Department or Program

Geology

Abstract

The Newry-Gilead region of western Maine is comprised of migmatized Silurian (?) metasedimentary rocks intruded by members of a Devonian (?) quartz diorite suite, Devonian to Permian (?) two mica granite, and widespread migmatites and pegmatites. The bedrock was remapped in 2013, with the goal of reevaluating the region’s stratigraphy and intrusive rocks, and to ultimately gain a more complete understanding of the region’s tectonic history largely influenced by the Salinic and Acadian orogenies. Eight metasedimentary units and two igneous units were mapped for this project. This study focused on the metasedimentary units, and a complimentary study on the petrography of the igneous units was conducted by Saebyul Choe (2014). The metasedimentary rocks from youngest to oldest (?) include the following units: Sgf, a biotite and/or calc-silicate granofels (Madrid Formation?); Ssqr, a rusty schist and quartzite (Smalls Formation?); Sqsc, quartzite and schist with calc-silicate pods (Perry Mountain Formation?); Ssq, a greyschist and quartzite with calc-silicate pods; Ssg, a greyschist; Ssr, a rusty weathering schist with calc-silicate pods; Ssqg, a biotite granofels; and Ssqm, grey schist and quartzite with calc-silicate pods. The five oldest units are interpreted to be correlative with the Rangeley Fm. The abundant calc-silicate pods may represent olisotromal features deposited in an active tectonic setting during the Salinic Orogeny. The mapped units here differ greatly from the current Bedrock Geologic Map of Maine, due to the reconnaissance nature of the previous mapping in the region. All of what was previously mapped as Devonian Littleton Formation in the study area has been redesignated as Silurian Rangeley Formation. Perry Mountain Formation was identified in the study area for the first time. Two periods of ductile deformation and two periods of metamorphism occurred during and after the Acadian Orogeny. D1 is the establishment of schistosity and rare early folding. Four D2 folds were mapped in the field, and map and thin-section folds were also present. The area is heavily migmatized, which is correlated with Acadian subduction. Mineral alterations and late stage growth are associated with the intrusion of the Sebago Pluton. Fractures in the region are associated with the northwest-southeast tensile stress of Mesozoic rifting. The findings from this thesis place the deposition of the majority of the rocks as in the Salinic Silurian Orogeney. The next three units were deposited after the Salinic, but before the deposition of the Littleton Formation at the onset of the Acadian Orogeney. This model has regional implications for Appalachian tectonics and suggests that further mapping is needed in surrounding areas.

Level of Access

Open Access

First Advisor

Dyk Eusden

Date of Graduation

5-2014

Degree Name

Bachelor of Arts

Number of Pages

41

Components of Thesis

2 pdf files

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