Geochemistry and petrology of the ancient Vygozero granitoids, southeastern Karelia

The ancient Vygozero tonalites (southeastern Karelia) were compared with wo rldwide Archean tonalites and trondhjemites (870 chemical analyses). The na tural tonalites, including the Vygozero granitoids, are lower in Al2O3 and CaO, and higher in MgO than partial melts (at the same SiO2 content) experi mentally derived from mafic rocks. The Nd and Sr isotopic signatures, toget her with trace and rare-earth element data on the Vygozero granitoids, are consistent with two-stage genetic model involving partial equilibrium melti ng of tonalitic gneisses at the second stage.