Projektergebnisse
The project CoCoCo takes advantage of two comprehensive geophysical surveys in the Eastern Mediterranean carried out in 2010. Each survey had to be performed in a different survey area from the initial planned survey area due to political reasons. The project CoCoCo was submitted in order to process and interpret the acquired data. The results of the project CoCoCo contributed significantly to the understanding of the complex interaction of the subducting African Plate and the overriding Eurasian Plate, south of Cyprus. Especially the transition from subduction to collision can be observed, in the form of the arrival of the Eratosthenes Seamount (a continental fragment) at the subduction trench. Within the project CoCoCo a huge amount of geophysical data was processed, interpreted and analyzed and published in the peer-reviewed journals. 1. Because of the dense grid of geophysical profiles we were able to image this important area with a high lateral and vertical resolution which led to a number of new and surprising results: The apparent lack of deformed sediments within the western Levant Basin. This led to the conclusion that the Eratosthenes Seamount, the Hecataeus Rise and the Levant Basin entered the subduction zone as one tectonic unit. There was no lateral displacement between the Eratoshenes Seamount and the Levant Basin, as a consequence there was no reactivation of the Baltim Hecataeus Line in the course of the collision of the Eratoshenes Seamount with the Cyprus Arc. 2. For us and for the community the discovery of thick salt layers in the subduction zone between Cyprus and Eratosthenes was the biggest surprise. Based on a dense grid of seismic reflection profiles, we report on compressional salt tectonics and its impact on the Late Miocene to Quaternary structural evolution of the Cyprus subduction zone. Results show that evaporites have experienced significant post-Messinian shortening along the plate boundary. Shortening has initiated allochthonous salt advance between Cyprus and Eratosthenes Seamount, representing an excellent example of salt which efficiently escapes subduction and accretion. Further east, between Eratosthenes Seamount and the Hecataeus Rise, evaporites were compressionally inflated without having advanced across post-Messinian strata. Such differences in the magnitude of salt tectonic shortening may reflect a predominately north–south oriented post-Messinian convergence direction, raising the possibility of a later coupling between the motion of Cyprus and Anatolia than previously thought. Along the area bordered by Cyprus and Eratosthenes Seamount a prominent step in the seafloor represents the northern boundary of a controversially debated semi-circular depression. Coinciding with the southern edge of the salt sheet, this bathymetric feature is suggested to have formed as a consequence of compressional salt inflation and seamount-directed salt advance. Topographic lows on top of highly deformed evaporites are locally filled by up to 700 m of late Messinian sediments. The uppermost 200 m of these sediments were drilled in the course of ODP Leg 160 and interpreted to represent Lago Mare-type deposits. Lago Mare deposits are spatially restricted to the western part of the subduction zone, pinching out towards the east whereas presumably continuing into the Herodotus Basin further west. We suggest a sea level control on late Messinian Lago Mare sedimentation, facilitating sediment delivery into basinal areas whereas inhibiting Lago Mare deposition into the desiccated Levant Basin. Locally, early salt deformation is believed to have provided additional accommodation space for Lago Mare sedimentation, resulting in the presently observed minibasin-like geometry. 3. The results from the amphibious seismic refraction / wide-angle reflection and gravity profile across the Eratosthenes Seamount (ESM), Cyprus and the Anatolian plateau in southern Turkey confirm that the ESM, with its crustal thickness of 32-35 km and crustal P-velocities predominantly lower than 6.5 km/s, is a fragment of continental crust. The observation is confirmed by marine magnetotelluric data, which shows continental crustal resistivities in the region. On Cyprus, the velocity distribution indicates an approximately 12 km thick ophiolite sequence resting mainly on lower crustal material. This, in turn, suggests that the ophiolite complex was obducted onto a rifted, thinned continental margin, although whether obduction was onto the Afro-Arabian margin to the south or the margin to the north cannot be differentiated. One surprise was to receive reflected phases from 45-50 km depth from the Moho of the subducting African plate beneath Cyprus. The identification of the Moho of the downgoing African plate both in this and a previous study, corroborates the evidence from teleseismic tomography that the downgoing slab is still present as a continuous unit under Cyprus and that the process of slab detachment has not yet fully ruptured the slab beneath Cyprus. Below the Anatolian plateau in southern Turkey rather large crustal thicknesses of 38-45 km were again encountered. 4. Results from magnetotelluric data profile from ESM to HR confirm the continental crustal character of ESM based on the fact that resistivities identified are typical for continental crust. Resistivties on HR show similar values, however, the crustal thickness seems to be thinner (25km - 30 km) compared to EMS (40km - 50km). A sub-vertical low resistivity feature situated between ESM and Hecataeus Rise in the upper mantle suggests the presence of a slab window and uprising of low resistivity mantle material. A lower crustal high resistivity anomaly in transition zone between ESM and HR may be associated with either a fragment of oceanic crust, mafic intrusion or represent an up-bending lithospheric feature associated with collision of tectonic plates.
Projektbezogene Publikationen (Auswahl)
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Crustal structure of the Eratosthenes Seamount, Cyprus and S. Turkey from an amphibian wide-angle seismic profile. AGU 2013 Fall Meeting, San Francisco, USA
Feld, C., Mechie, J., Hübscher, C. P., Gurbuz, C., Nicolaides, S., Weber, M., Hall, J., Louden, K. E.
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2014, Impact and implications of the Afro-Eurasian collision south of Cyprus from reflection seismic data, Tectonophysics, 626, 105-119
Jennifer Klimke and Axel Ehrhardt
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2014. Fault-controlled evaporite deformation in the Levant Basin, Eastern Mediterranean. Marine Geology, 354, 53-68
Reiche, S., Hübscher, C., Beitz, M.
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(2015, April). The impact of salt tectonics on supra-salt (Lago Mare?) deposits and on the structural evolution of the Cyprus-Eratosthenes collision zone. EGU General Assembly, Vienna, Austria
Reiche, S., Hübscher, C., Ehrhardt, A.
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2015. Crustal seismic velocity structure from Eratosthenes Seamount to Hecataeus Rise across the Cyprus Arc, eastern Mediterranean, Geophysical Journal International 200, 933-951
Welford, K., Hall, J., Hübscher, C., Reiche, S., Louden, K.
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2015. Crustal structure from the Hecataeus Rise to the Levantine Basin, eastern Mediterranean, from seismic refraction and gravity modelling. Geophysical Journal International 203(3), 2055-2069
Welford, K., Hall, J., Rahimi,A., Reiche, S., Hübscher, C., Louden, K.
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2015. The Hecataeus Rise, easternmost Mediterranean: A structural record of Miocene-Quaternary convergence and incipient continent-continent-collision at the African-Anatolian plate boundary. Marine and Petroleum Geology 67, 368-388
Reiche, S., Hübscher, C.
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2015. The impact of salt on the late Messinian to recent tectonostratigraphic evolution of the Cyprus subduction zone. Basin Research
Reiche, S., Hübscher, C., Ehrhardt, A.
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The Afro-Eurasian Collision south of Cyprus – New implication from reflection seismic data, DGG, Hannover
Jennifer Klimke and Axel Ehrhardt
