6. Myrmekite as a Clue to Metasomatism on a Plutonic Scale: Origin of Some Peraluminous Granites

In this presentation questions are raised about a melt-restite unmixing model proposed by Barton and Sidle (1994) for the myrmekite-bearing Waldoboro granite complex along the southeastern coast of Maine (USA). This complex consists mostly of granite/granodiorite gneiss and granite, but smaller masses of quartz diorite, aplite, pegmatite, leucogranite, tourmaline granite, and granite porphyry occur. A mylonite zone extends through the granite porphyry on the east side of the pluton and through wall rock consisting of mafic igneous rocks of the Benner Hill sequence. On the west side, the granite complex is bordered by paragneisses of the Bucksport Formation. The granite pluton is poorly exposed in an area covering >340 km 2 , but relationships between rock types are readily apparent in wave-cut shorelines south of Friendship and along other shorelines on islands and the mainland.