Altered basalt dikes from Hole 504B were partially melted at 1150°C and 1180°C to determine the composition of the first melts as oceanic Layer 2C is assimilated by a magma chamber. The partial melts are chemically similar to actinolite, the most abundant secondary mineral, but the melts are not simply melted actinolite. High TiO2, P2O5, and K2O abundances of the melts indicate that minor secondary minerals that are enriched in these elements also contribute to the melt. The incorporation of partial melts into a ridge-crest magma chamber may explain the local variability that is sometimes found in ocean ridge basalts that are not readily explained fractional crystallization or partial melting.

Supplement to: Fisk, Martin R; Johnson, Kevin T M; Alt, Jeffrey C (1995): Effect of assimilation of altered oceanic crust on magma chemistry: an experimental study. In: Erzinger, J; Becker, K; Dick, HJB; Stokking, LB (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 137, 43-51