Missing Eu anomaly and Archean high-grade granites

Granites emplaced in low-grade (granite-greenstone) Archaean terrains of S India typically exhibit negative Eu anomalies. A complementary reservoir in the lower crust with a positive Eu anomaly was found in Archaean high-grade granites. Geochemical model studies indicate that Archaean low- and high-grade granites may represent residual liquid and cumulate, respectively, from fractional crystallization of a granite parent magma produced by partial melting of tonalitic rocks in the lower crust. Such melting may occur at the wave front of a CO₂-rich fluid that dehydrates the lower crust and produces granulites.-L.C.H.