Boninite primary magmas: Evidence from the Cape Vogel Peninsula,PNG |
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| Authors: | D A Walker W E Cameron |
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| Institution: | 1. Department of Geology, Australian National University, P.O. Box 4, 2601, Canberra, A.C.T., Australia
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| Abstract: | Boninites from Cape Vogel, PNG, are dominantly pyroxene-glass rocks, but many contain olivine, sometimes as refractory as Fo94. We derive a parental magma for this suite (in equilibrium with Fo94) which contains 20 wt.% MgO and is quartz-normative. This liquid is hydrous, and from petrographie evidence and whole rock H2O+ values, we estimate it to contain 2–3 wt.% H2O. These data suggest olivine fractionation and primary magmatic water are important in boninite genesis, but both are often obscured by later alteration. The derived parental magma has probably formed at 1,250–1,300° C and low pressures (< ?10kB) and is similar to those which gave rise to olivine-clinoenstatite phyric boninites from New Caledonia and from Howqua, Australia, and possibly to a proposed parental magma for the Bushveld Complex. |
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