Melting in the oceanic upper mantle: An ion microprobe study of diopsides in abyssal peridotites

摘要: A systematic study of rare earth and other trace elements in discrete diopsides from residual abyssal peridotites sampled 5000 km ocean ridge demonstrates that they are the residues variable degrees melting garnet spinel peridotite fields. Further, data clearly demonstrate near-fractional melting, not batch typical basalt can evolve aggregated fractional melts. Ion microprobe analyses fracture zones along America-Antarctica Southwest Indian ridges reveal ubiquitous extreme fractionation (REE) ([Ce/Yb]n = 0.002–0.05); depletion Ti (300–1600 ppm), Zr (0.1–10 Sr ppm); relative to (Ti/Zr 250–4000). decrease with decreasing modal cpx peridotites, samples dredged near hotspots more depleted incompatible than those away hotspots, consistent higher upper mantle former. All studied exhibit marked negative anomalies REE. Incompatible element concentrations clinopyroxenes well modeled by repeated segregation ≤0.1% increments a total 5–25% process very close Rayleigh (fractional) melting; LREE-depleted source cannot account for observed peridotites. The shapes some REE patterns initiated within stability field. Trace calculated integrated liquids approximate composition primitive floor basalts, postsegregation aggregation small increment melts produced over depth interval.