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Abstract

Some eclogitic and ultrabasic inclusions, their separated minerals, host rocks, and related samples have been analyzed by mass-spectrometric isotope dilution for K, Rb, Sr, Ba and rare-earth elements (RE), and by other techniques for selected major elements. The results of these analyses, considered in terms of measured trace-element phenocryst-matrix partition-coefficients, suggest the following trace-element models. Many inclusions are contaminated with at least K, Rb and Ba. Some Kakanui eclogite phases were equilibrated with liquids similar in trace element concentrations to alkali basalt. Some Roberts Victor eclogite and garnet peridotite phases were in equilibrium with kimberlite. Salt Lake Crater eclogite might represent a low-calcium-pyroxene cumulate from alkali basalt. Some peridotites appear to have equilibrated with tholeiitic basalt; but some of these may have been subsequently metamorphosed. Alkali basalt peridotite nodules are not cumulates or residues directly related to their hosts; they might be contaminated metamorphic rocks.Ancillary conclusions are that kimberlite, carbonatite and nepheline-melilite basalt appear to constitute a quantized trace-element group. Rare-earth concentrations are perhaps the best criteria for distinguishing carbonatites from sedimentary carbonates. Roberts Victor omphacite can have high KRb and BaCe. Clinopyroxene/garnet rare-earth ratios tend to be uniform, as, to a lesser extent, do diopside/orthopyroxene rare-earth ratios for coexisting minerals. Mantle rocks appear to have very low Eu2+Eu3+ ratios; this might indicate oxidizing conditions. Alkali basalts approach uniformity in trace-element concentrations. Various degrees of partial fusion of garnet peridotite could account for the whole spectrum of rare-earth concentrations observed for basalts.