@proceedings {296, title = {Fracture patterns across two terrane boundaries in eastern Massachusetts; implications for regional groundwater flow and recharge}, volume = {38}, year = {2006}, note = {Accession Number: 2010-054322; Conference Name: Geological Society of America, 2006 annual meeting; Philadelphia, PA, United States; Conference Date: 20061022; Language: English; Coden: GAAPBC; Collation: 1; Collation: 434; Publication Types: Abstract Only; Serial; Conference document; Updated Code: 201030; Monograph Title: Geological Society of America, 2006 annual meeting; Monograph Author(s): Anonymous; Reviewed Item: Analytic}, month = {2006/10/01/}, pages = {434 - 434}, publisher = {Geological Society of America (GSA) : Boulder, CO, United States}, address = {United States}, abstract = {The integration of structural data and field-based observations is becoming increasingly critical in understanding groundwater flow behavior and recharge potential. Over the past 3 years, the Office of the Massachusetts State Geologist (OMSG) has collected 8225 fracture measurements from 187 stations across 3 adjacent quadrangles as part of its bedrock geologic mapping program. These data provide a north-south transect across the Nashoba Terrane and its boundaries with the Merrimack Belt and Avalon Terranes in eastern Massachusetts. Areas with similar fracture patterns can be grouped into "hydrostructural domains" with distinct hydrogeologic properties. Within the above transect, hydrostructural domains were observed to closely correspond with bedrock lithology and ductile structure, and therefore, tectonic history. Such domains are commonly bounded by faults or intrusive contacts. Common features observed across all domains include a NE-striking regional foliation with corresponding NW-striking, steeply-dipping cross-joints. Strongly layered metasedimentary and metavolcanic rocks of the Merrimack Belt and the Marlborough Formation in the Nashoba Terrane tend to have the most pervasive and closely-spaced foliation-parallel fractures (FPF). Foliation intensity and FPF generally increases towards shear zones and regional fault systems, especially within granites and gneisses. The moderate to steeply dipping, well-developed FPF in these rocks provides a potentially excellent conduit for vertical recharge and a strong NE-trending regional anistropy that may control groundwater flow. Granitoidal rocks have very consistent NS-EW orthogonal networks of vertical fractures and subhorizontal sheeting joints, providing excellent potential for vertical recharge and near-surface lateral flow. Features such as small brittle faults, fracture zones, fold axes, and fracture sets distinct to each domain may dominate local groundwater flow and recharge. Abstract 116563 modified by 72.70.224.253 on 7-12-2006}, keywords = {$\#$StaffPubs, Avalon Zone, BEDROCK, eastern Massachusetts, faults, foliation, fractures, ground water, Hydrogeology 21, joints, massachusetts, Merrimack Belt, movement, observations, patterns, properties, recharge, shear zones, style, terranes, United States}, isbn = {00167592}, url = {https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_116563.htm}, author = {Stephen B Mabee and Joseph P Kopera} } @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 {267, title = {A new way of looking at, and mapping, bedrock; the hydrostructural domain map of the Ayer Quadrangle, northeastern Massachusetts}, volume = {38}, year = {2006}, note = {Accession Number: 2008-100620; Conference Name: Geological Society of America, 2006 annual meeting; Philadelphia, PA, United States; Conference Date: 20061022; Language: English; Coden: GAAPBC; Collation: 1; Collation: 166; Publication Types: Abstract Only; Serial; Conference document; Updated Code: 200816; Monograph Title: Geological Society of America, 2006 annual meeting; Monograph Author(s): Anonymous; Reviewed Item: Analytic}, month = {2006/10/01/}, pages = {166 - 166}, publisher = {Geological Society of America (GSA) : Boulder, CO, United States}, address = {United States}, abstract = {While traditional bedrock geologic maps contain valuable information, they commonly lack data on fractures and physical properties of the rock. The increased need for better understanding of groundwater behavior in bedrock aquifers has made this data critical. Hydrostructural domain maps reclassify bedrock based on fracture systems and physical properties that may have