Pb-Sr-He isotope and trace element geochemistry of the Cape Verde Archipelago

摘要: Abstract New lead, strontium and helium isotopic data, together with trace element concentrations, have been determined for basalts from the Cape Verde archipelago (Central Atlantic). Isotopic chemical variations are observed at scale of lead to definition two distinct groupings, in keeping earlier studies. The Northern Islands (Santo Antao, Sao Vicente, Nicolau Sal) present Pb compositions below Hemisphere Reference Line (NHRL) (cf. Hart, 1984) , unradiogenic Sr relatively primitive 4He/3He ratios. In contrast, Southern (Fogo Santiago) display isotopes above NHRL, moderately radiogenic MORB-like signatures. We propose that dichotomy between results presence three isotopically components source basalts: (1) recycled ∼1.6-Ga oceanic crust (high 206Pb/204Pb, low 87Sr/86Sr high 4He/3He); (2) lower mantle material 3He); (3) subcontinental lithosphere (low ratios). signature reflects mixing mantle, which small proportions entrained depleted local upper added. Basalts Islands, however, require addition an enriched component thought be lithospheric instead mantle. may stem delamination subsequent incorporation into plume, or remnant just before opening Central Atlantic. reflect interaction additional component, is identified as crustal material.