Assimilation in Petrography

the process of the interaction of magma with enclosing rock. As a result of assimilation, the magma completely or partially dissolves the matter of the enclosing rock and changes its own composition. According to the assimilation hypothesis, the melting of large foreign masses into the molten magma causes the diversity of magmatic rocks as well as determines the composition of the postmagmatic metalliferous solutions. Assimilation can also be a factor causing further differentiation of the magma. The favorable conditions for assimilation are a contrasting composition of the magma and the enclosing rock, the overheating of the magma, and the abundance of volatile components in it. The broad development of assimilation with the formation of gabbros and diorites is known in the marginal areas of granite intrusions which occur in limestone and basic effusive rock strata.