Composition of melt inclusions and age of zircons of plagiogneisses from the Kola Superdeep Borehole

A comprehensive study of melt inclusions and SHRIMP dating of zircons from trondhjemite gneisses of the sequence VIII from the Kola Superdeep Borehole has revealed presence of old primary magmatic crystals with age up to 2887+/-15 Ma. This is not consistent with the previous view, according to which the oldest zircons from the Archean Complex in SG-3 are products of granulite metamorphism. Primary magmatic zircons of early generation (from 2887 to 2842 Ma) formed in deep-seated magma chambers during partial crystallization of CO2-saturated trondhjemite estimates on duration of generation of tonalite-trondhjemite-granite melts through partial melting of mafic rocks.对科拉超深钻孔（Kola Superdeep Borehole）第八岩系奥长花岗片麻岩（trondhjemite gneisses）中的锆石熔体包裹体与SHRIMP定年（SHRIMP）开展的综合研究显示，该岩系中存在年龄可达2887±15 Ma的古老原生岩浆晶屑。这与此前的学术观点相悖：此前学界认为该钻孔SG-3孔太古宙杂岩（Archean Complex）中的最古老锆石为麻粒岩相变质作用的产物。本研究中，早期世代（2887 Ma至2842 Ma）的原生岩浆锆石形成于CO₂饱和奥长花岗岩（trondhjemite）发生部分结晶作用时的深源岩浆房内，同时估算了通过镁铁质岩石部分熔融形成英云闪长岩-奥长花岗岩-花岗岩（tonalite-trondhjemite-granite）熔体的持续时长。