@proceedings {316,
	title = {A structural framework for the Nashoba Terrane in eastern Massachusetts.},
	volume = {45},
	year = {2013},
	pages = {107},
	abstract = {The exhumation and tectonic significance of the migmatitic Cambro-Ordovician arc-complex of the Nashoba terrane, located between lower-grade rocks of the Avalon and Merrimack terranes in Massachusetts, has historically presented an enigma, in part, due to a lack of detailed analysis of internal structure. We propose a new terrane-scale structural model based on nearly a decade of detailed geologic mapping to provide a framework for future study. A subvertical NE-striking composite fabric (S (sub n/n-1) ) forms the dominant structural grain of the terrane. S (sub n) commonly deforms an older layer-parallel foliation (S (sub n-1) ) about meter- to kilometer-scale, upright to steeply inclined, NE- and SW-plunging, tight disharmonic folds (F (sub n) ). In the Nashoba Formation migmatites, S (sub n) commonly transposes a subhorizontal S (sub n-1) enveloping surface into spaced meter-scale subvertical shear bands that are absent in the dominantly metavolcanic Marlborough Formation. Fold axis-parallel mineral stretching and intersection lineations (L (sub n) ) are locally overprinted on S (sub n) by subhorizontal peak metamorphic to retrograde mineral lineations (L (sub n/n+1) ). Ambiguous D (sub n) kinematics in the NE transition SW along strike to top-to-NW normal fold vergence and drag along steep north-dipping S (sub n) axial planes and S (sub n) - S (sub n+1) shear bands. Later strain (S (sub n+1) - S (sub n+2) ) appears to be progressively partitioned at lower grade to pre-existing S (sub n) shear bands and discrete internal and terrane bounding fault zones which display early high-grade top-to-SE dextral or sinistral motion (S (sub n-1) - S (sub n) ) broadly overprinted by lower-grade top-NW movement (S (sub n+1) ). We propose a tentative tectonic history incorporating sparse existing geochronologic and petrologic studies: Top SW D (sub n-1) motion coeval with approximately 425 Ma sill-grade metamorphism and possible accretion. D (sub n) initiating syn approximately 395 Ma peak metamorphism with migmatite generation along S (sub n) and progressive bulk fabric development largely complete by the intrusion of the relatively undeformed approximately 349 Ma Indian Head Hill granite. Exhumation can be accommodated by well-documented syn-to-post D (sub n) regional sinistral motion combined with progressively lower grade top-NW extension along discrete structures continuing through deposition and deformation of presumed Carboniferous basin sediments along the terrane boundary.},
	keywords = {$\#$StaffPubs, Cambrian, eastern Massachusetts, exhumation, fabric, fault zones, faults, foliation, massachusetts, metamorphism, Nashoba terrane, Ordovician, Paleozoic, Structural geology, tectonics, United States},
	issn = {00167592},
	url = {https://gsa.confex.com/gsa/2013NE/webprogram/Paper215867.html},
	author = {Joseph P Kopera and Matthew A Massey}
}
@Map {222,
	title = {Preliminary bedrock geologic Map of the Palmer quadrangle, Massachusetts},
	year = {2008},
	publisher = {Massachusetts Geological Survey},
	edition = {OFR-08-02},
	keywords = {$\#$BedrockMaps, $\#$MGSPub, AMMONOOSUC, Belchertown, Belchertown pluton, Brimfield, Clough, Monson, Palmer, Ware, Warren},
	author = {Matthew A Massey}
}
@Map {251,
	title = {Progress map of the preliminary bedrock geologic map of the Billerica quadrangle, Massachusetts},
	year = {2011},
	publisher = {Massachusetts Geological Survey},
	edition = {OFR11-03},
	abstract = {<strong>This map also contains brittle fracture data as part of the GIS files.</strong>

This map is a progress report of bedrock geologic mapping currently underway in the Billerica quadrangle. It is a compilation of ongoing field mapping (Massey, this study) and previously published work in the area (Alvord, 1973, 1975; Jahns et al.1959).

The Billerica quadrangle is located approximately 20 miles northwest of Boston along Route 3, just south of Lowell, in northeastern Massachusetts, encompassing the northwestern most Nashoba terrane and it{\textquoteright}s boundary with the Merrimack belt (Figure 1). In the Billerica quadrangle, the Merrimack Belt consists of limited exposures of highly strained metasediments, or possibly orthoschist derived from reconstituted igne- ous protolith. The Clinton-Newbury fault zone separates the Merrimack Belt from multiply deformed, polymetamorphic biotite gneisses, migmatites, and amphibolites of the Nashoba terrane.},
	keywords = {$\#$BedrockMaps, $\#$FractureMaps, $\#$MGSPub, Bedford, Berwick formation, Billerica, Billerica Schist, Boxford formation, Carlisle, Chelmsford, Clinton-Newbury Fault Zone, Concord, fracture, gneiss, joints, Lowell, magnetite, migmatite, nashoba, schist, Spencer Brook Fault, tadmuck brook schist, Tewksbury},
	author = {Matthew A Massey}
}
