In samples only slightly affected by hydration, the alteration was essentially isochemical: where more intense, hydration was accompanied by the mobility of TiO2, Zr and the light rare-earth elements (LREE). The mobility of these reputedly immobile trace elements is influenced by texture and secondary mineral assemblages. Rodingitization was accompanied by still greater mobility.
A Nd isochron with an age of 2726 ± 98 Ma and eNd(T) = +2.5 is defined by whole-rock samples. Because the spread of Sm-Nd ratios is far greater than can be explained by magmatic processes, the age is interpreted as that of the main alteration event during or soon after emplacement. Scattered initial Sr isotopic ratios and eNd(T) (+3.6 to +0.7) provide evidence for several younger events.
The eNd(T) of magmatic clinopyroxene (~+3.8) is higher than that of mafic to felsic rocks and pyoxenes from the Abibiti belt (eNd(T) ~ +2.5). This result implies: (1) the komatiites exchanged Nd with surrounding rocks during water/rock interaction; (2) the isotopic composition of komatiites and their mantle source differed from that of the more common basalts of the Abitibi belt.
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