implications for groundwater flow and recharge. These maps are constructed from detailed field observations and measurements of 2000-3000 fractures from 60-70 stations across a 7.5{\textquoteright} quadrangle. Hydrostructural domains are displayed on the map as traditional lithologic units would be, with detailed descriptions and photos of the fracture characteristics and physical properties of each hydrostructural "unit". In the Ayer Quadrangle, such domains closely correspond with bedrock lithology and ductile structural history. Steeply dipping metasedimentary rocks of the Merrimack Belt have pervasive, closely spaced, throughgoing fractures developed parallel to foliation, and therefore provide an excellent potential for vertical recharge. Where these rocks are intensely cut by a strong subhorizontal cleavage, a parallel fracture set dominates providing an opportunity for lateral flow. Massive granites generally have a well developed, widely-spaced orthogonal network of fracture zones which may provide excellent local recharge. High-grade gneisses of the Nashoba Terrane have poorly developed fracture sets except near regional shear zones, where foliation parallel fractures and cross-joints may provide good vertical recharge and provide a strong northeast trending flow anisotropy. These maps are intended to provide a regional-scale information to assist in site-specific groundwater investigations. We believe that such maps are an example of how new types of geologic maps can, and must, be developed to address changing societal needs.}, keywords = {$\#$StaffPubs, aquifers, Ayer Quadrangle, BEDROCK, faults, foliation, fracture zones, fractures, ground water, Hydrogeology 21, joints, mapping, massachusetts, measurement, Merrimack Belt, movement, Nashoba terrane, northeastern Massachusetts, observations, orientation, physical properties, recharge, shear zones, Structural geology 16, style, United States}, isbn = {00167592}, url = {https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_116561.htm}, author = {Joseph P Kopera and Stephen B Mabee} } @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} } @article {305, title = {Influence of rock fabric on fracture attribute distribution and implications for groundwater flow in the Nashoba Terrane, eastern Massachusetts}, journal = {Journal of Structural Geology}, volume = {30}, year = {2008}, note = {Accession Number: 2009-050694; Language: English; Coden: JSGEDY; Collation: 14; Publication Types: Serial; Updated Code: 200928; Reviewed Item: Analytic}, month = {2008/04/01/}, pages = {464 - 477}, publisher = {Elsevier : Oxford, International}, address = {International}, abstract = {Attributes (i.e. trace-length, spacing, termination and orientation) of joints and foliation-parallel fractures (FPFs) are used to assess the influence of lithology and fabric on fracture type and distribution in metamorphic and igneous rocks of the Nashoba terrane, Massachusetts. Orientations of NE-SW and NW-SE trending joints are consistent throughout the region, whereas FPFs are sub-parallel to the axis of the terrane. Joint spacing generally decreases to the northeast across the terrane reflecting lithologic changes from metamorphic to igneous rock types. Although trace-length and spacing frequency distributions of both joints and FPFs are best described by lognormal functions, FPFs possess narrower fracture spacing than joints. Median fracture trace-lengths of all FPFs are comparable to those of all steep joints, but the median fracture spacing is half that of all steep joints. Trace-lengths of FPFs vary as a function of the degree of development of foliation. Fracture attributes and groundwater flow models suggest that FPFs may significantly increase fracture connectivity and potential for groundwater recharge. FPFs may account for as much as 30\% of flow in fracture networks suggesting that in addition to joints, FPFs play a significant role in groundwater hydraulics that may include imparting flow anisotropy on the groundwater system.}, keywords = {$\#$StaffPubs, foliation, fractures, ground water, Hydrogeology 21, joints, massachusetts, movement, Nashoba terrane, preferred orientation, statistical distribution, structural analysis, Structural geology, style, terranes, United States}, isbn = {01918141}, url = {http://www.sciencedirect.com/science/article/pii/S0191814107002362}, author = {Alex K Manda and Stephen B Mabee and Donald U Wise} }