Mapping a Cross-Section through Oceanic Lithosphere Exposed by Vertical Tectonics at the Vema Fracture Zone

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The Vema fracture zone is the northernmost of the slow- spreading, long-offset transform faults along the Mid-Atlantic Ridge at the latitude of the bulge of Africa. The morphology of the fracture zone is dominated by a flat-flooded, sediment-filled valley and a transform-parallel transverse ridge that towers 2 to 4 km above the valley floor. A recent series of divers by the French submersible Nautile has shown that the northern flank of the transverse ridge exposes all of the principal units of the oceanic crust. This project seeks to understand why the transverse ridge has been uplifted above the adjoining seafloor, and to exploit the existence of this uplift by examining a section through the oceanic crust exposed on the northern flank of the transverse ridge. The project will begin by mapping a 200 km long section of the transverse ridge with Hydrosweep and with LDGO's multispectral near-bottom-town side-looking sonar system. The objectives are: (1) to map the network of faults along which vertical motion has occurred; (2) to determine whether Vema transverse ridge is symmetrical in composition and structure; (3) to map the geometry and extent of the shallow water limestone cap on the transverse ridge; (4) to along-strike variability in the thickness of crustal units, and the crustal section as a whole; (5) to image the contacts between crust and upper mantle and among crustal units; and (6) to map dip and strike of sheeted dikes outcropping in the transverse ridge.