The South Atlantic Ridge Segmentation Between The Ascension And Bode Verde Fracture Zones

Analysis of bathymetry and gravity data reveals the<br>morphostructure and the mantle Bouguer anomaly<br>(MBA) variation along the ridge axis between the<br>Ascension and Bode Verde Fracture Zones. These<br>fracture zones are first order ridge discontinuities,<br>which are superimposed by four second order<br>discontinuities and at least two main third order<br>discontinuities. Such discontinuities bound seven<br>individualised ridge segments with distinct<br>morphotectonic styles. Despite of this segmented<br>structural framework, two tectonic domains<br>encompass the lower order discontinuities. To the<br>south of the Ascension Fracture Zone and north of the<br>Bode Verde Fracture Zone the ridge axis shows a<br>deep median valley (> 3000 m), suggesting a domain<br>controlled by extensional processes. On the other<br>hand, the median valley is generally absent midway<br>between the two fracture zones. Instead, there occurs<br>a topographically high volcanic edifice shallower than<br>2000 m associated with several off-axis seamounts to<br>the east. The existence of such topographic anomaly<br>along the ridge crest should reflect a domain<br>controlled by intense magmatism and probably less<br>faulting. The MBA variation within the whole first<br>order segment agrees with this interpretation. The<br>crustal thickening associated to the anomalous<br>topographic high at segment centre is not necessarily<br>an indicative of a hotspot influence at ridge axis.