Abstract
The Freetown layered complex, located on the western coast of Sierra Leone, is a rift-related tholeiitic intrusion associated with the Jurassic (∼193 Ma) opening of the Atlantic Ocean at midlatitude. The complex is ∼ 60 km long, 14 km wide, and 7 km thick along a major E-W traverse extending from Waterloo to York. Gravity data and dips of laminations in the layered rocks suggest that the intrusive complex is lopolithic in shape, with some parts presently being submarine. The exposed rocks consist of a rhythmically layered sequence of troctolite, olivine gabbro, gabbronorite, gabbro, and anorthosite. The complex has been divided into four zones delineated by (1) topographic expression, whereby the base of each zone forms a scarp, and the top forms dip slopes and strike valleys; and (2) cyclical repetition of rock types (Wells, 1962). A new detailed stratigraphic section along the Waterloo-York traverse is presented, in which Zone 3 is subdivided into an upper 2000-m-thick anorthosite-gabbro interval and a ...
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