Dr. John Hogan, University of Missouri, Rolla Dr. Sheila Seaman, University of Massachusetts Igneous and Metamorphic Geology of Vinalhaven Island, Maine Robert A. Wiebe Department of Geosciences, Franklin and Marshall College, Lancaster, PA 17604-3003 David. He recognized the bimodal character of the complex, the widespread evidence for mixing between highly contrasted magmas, and described the mafic plutons as large, sheet-like masses with overlying granitic material that collected beneath a country rock roof. Some of these mafic bodies are well layered and fractionated.
Granitic bodies occur both as sheet-like masses and as subequant plutons with steep contacts.
The Vinalhaven plutonic complex appears to be perhaps the best exposed of these bimodal intrusions. The coastal outcrops are superb and show complex commingling and mixing relations between gabbroic, dioritic and granitic rocks near the base of the intrusion. Huge inclusions of metamorphosed country rock also occur near the base the pluton. Two main varieties of granite, both with mafic enclaves, are widely exposed and were easily sampled in coastal sections, vast quarries, and glaciated exposures inland. The highest levels of the intrusion cut into fresh, weakly deformed basaltic and rhyolitic volcanics that may be cogenetic with the plutonic rocks.