ALONG-AXIS MAGMATIC OSCILLATIONS AND EXPOSURE OF ULTRAMAFIC ROCKS IN A 2ND-ORDER SEGMENT OF THE MID-ATLANTIC RIDGE (33-DEGREES-43'N TO 34-DEGREES-07'N)

New in situ observations on the Mid-Atlantic Ridge demonstrate that th e along-and across-axis volcano-tectonic variability within second-ord er segments is larger than commonly acknowledged. In our study area, t he segment center, far from being the place with present-day maximum v olcanic activity, is dominated by extensive sedimentary cover, fissuri ng, and faulting, Furthermore, the area of most recent magmatic activi ty is located away from the segment center in a region of greater dept h and thinner crust. Segment-tip magmatic oscillations are suggested b y the distribution of rock types at both segment ends, Serpentinized p eridotites and associated dolerites are exposed at the massifs located at the intersection with nontransform discontinuities (NTDs), whereas only basaltic rocks crop out on the nodal basin floors, We suggest th at the combination of low magmatic budget and extension taking place a t the NTDs during a segment retreat favors the uplift and exposure of ultramafic massifs.