@proceedings {284, title = {Evidence for arsenic-mineralization in granitic basement rocks, Ayer Granodiorite, northeastern Massachusetts}, volume = {42}, year = {2010}, note = {Accession Number: 2010-100047; Conference Name: Geological Society of America, Northeastern Section, 45th annual meeting; Geological Society of America, Southeastern Section, 59th annual meeting; Baltimore, MD, United States; Conference Date: 20100314; Language: English; Coordinates: N420800N424400W0710200W0715300; Coden: GAAPBC; Collation: 1; Collation: 160; Publication Types: Abstract Only; Serial; Conference document; Updated Code: 201052; Monograph Title: Geological Society of America, Northeastern Section, 45th annual meeting; Geological Society of America, Southeastern Section, 59th annual meeting; joint meeting, abstracts volume; Monograph Author(s): Anonymous; Reviewed Item: Analytic}, month = {2010/03/01/}, pages = {160 - 160}, publisher = {Geological Society of America (GSA) : Boulder, CO, United States}, address = {United States}, abstract = {Core samples of the Ayer Granodiorite along the eastern margin of the Merrimack Belt in northeastern Massachusetts host a series of sulfide and oxide phases that resulted from interaction with sulfide-bearing meta-sedimentary host rocks. Euhedral arsenopyrite grains are found with ilmenite, apatite, and REE phosphates in zones that generally mimic the intersection between a gneissic fabric and a relict magmatic foliation. Arsenopyrite crystals are typically elongate with this lineation. Euhedral to subhedral pyrite crystals have also been observed, but are localized to areas without As-bearing phases. Micro-fractures that parallel either a steep NW-striking joint set or gently-dipping sheeting joints are commonly filled with interwoven calcite cements and As-bearing Fe-oxides. Surface coatings of major fracture sets are also characterized by Fe-As-rich rinds that host micron-scale sub-angular particles of quartz, feldspars, and phyllosilicates. Where micro-fractures are most concentrated, sulfide-bearing minerals are less common; however, subhedral to anhedral arsenopyrite grains do occur along some open micro-fractures. These crystals preserve lobate grain boundaries and are associated with As-bearing Fe-oxide-rich coatings along adjacent fractures. The presence of 1) pyrite, 2) arsenopyrite associated with phosphates, and 3) As-bearing fracture coatings suggests multiple stages of mineralization. We propose that intrusion-related fluid-rock interaction associated with heating of nearby sulfide-bearing schists of the Berwick Formation during Acadian orogenesis may have provided the necessary constituents for growth of sulfide phases in the Ayer. It appears that Late Devonian greenschist facies metamorphism and metasomatism led to mineralization that generated arsenopyrite and accompanying phosphates; however, the role of the cross-cutting Clinton Newbury Fault Zone as a conduit for hydrothermal fluids may also be important. Lower temperature As-bearing Fe-oxide and calcite coatings on open fractures surfaces may be associated with a change from lithostatic- to hydrostatic-pressures during post-glacial regional uplift. This mineralization appears to be synchronous with intense microfracturing that post-dates all other mineralization.}, keywords = {$\#$StaffPubs, acadian, arsenic, arsenides, arsenopyrite, Ayer Granodiorite, Berwick formation, fractured materials, geochemistry, granodiorites, Igneous and metamorphic petrology 05A, igneous rocks, lower Paleozoic, massachusetts, Merrimack Synclinorium, metals, metamorphic rocks, metamorphism, metasedimentary rocks, metasomatism, Middlesex County Massachusetts, migration of elements, mineralization, Mineralogy of non-silicates 01C, northeastern Massachusetts, orogeny, Paleozoic, plutonic rocks, pollutants, pollution, pyrite, sulfides, United States}, isbn = {00167592}, url = {https://gsa.confex.com/gsa/2010NE/finalprogram/abstract_169998.htm}, author = {Koteas, G. Christopher and Keskula, Anna J. and Stein, Carol L. and McTigue, David F. and Joseph P Kopera and Brandon, William C.} } @proceedings {351, title = {The influence of ductile structure and rheological heterogeneity on brittle structures as exhibited by Avalonian granites in southeastern Massachusetts}, volume = {40}, year = {2008}, month = {03/2008}, pages = {3}, publisher = {Geological Society of America (GSA) : Boulder, CO, United States}, edition = {2}, address = {Buffalo, NY}, abstract = {The orientation and geographic distribution of joints, veins, and brittle faults show a conspicuous correlation with the heterogeneous distribution of foliation and lineation intensity in Neo-Proterozoic granites and their deformed counterparts in southeastern Massachusetts. Field mapping and stereonet analysis of brittle and ductile structural data collected during 1:24,000-scale geologic mapping of the Milford quadrangle yielded the following general observations, which suggest that the ductile deformational history of this region appears to have strongly influenced the later development of brittle structures in the same rocks: The behavior of these fractures in relation to ductile structure have implications for rheological constraints on tectonic models of the post-Alleghenian core of the New England Appalachians, hydrogeologic models of regional fractured bedrock aquifers, and the interpretation of topographic lineaments.}, keywords = {$\#$StaffPubs, acadian, alleghenian, avalon, BEDROCK, dikes, foliation, fracture, fracture system, fracture trace, fractures, granite, granites, Hopkinton, joints, l-tectonites, lineaments, lineation, Milford, Upton}, url = {https://gsa.confex.com/gsa/2008NE/finalprogram/abstract_134899.htm}, author = {Joseph P Kopera} } @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 {219, title = {Preliminary bedrock geologic Map of the Milford quadrangle}, year = {2007}, publisher = {Massachusetts Geological Survey}, edition = {OFR-07-01}, abstract = {

Fracture Characterization Map is included as sheets 2 and 3. Water Resources data included as sheet 4.

GIS and metadata forthcoming

}, keywords = {$\#$BedrockMaps, $\#$FractureMaps, $\#$MGSPub, acadian, alaskite, alleghenian, amphibolite, antiform, Ashland, avalon, bedrock map, blackstone, fracture, GEOLOGIC MAP, gneiss, granite, Holliston, hopedale quartzite, Hopkinton, ironstone diorite, joints, l-tectonite, Mendon, MGS Publication, Milford, neoproterozoic, Northbridge, proterozoic, quarries, quartzite, Upton, Westborough}, author = {Joseph P Kopera and Shaw, C.E. and Fernandez, M.} } @Map {217, title = {Preliminary bedrock Geology of the Northern Portion of the Blackstone quadrangle, Massachusetts}, year = {2008}, publisher = {Massachusetts Geological Survey}, edition = {OFR-08-03}, abstract = {

This map is an interim progress report of mapping currently underway.

}, keywords = {$\#$BedrockMaps, $\#$MGSPub, acadian, alleghenian, avalon, bedrock map, Bellingham, blackstone, GEOLOGIC MAP, gneiss, granite, hopedale quartzite, ironstone diorite, Mendon, MGS Publication, Milford, Millville, neoproterozoic, Northbridge, proterozoic, quarries, Upton, Uxbridge}, url = {http://www.geo.umass.edu/stategeologist/}, author = {Joseph P Kopera and Shaw, C.J.} }