We relate this isotopic variability to the melt-mantle interaction process by which the troctolites generated.
Although the harzburgites have high Os (4000–2500 pg/g) and unradiogenic isotopic signatures ( 187Os/ 188Os = 0.128–0.124), the troctolites show variable Os (383–16 pg/g) and highly fractionated 187Os/ 188Os ratios (0.129–0.140), which correlate with mineral (e.g., olivine Fo) and bulk-rock (e.g., CaO, Ni, and Cu) compositions. Here we report Re-Os isotopes and platinum group element (PGE) compositions of residual mantle harzburgites (olivine forsterite, Fo 91–90) and troctolites (olivine Fo 89–87) likely produced by melt-rock reactions at the Central Indian Ridge crust-mantle boundary. Although this process may have a key role in defining the chemical signature of the oceanic crust, the effect of such melt-mantle interactions on the isotopic composition of the reacting melts has rarely been investigated.
It has been proposed that the oceanic crust-mantle boundary may partly form through interactions between melts and the shallow mantle.
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