Figure F4. Geochemical data for samples from the Mid-Atlantic Ridge. A. Na2O (upper panel = equator-70°N data; lower panel = 10°-20°N data) in basalts. B. Cr/(Cr + Al) in spinel (lower panel) and axial depth (upper panel). Low Na2O in A and high Cr/(Cr + Al) in B can be taken to indicate high degrees of partial melting. C. High La/Sm (upper panel = data from the equator to 70°N; lower panel = data from 10° to 20°N). D. High 207Pb/204Pb (upper panel) and high 87Sr/86Sr (lower panel). C and D are indicative of long-term enrichment of the mantle source in incompatible trace elements. All of these characteristics are observed along the Mid-Atlantic Ridge just south of the 15°20´N Fracture Zone (FZ). Basalt data compiled by Xia et al. (1991, 1992, unpubl. data) and Casey et al. (1992). Spinel data and bathymetry from Bonatti et al. (1992) and Sobolev et al. (1991, 1992a).

Figure F4. Geochemical data for samples from the Mid-Atlantic Ridge. A. Na₂O (upper panel = equator–70°N data; lower panel = 10°-20°N data) in basalts. B. Cr/(Cr + Al) in spinel (lower panel) and axial depth (upper panel). Low Na₂O in A and high Cr/(Cr + Al) in B can be taken to indicate high degrees of partial melting. C. High La/Sm (upper panel = data from the equator to 70°N; lower panel = data from 10° to 20°N). D. High ²⁰⁷Pb/²⁰⁴Pb (upper panel) and high ⁸⁷Sr/⁸⁶Sr (lower panel). C and D are indicative of long-term enrichment of the mantle source in incompatible trace elements. All of these characteristics are observed along the Mid-Atlantic Ridge just south of the 15°20´N Fracture Zone (FZ). Basalt data compiled by Xia et al. (1991, 1992, unpubl. data) and Casey et al. (1992). Spinel data and bathymetry from Bonatti et al. (1992) and Sobolev et al. (1991, 1992a).