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In the eastern St. Francois Mountains of Missouri, a 1.48 Ga subvolcanic ring pluton, known as the Silvermine Granite, hosts swarms of dark, pillow-shaped enclaves exhibiting classical features of mafic melt globules trapped in granitic magma. The pillows formed by turbulent injection of near-liquidus mafic melt into a resident visco-plastic granitic magma. Exchange of crystals, fluids and ions between the two melts produced a hybrid tonalite-granite enclave series and modified host granite composition. Several lines of evidence suggest interaction between granitic melt that produced the granophyric cap of the pluton and basaltic melt that formed dikes in the area. Rapid cooling of the pillows re-melted the host creating back-veins in many enclaves. Mineral chemistry indicates the hybrid rocks have undergone extensive subsolidus re-equilibration. (C) 1999 Elsevier Science B.V. All rights reserved.