Silicic Magma Chambers as Traps for Basaltic Magmas: The Cadillac Mountain Intrusive Complex, Mount Desert Island, Maine

The Cadillac Mountain intrusive complex, located on Mount Desert Island, Maine, provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma. The complex consists of three units: the Cadillac Mountain granite (CMG), the Somesville granite (SG), and gabbro-diorite (G-D). Basaltic magmas were emplaced before, during, and after the emplacement and crystallization of the granitic plutons, and the chambers of silicic magma acted as traps for basaltic magma. Basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro, while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma. The G-D unit (about 1.5 km thick) consists of interlayered gabbroic, dioritic, and granitic rocks. Although thin (