Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone (TOSCA)

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In recent years, there has been a growing realisation that seafloor spreading at many slow and ultra-slow spreading mid-ocean ridges is accommodated not by volcanism, but by tectonic stretching resulting in the dissection of the oceanic crust and exhumation of the underlying mantle. The resulting structures are known as oceanic core complexes; they expose lower crustal and upper mantle rocks in the footwalls of long-lived, low-angle detachment faults.Conditions at the central rift of the Charlie-Gibbs Fracture Zone have the optimum attributes for the development of oceanic core complexes. The Charlie-Gibbs Fracture Zone is a major fracture zone that offsets the Mid-Atlantic Ridge approximately 350 km left-laterally, between Iceland and the Azores (52° to 53° N). It comprises two seismically active E-W transform-fault valleys separated by a short ridge. The scheduled RV Celtic Explorer Expedition TOSCA (Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone) will take place from May 13th to June 7th 2018. The main objective of this cruise is to study the effects of a long-lived asymmetric spreading and associated hydrothermal venting at the Charlie-Gibbs Fracture Zone in an interdisciplinary approach. An integral part of the work is the collection of high-resolution reflection seismic data in order to image the sedimentary sequence infilling the Charlie-Gibbs Fracture Zone troughs. These data should be collected by means of the high-resolution seismic system of Kiel University. Main objectives addressed by seismic surveying include i) the investigation of the mechanism by which mid-ocean ridges get destroyed and buried away from the spreading centres, ii) to map deep-seafloor mass wasting deposits in the troughs as a record of past seismic activity, and iii) to image the basement topography. The Charlie-Gibbs Fracture Zone is so poorly known that we can look at the recovery of any data and material as a true exploration that will increase our knowledge and understanding of this critical region.