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

维马断裂带是沿中大西洋海脊非洲隆起纬度的最北端的缓慢扩展、长错距的转换断层。断裂带的形态以平水充填的山谷和高出谷底2~4公里的改造平行的横向山脊为主。法国潜水器Nautile号最近的一系列潜水员发现，横脊的北侧暴露了洋壳的所有主要单位。这个项目试图了解横脊为何在毗邻的海底上方隆起，并通过研究横脊北侧暴露在洋壳中的一段来探索这种隆起的存在。该项目将首先用水扫描和LDGO的多频谱近底部城镇侧视声纳系统绘制一段200公里长的横向山脊。其目的是：(1)绘制发生垂直运动的断层网络图；(2)确定Vema横脊在成分和结构上是否对称；(3)绘制横脊上浅水石灰岩盖层的几何形状和范围；(4)地壳单元厚度和整个地壳剖面的沿走向变化；(5)成像地壳与上地幔和地壳单元之间的接触；(6)绘制出出于横脊的片状岩脉的倾角和走向图。

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.