Abstract

Two- and three-dimensional modeling of gravity data from the area north of Penobscot Bay in south-central Maine reveals that major granitic intrusive masses there are tabular in shape. Batholiths are less than 7 km thick on the average and have nearly vertical contacts. Smaller granitic bodies average less than 3 km thick.

Structural and contact metamorphic features of granite and surrounding rocks suggest that felsic masses of batholithic proportions were emplaced at a late stage in the tectonic history of the area. Model configurations combined with structural evidence indicate that the batholiths were probably intruded along faults.

Several previously unmapped felsic masses have been located and defined, mainly within the Passagassawakeag Gneiss. The largest of these is the Stricklen Ridge Granite, an igneous mass up to 3 km thick and 11 km long. The near-surface dip of the Passagassawakeag Gneiss contact northeast of the Mount Waldo batholith is calculated to be 45°N to 55°N on the basis of gravity evidence.

A sill-like tongue of high-density rocks related to the Bays-of-Maine complex has been postulated to extend under the Ellsworth Schist north from Mount Desert Island and approach the Lucerne batholith near its southeastern contact. The Lucerne Granite is bounded on the north by a low-density body, proposed to represent a distinctly earlier felsic intrusion, now covered by a thin veneer of Lucerne Granite.

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