PETROGRAPHY AND GEOCHEMISTRY OF MAFIC DIKES, WESTERN MAINE

Mafic dikes are observed throughout western and southwestern Maine intruding the igneous and metamorphic rocks that outcrop in this area of high-grade metamorphism. They intrude the 382 Ma Songo granodiorite, the 296 Ma Sebago granite, and are also observed intruding pegmatite bodies of this area as well as the metamorphic country rocks. Due to limited exposure, apart from pegmatite and granite quarries, it is unclear whether they comprise one suite of dikes or multiple dike series. Their source is also problematic, and therefore the focus of this study is to examine the petrography and geochemistry of these dikes to pinpoint their origin.

The dikes are predominantly aphryic basalt and coarser grained diabase, though some intermediate varieties also occur. They display distinct chilled margins with their host rocks and range in thickness from a few cms to 5m across. Typically they trend N – S or NE – SW and they are most commonly vertically inclined, although some are steeply dipping. When observed intruding the granitic rocks of the area they have been emplaced along the existing fracture pattern in these host rocks.

Possible sources for these mafic dikes include the Central Atlantic Magmatic Province, the White Mountain Magma Series or minor intrusive bodies such as the Rattlesnake Mt. stock, which intrudes the Sebago granite. Investigating the geochemical signature of these mafic intrusions will enable a more definitive assignment to one of these possible sources.