@proceedings {319,
	title = {The Nashoba Terrane: A new tectonostratigraphy and shared structural styles with the Merrimack belt in Massachusetts},
	volume = {47},
	year = {2015},
	month = {03/2015},
	pages = {42},
	publisher = {Geological Society of America (GSA) : Boulder, CO, United States},
	edition = {3},
	address = {Northeastern Section - 50th Annual Meeting (23{\textendash}25 March 2015), Bretton Woods, NH},
	abstract = {Recent STATEMAP-sponsored geologic mapping of several 7.5{\textquoteright} quadrangles in east-central Massachusetts describe a new tectonostratigraphy and structural history for migmatitic gneisses of the Cambro-Ordivician arc complex represented, in part, by the Nashoba Formation. While preserved sedimentary structures are absent, four discrete subunits can be mapped based on distinct lithologies. From structurally lowest to highest, they are: A felsic magnetite-bearing bt gneiss, a magnetite and silliminite rich mu-bearing bt paragneiss, gt-bearing sulfidic bt-gneisses interlayered with sulfidic schist, amphibolite, and marble, and a calc-silicate rich bt-gneiss.
The Nashoba terrane exhibits near-identical early and late styles of deformation to those in the adjacent Nashua sub-belt of the Merrimack terrane: Early amphibolite-facies isoclinal folding (D1) overprinted by tight upright folding (D2) and associated thrust faults define the map-scale geometry of tectonostratigraphic units between the two terranes. D2 occurred syn-peak upper amphibolite facies metamorphism in the Nashoba terrane while defined by retrograde greenschist facies fabrics in the Merrimack terrane. These are overprinted by outcrop-scale sinistral strike-slip motion (D3) in the Nashoba terrane progressively transitioning to late chlorite-grade NW-side down oblique extension (D4) exhibited in both terranes.
Correlation of the above sequence with existing geochronology, structural petrology, and tectonic studies by other workers in the area suggest that D1 in both terranes occurred prior to and/or during ~370 Ma Acadian orogenesis. Existing geochronology shows D2 fold and fabric development to be diachronous both within and across terranes: occurring both before and after ~363 Ma, with progressive development possibly as late as ~325 Ma, in the Nashoba terrane. D2 in the Nashua sub-belt of the Merrimack terrane occurs after ~330 Ma in the Carboniferous, as late at ~293 Ma in the Permian, during Alleghenian orogenesis. NW-side-down extension and associated rotation of M1 metamorphic isograds in the Merrimack Terrane, and exhumation of the Nashoba terrane, are generally accepted to have occurred during later stages of Alleghenian orogenesis in the Permian.
},
	keywords = {$\#$StaffPubs, acadian, alleghenian, amphibolite facies, chlorite, deformation, eastern Massachusetts, fabric, folds, Harvard Conglomerate, Hudson, merrimack, Merrimack Belt, nashoba, Nashoba terrane, nashua, Nashua Trough, pin hill, Structural geology, tectonic history, tectonostratigraphy},
	url = {https://gsa.confex.com/gsa/2015NE/webprogram/Paper253009.html},
	author = {Joseph P Kopera}
}
@Map {224,
	title = {Bedrock geologic map of the Marlborough quadrangle, Massachusetts},
	year = {2004},
	publisher = {Massachusetts Geological Survey},
	edition = {GM-06-01},
	keywords = {$\#$BedrockMaps, $\#$MGSPub, alaskite, amphibolite, Andover Granite, Ashland, Berlin, Bloody Bluff, Burlington Mylonite Zone, epidote, fault zone, gneiss, granite, granofels, Hope Valley Alaskite, Hopkinton, Hudson, Indian Head Hill, Lake Char, Malborough, Milford granite, Milham Reservoir, mylonite, Northborough, quartzite, schist, shear zone, Southborough, volcanic, Waltham Tectonic Melange, Westborough, Wolfpen Lens},
	author = {Joseph P Kopera and DiNitto, R.G. and Hepburn, J.C.}
}
@Map {318,
	title = {Preliminary Bedrock Geologic Map of the Hudson 7.5{\textquoteright} Quadrangle Worcester and Middlesex Counties, Massachusetts},
	year = {2014},
	month = {09/2014},
	publisher = {Massachusetts Geological Survey},
	edition = {14-01},
	abstract = {The Hudson quadrangle straddles the Clinton-Newbury Fault Zone (CNFZ), which separates low metamorphic grade Silurian turbiditic metasediments and Devonian plutons of the Nashua sub-belt (Robinson and Goldsmith, 1991) of the Merrimack Terrane to the northwest from the high-grade, migmatitic Cambro- Ordovician arc-complex of the Nashoba Terrane (Walsh et al., 2011; Loan 2011). This general area comprises the suture between the Gander and Avalon composite terranes of the Northern Appalachians (cf. Hibbard et al., 2006).

