Dredge samples selected for study from the Vema, Romanche, and Chain fracture zones inclue serpentinized spinel lherzolites, ilmenite norites, oceanic tholeiites, and a teschenite. The serpentinized ultramafic rocks from the fracture zones are chemically and mineralogically similar to spinel lherzolites (or harzburgites) found as ultramafic tectonites or cumulates. The primary mineral assemblage is olivine (Fo89.3-91.6), orthopyroxene (En87.0-88.8) clinopyroxene (Wo38.4-49.0 En46.4-55.5 Fs4.0-6.1), and a spinel rich in Cr and Al. These rocks apparently respresent depleted upper mantle exposed at the base of the fracture zones or diapirically intruded along the freacture zones, or alternatively, ultramafic cumulates such as in ophiolite complexes. The TiO2-rich norites (TiO2 4.00-5.88 wt%) are iron-rich (FeO+0.9 Fe2O3 17.3-18.2 wt%) and compositionally resemble the late-stage Skaergaard rocks. Major minerals are plagioclase (An37-68), orthopyroxene (En58-70), clinopyroxene (Wo40-44 En15-17 Fs41-43), low-Mg ilmenite, and low-ti magnetite. Low K20 oceanic tholeiites from the central rift valley on the ridge are typical midocean ridge basalts. Megacrysts of plagioclase that include olivine grains are believed to be of cognate origin. The teschenite, which closely resembles the Black Jack sill teschenite, contains high-Ca titaniferous augite (Wo46-48 En23-31 FS15-31), plagiocase (An10-75), ilmenite, titaniferous magnetite, analcite, and zeolites. The diversity of rock types and the occurrence of alkalic basalt imply complex plutonic processes occurring within the fracture zones.