Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone (TOSCA)
Final Report Abstract
In recent years, there has been a growing realization 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. 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. Although this part of the CGFZ was recently declared as one of the first Marine Protected Areas in the high seas, the geological setting has not yet been studied in detail. The international and interdisciplinary RV Celtic Explorer expedition TOSCA (Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone) was realized in early summer 2018. The main objective of the cruise was to study the effects of long-lived asymmetric spreading and associated hydrothermal venting at the Charlie-Gibbs Fracture Zone in an interdisciplinary approach. Seismic imaging was integral part of the expedition; seismic imaging was realized in the frame of this proposal. Seismic data were collected with a high-resolution multichannel seismic system of Kiel University. Data were collected in two sedimentary basins in close vicinity to an oceanic core complex in the Charlie-Gibbs Fracture Zone. Bad weather conditions in combination with a faulty trigger box led to residual static shifts in the seismic data. A technique based on bathymetric data was successfully implemented to correct the residual static shifts. The seismic facies of the seismic units indicate that sediment accumulation in the basins is derived from bottom currents, pelagic sedimentation and mass wasting events. Mass transport deposits are less abundant than expected. An almost undisturbed thick sedimentary succession in the so-called NE basin was deposited with high accumulation rates of at least 7 cm/ka. Bottom currents are the most likely explanation for the high accumulation rates. The Iceland-Scotland Overflow Water (ISOW) flows through the CGFZ and may lead to the deposition of contourite drifts. The NE basin opened up because of extension resulting in normal faulting. Expansion of the basin may be ongoing and possibly compensated for in a clockwise rotation of the basin. The SW basin is located at the intersection of a transform fault with the Mid Atlantic Ridge. The morphology of this basin is more complex compared to the NE basin. Total sediment thickness is reduced and mass wasting is more abundant because the erosion of flanks of the oceanic core complex is higher towards the active transform faults.
Publications
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(2019) Initial results from the first detailed study of the Charlie-Gibbs Fracture zone. 62nd Irish Geological Research Meeting, UC Dublin, 01.03-03.03.2019
Judge, M., Georgiopoulou, A., Murton, B., Hollis, S., Yeo, I., Menuge, J., Collins, P., Robert, K., Scully, A., Dutrieux, A., Nomikou, P., McManus, O., Klein, E., Lohrberg, A., Krastel, S.
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(2019) Submarine landslide geohazards from Oceanic Core Complexes. Geophysical Research Abstracts, 21, EGU2019-1935
Georgiopoulou, A., Murton, B., Judge, M, Hollis, S., Krastel, S., Lohrberg, A., McManus, O., Nomikou, P., Robert, K., Scully, A., Yeo, I., Collins, P., Dutrieux, A., Klein, E.
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Giant landslide scarps on the Charlie-Gibbs Fracture Zone Oceanic Core Complexes; results from the TOSCA survey. 62nd Irish Geological Research Meeting, UC Dublin, 01.03- 03.03.2019
Georgiopoulou, A., Murton, B., Judge, M, Hollis, S., Yeo, I., Nomikou, P., Menuge, J., McManus, O., Collins, P., Robert, K., Scully, A., Klein, E., Lohrberg, A., Dutrieux, A., Krastel, S.
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(2020) Sediment basin evolution and architecture at the Charlie-Gibbs Fracture Zone, Mid-Atlantic Ridge. 80. Jahrestagung der DGG
Wilckens, H., Lohrberg, A., Gross, F., Georgiopoulou, A.,, Krastel, S.