Metasedimentary rocks of the Merrimack Terrane are generally poorly exposed, with intrusives (Day, Dayp, SDgdt) and the Clinton-Newbury Fault zone and associated rocks (Ot) forming a prominent northeast trending ridge (Oak Hill in the town of Harvard) marking the eastern bordering slope of the Worcester Plateau (Emerson, 1917, p. 16). Elevation and local topographic relief gradually decreases and glacial cover increases to the east-southeast across the strike of the Nashoba Formation, which, locally, forms low-relief NE-trending strike-parallel ridges. These are cut by dramatic cross-strike cliffs and glacial spillway gorges developed along cross-strike joints and brittle faults, most notably on the western slopes of Rattlesnake Hill, southern slope of Powder House Hill and in Camp Resolute in Bolton in the west-central portion of the quadrangle, and the southern slope of the hill along the west side of Codman Hill Road in Harvard in the north-central portion of the quadrangle. The migmatitic ortho- and paragneisses, schists and associated metavolcanic rocks of the Nashoba Formation (_Sn) form a northeast striking belt underlying the southern two-thirds of the quadrangle. These are intruded by a variety of presumed Ordovician to Silurian intermediate intrusives (OSd, OSaqd) and Devonian or younger tonalites to granites (Dan, Danp, Dac).},
	keywords = {$\#$BedrockMaps, $\#$MGSPub, acton granite, ayer granite, Berlin, Bolton, Boxborough, Clinton-Newbury Fault, gneiss, Harvard, Harvard Conglomerate, Hudson, magnetite, Malborough, marble, migmatite, nashoba, Stow, tadmuck brook schist, Vaughn Hills},
	author = {Joseph P Kopera and W.R. Hansen}
}
@Map {226,
	title = {Preliminary bedrock geologic map of the Hudson quadrangle, Massachusetts},
	year = {2005},
	publisher = {Massachusetts Geological Survey},
	abstract = {<strong>This map has been superseded by MGS OFR 14-01: Preliminary Bedrock Geologic Map of the Hudson 7.5{\textquoteright} Quadrangle Worcester and Middlesex Counties, Massachusetts</strong>

	This map is an interim update to W.R. Hansen{\textquoteright}s 1956 Bedrock Geology of the Hudson and Maynard 7.5{\textquoteright} quadrangles (USGS Bulletin 1038). This draft version of the Bedrock Map of the Hudson Quadrangle (Kopera, 2005) has been removed pending the future release of an updated version. The above version should be considered outdated. If you would like a copy of this map, please contact Joseph Kopera at jkopera[at]geo[dot]geo[dot]umass[dot]edu</p>
},
	keywords = {$\#$BedrockMaps, $\#$MGSPub, acton granite, ayer granite, Berlin, Bolton, Boxborough, Clinton-Newbury Fault, gneiss, Harvard, Harvard Conglomerate, Hudson, magnetite, Malborough, marble, migmatite, nashoba, Stow, tadmuck brook schist, Vaughn Hills},
	author = {Joseph P Kopera and Hansen, W.R.}
}
