%0 Conference Proceedings %B Abstracts with Programs - Geological Society of America %D 2006 %T Fracture patterns across two terrane boundaries in eastern Massachusetts; implications for regional groundwater flow and recharge %A Stephen B Mabee %A Joseph P Kopera %K #StaffPubs %K Avalon Zone %K BEDROCK %K eastern Massachusetts %K faults %K foliation %K fractures %K ground water %K Hydrogeology 21 %K joints %K massachusetts %K Merrimack Belt %K movement %K observations %K patterns %K properties %K recharge %K shear zones %K style %K terranes %K United States %X 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 %B Abstracts with Programs - Geological Society of America %I Geological Society of America (GSA) : Boulder, CO, United States %C United States %V 38 %P 434 - 434 %8 2006/10/01/ %@ 00167592 %G eng %U https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_116563.htm %N 77 %! Abstracts with Programs - Geological Society of America %0 Conference Proceedings %B Geological Society of America Abstracts with Programs %D 2015 %T The Nashoba Terrane: A new tectonostratigraphy and shared structural styles with the Merrimack belt in Massachusetts %A Joseph P Kopera %K #StaffPubs %K acadian %K alleghenian %K amphibolite facies %K chlorite %K deformation %K eastern Massachusetts %K fabric %K folds %K Harvard Conglomerate %K Hudson %K merrimack %K Merrimack Belt %K nashoba %K Nashoba terrane %K nashua %K Nashua Trough %K pin hill %K Structural geology %K tectonic history %K tectonostratigraphy %X Recent STATEMAP-sponsored geologic mapping of several 7.5' 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. %B Geological Society of America Abstracts with Programs %7 3 %I Geological Society of America (GSA) : Boulder, CO, United States %C Northeastern Section - 50th Annual Meeting (23–25 March 2015), Bretton Woods, NH %V 47 %P 42 %8 03/2015 %G eng %U https://gsa.confex.com/gsa/2015NE/webprogram/Paper253009.html %0 Conference Proceedings %B Abstracts with Programs - Geological Society of America %D 2006 %T A new way of looking at, and mapping, bedrock; the hydrostructural domain map of the Ayer Quadrangle, northeastern Massachusetts %A Joseph P Kopera %A Stephen B Mabee %K #StaffPubs %K aquifers %K Ayer Quadrangle %K BEDROCK %K faults %K foliation %K fracture zones %K fractures %K ground water %K Hydrogeology 21 %K joints %K mapping %K massachusetts %K measurement %K Merrimack Belt %K movement %K Nashoba terrane %K northeastern Massachusetts %K observations %K orientation %K physical properties %K recharge %K shear zones %K Structural geology 16 %K style %K United States %X 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' 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. %B Abstracts with Programs - Geological Society of America %I Geological Society of America (GSA) : Boulder, CO, United States %C United States %V 38 %P 166 - 166 %8 2006/10/01/ %@ 00167592 %G eng %U https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_116561.htm %N 77 %! Abstracts with Programs - Geological Society of America