Geochemistry, origin, and nature of metamorphic rocks of the Batomga granite-greenstone terrane (Aldan Shield)

Abstract

Two series of volcanic rocks with different petrochemical affinities—calcalkaline and komatiite- tholeiitic series—were identified as protoliths for the Early Proterozoic metamorphic rocks of the Batomga granite-greenstone terrane. The metavolcanic rocks of the calcalkaline series comprise metabasalts, meta� andesites, metadacites, and metarhyolites. The distribution of the trace element abundances in the felsic metavolcanic rocks is similar to that of the Archean grey gneisses from the platform basements, thus suggest� ing a similar petrological mechanism for the formation of their protoliths. The protoliths for the komatiite-tholeiitic metavolcanic rocks include komatiite and tholeiite basalts. The chemical behavior of the tholeiites tends to support the fractionation of primary highMg basaltic magmas in a transient magma chamber at low pressures. The variations in the Nb, Y, and Zr contents of the metatoleiites indicate the derivation of their parental magmas from a plumerelated source.