The silurian Cranberry Island volcanic series of Mt. Desert Island, Maine

Lubick, Naomi

'The primary intent of this project is to characterize the felsite and tuff units of the Cranberry Island Volcanic Series (CIVS) on Mount Desert Island petrographically and chemically in order to assess their relationships and possibly constrain mode of emplacement.' 'The Cranberry Island Volcanic Series [CIVS] is part of a volcanic terrain accreted to the North American continent during the Acadian Orogeny. The CIVS has been divided into three units (Gilman and Chapman, 1988), only two of which are considered in this study (the third unit occurs on Great and Little Cranberry Islands to the south of Mount Desert Island). The two units that crop out on Mount Desert Island are felsites and lithic tuffs which fall within the rhyolite and dacite fields of LeBas (1986).' 'The major element chemistry of the felsite and tuff units are similar, with SiO2 ranging from 67-75% and with Na20 (2.5-4.5%) generally in excess of K2o. Chemical similarities indicate a probable genetic relationship between the two. Embayed quartz crystal clasts are present in both felsites and tuffs. The tuff unit consists of both ash flow and air fall varieties, the latter sometimes appearing as a tuff breccia with clasts up to 1.5 m. Crystal clast density ranges from less than 5% to densely crystalline. The felsite appears in the field as a uniform, pink, very fine-grained granite. Micrographic textures of quartz in feldspar are present throughout the interior of the felsite. However, samples from the margin display a finer crystalline texture, possibly indicating a chilled contact with the tuffs. These textural relationships as well as field relationships indicate that the felsite intruded the tuffs. The volcanic unit has been dated to 424 Ma.' 'The CIVS is one unit in a coastal volcanic belt accreted to North America during the Acadian orogeny. Tentative correlation with other volcanics of the Northern Appalachians further indicate possible modes of emplacement and tectonic history. Possibilities include an Andean-type subduction and collision or a continental rift zone. One possible scenario is that the CIVS was a volcanic are on the margin of Avalon, later rigidly accreted.' /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/