Centimeter- To Meter-Scale Structural and Petrographic Variations in a 3-D Exposure in the Migmatite Granite Complex, Southern Maine
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Authors
Luther, Brandon D.
Solar, Gary S.
Tomascak, Paul B.
Issue Date
2015-04-10
Type
poster_presentation
Language
en_US
Keywords
Geology , Structure , Migmatite , Granite , Pluton , Maine
Alternative Title
Abstract
Migmatites are a meta-igneous rock which crystallized early in the stages of melt, capturing the process of anatexas, or partial melting. As part of a multi-disciplinary study of rocks in the Migmatite-Granite belt of the Northern Appalachians, we have documented variations at the cm- to m- scale of fabrics and geometry of granitic bodies in a large, 3-D exposure in W. Cumberland, ME. This exposure is new as the homeowners have removed glacial till from the property, re-exposing glacially polished 76m x 24m pavement adjacent to a 15m high cliff face. An exposure of this magnitude and detail is rare since it is in an area of low outcrop density. This provided a unique opportunity to study a large 3-D outcrop within the Migmatite-Granite Complex (MGC).
The outcrop is dominated by metasedimentary metatexite migmatite which includes two 3-m-wide concordant amphibolite layers. The fabric of the outcrop exhibits a NE-SW trend with moderate SE dips. This outcrop resembles the same fabric found in regional data, which was expected. Dextral shear is indicated by asymmetric trails around porphyroblasts, boudinage, and ptygmatic folds of stromatic migmatite. The fabric indicating the shear is found within leucosomes, granitic bodies within the migmatite, indicating younger deformation than migmatite formation; this is also consistent with regional MGC data. Migmatite layers are intruded by granitic rocks with grain sizes from coarse to pegmatitic. Observations of contacts indicate cm-scale bake zones, also indicating the granite intruded following the formation of migmatite. Granite bodies are generally cm- to m- thick 2-mica coarse-grained granite to pegmatite. Cm-scale, medium grained granitic dikes are located throughout the outcrup cutting all structures, consistent with other rocks found throughout the MGC.