Structure of Mesozoic oceanic crust in the vicinity of the Cape Verde Islands from seismic reflection profiles
- PDF / 1,560,685 Bytes
- 15 Pages / 595 x 842 pts (A4) Page_size
- 62 Downloads / 172 Views
Ó Springer 2005
Structure of Mesozoic oceanic crust in the vicinity of the Cape Verde Islands from seismic reflection profiles M.Y. Ali1,3, A.B. Watts1,* & I. Hi1l2 1
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK; 2Department of Geology, University of Leicester, University Road, Leicester LE 7RH, UK;3Present address: The Petroleum Institute, P.O. Box. 2533, Abu Dhabi, UAE; *Author for correspondence (Phone: +44-1865-272032; Fax: +44-1865-272072; E-mail: [email protected])
Received 7 November 2003; accepted 15 September 2004
Key words: Cape Verde islands, seismic reflectors, oceanic crust, fracture zones, flexure, Moho
Abstract Multichannel seismic reflection profile data have been used to determine the internal structure of Mesozoic oceanic crust in the vicinity of the Cape Verde islands. The data show the oceanic crust to be characterized by both dipping and sub-horizontal reflectors. Several lines of evidence argue against the reflectors being scattering artifacts arising, for example, from rough basement topography. Instead, the reflectors are attributed to tectonic and magmatic processes associated with the accretion of oceanic crust at the Mid-Atlantic Ridge. The upper crust shows variable reflectivity due to both dipping and sub-horizontal events. We interpret the dipping reflectors, which have been identified on both ridge-normal and ridge-parallel profiles, as sub-surface expressions of normal faults that formed at or near the Mid-Atlantic Ridge. There is no evidence that the faults are caused by loading of the oceanic crust by either the Cape Verde islands or their associated topographic swell. Some faults, however, can be traced into the overlying sediments suggesting they may have been re-activated since their formation at the ridge. The origin of the sub-horizontal reflectors is not as clear. We believe them to be boundaries of different igneous lithologies, such as that between basalts and gabbros. The lower crust is highly reflective in some areas, whereas in others only a few dipping and sub-horizontal reflectors are observed. Some of the dipping reflectors can be traced into the upper crust, suggesting they are also normal faults. Others, however, appear to be confined to the lower crust. The sub-horizontal, discontinuous, reflectors about 2.0–2.5 seconds two-way travel time below the top of oceanic basement are attributed to the Moho.
Introduction Seismic reflection profiling has proved a powerful tool for imaging the internal structure of oceanic crust. Studies at the relatively fast spreading East Pacific Rise (e.g. Ranero et al., 1997; Reston et al., 1999) and at the relatively slow spreading Mid-Atlantic Ridge (e.g. Mutter and Karson, 1992), for example, reveal clear images of intracrustal reflections, including sub-horizontal and dipping events in both the upper and lower part of the oceanic crust. In the eastern North Atlantic, Banda et al. (1992) imaged a variety of reflectors including sub-horizontal and dipping events within the igneous oceanic crust. Subsequently, Collie
Data Loading...
