FIELD RELATIONSHIPS WITHIN MAFIC ENCLAVE SWARMS IN THE MOUNT PERKINS PLUTON, NORTHWESTERN ARIZONA
The mafic microgranular enclaves typically have lobate or crenulate, sharp, chilled margins, notably darker and finer-grained than their interiors. They clearly formed as mafic magma was emplaced into granitic magma that was only partially crystallized. In one well-exposed swarm composed predominantly of large enclaves of this type, the shapes and distribution of the enclaves indicate that they were emplaced as a dike and were not transported far after breaking apart.
Many enclaves in another swarm contain abundant globular quartzofeldspathic aggregates, including some that resemble amygdules and others that, in the field, appear texturally and compositionally identical to leucocratic host granite and may be magmatic ocelli. Perhaps the latter crystallized from residual silicic magma that was incorporated into, and incompletely mixed with, the mafic magma at depth. The ocelli are individual and coalesced spheroids ranging from a few mm to a few cm across, concentrated in parallel bands near chilled margins of enclaves. The enclaves (and the bands of ocelli) are randomly oriented in this swarm. The mafic magma in this case must have decompressed and cooled enough for vesiculation and/or unmixing to occur before being dismembered and transported by the granitic host magma as enclaves in a turbulent suspension.