Abstract
Santa Fe, Baltra and Espanola make up a geological subprovince in the central Galapagos; they are older than the other islands and their lavas are compositionally similar. When they emerged approx 3.9 m.y. ago, the three islands were in a tectonic setting similar to that of the young western and central Galapagos Island. Santa Fe was a volcanic centre on its emergence. A later horst along its central axis dominates its present morphology. It consists of evolved transitional lavas related not only by fractional crystallization. The trace-element variations may be explained by source heterogeneities, differing degrees of melting or open system magma chambers.