Mechanisms of magmatic assimilation at a marble contact, northern Haiti

Abstract

The unusually large Meme-Casseus and Bassin assimilation zones surround marble blocks in the 66 m.y.-old, epizonal Terre-Neuve quartz monzonite of northern Haiti. The Meme-Casseus zone, which contains syenodiorite, granodiorite, and minor nepheline syenite, occupies more volume than did the marble block. Therefore, dispersal, as well as addition, of material was required to form the contaminated zones. Mechanisms of addition of material to a magma can include congruent or incongruent melting of wall rock at normal or depressed melting points followed by solution of the melted material, or solution of solid rock by the magma. At the Meme-Casseus zone, minor melting may have occurred, but solution of solid marble was the dominant addition mechanism. Dispersal can take place by diffusion, crystal sinking, or convection, and at Meme-Casseus dispersal was caused largely by convection. The relation of addition to dispersal at the Meme-Casseus assimilation zone suggests that the formation of large assimilation zones is controlled by the mechanism of dispersal of material.