The nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge 33–35°N: A Sr-Nd-Hf isotopic perspective

We present new Sr-Nd-Hf isotopic data on mid-ocean ridge basalts from two segments (OH-1, OH-3) between the Oceanographer and Hayes fracture zones at Mid-Atlantic Ridge 33–35°N to constrain nature origin of upper mantle heterogeneity beneath Ridge. Together with major trace elements (Niu et al., 2001), illustrate that sources these lavas comprise three components, i.e., a depleted high radiogenic Hf compositions (ADM), an incompatible elemental enriched component Sr un-radiogenic Nd-Hf (E-type I), element variably isotope (i.e., E-type II). The ADM I components may be understood as representing ancient melting residues metasomatic veins developed base thickening oceanic lithosphere, respectively. unique II is best explained recent geochemically mantle, probably associated Azores plume north. Taking together, we interpret E-MORB dominated OH-1 resulting relatively higher degree source composed matrix material, whereas N-MORB OH-3 lower primarily comprising components. Such petrological geochemical understanding explains contrast in crustal thickness, morphology tomography, Bouguer anomalies segments.