Abyssal peridotites are exposed in the regions of ridge segmentation with reduced crustal thickness at slow spreading ridges (Dick, 1989; Cannat et al., 1995; Cannat, 1996). During Ocean Drilling Program (ODP) Leg 209, mantle peridotites exposed on the seafloor at the Mid-Atlantic Ridge from 14° to 16°N near the 15°20´ Fracture Zone were drilled. The primary aim of drilling was to characterize the spatial variation of mantle deformation patterns, residual peridotite composition, melt migration features, plutonic rocks, and hydrothermal alteration along axis (Kelemen, Kikawa, Miller, et al., 2004). Peridotite cores recovered during this leg were serpentinized harzburgite and dunite associated with gabbroic intrusion. Many residual peridotites indicate textural features of interaction with melt migrating along grain boundaries by diffused porous flow at the base of the thermal boundary layer (Seyler et al., 2007), whereas the presence of impregnated peridotites and hybrid troctolites at Sites 1271 and 1275 suggest extensive crystallization of intergranular melt at lower temperatures (Kelemen, Kikawa, Miller, et al., 2004). In this paper, we report chemical compositions for primary minerals in altered dunites and associated plutonic rocks recovered from Hole 1271B and discuss melt flow and reaction in the shallow upper mantle at the Mid-Atlantic Ridge near the 15°20´ Fracture Zone.