@conference {369, title = {Latest Paleozoic through Mesozoic faults in north-central Massachusetts and their correlations with New Hampshire}, booktitle = {Geological Society of America - Northeastern section}, year = {2016}, publisher = {Geological Society of America}, organization = {Geological Society of America}, address = {Albany, NY}, abstract = {

Several faults in south-central New Hampshire can be extended into Massachusetts (MA) as a result of detailed mapping in both states since publication of the MA state bedrock geologic map in 1983. Many of these faults delineate and/or cut Devonian metamorphic isograds in the Silurian Merrimack Belt in northern MA, and juxtapose chlorite-grade rocks in the Nashua sub-belt (NSB) between lithologically similar middle- to upper amphibolite-facies rocks on either side.

Recent mapping in the NSB, combined with previous studies, suggest it may represent a graben initially formed during latest Paleozoic transtension contemporaneous with formation of the Narragansett Basin in southeastern MA and RI. Mylonites along the Silver Hill-Wekepeke Fault (Robinson, 1981), bounding the western edge of the NSB, show east-side-down normal motion and west-side down normal motion along the Clinton-Newbury Fault Zone (CNFZ; Goldstein, 1994) which bounds the NSB{\textquoteright}s southeastern margin. A possible extension of the Flint Hill fault system (NH) forms the eastern edge of the NSB offsetting the CNFZ with normal west-side down motion near Ayer, MA. Late brittle normal faults in the NSB are abundant.\ Late, low-To, west-side-down shear zones in the Nashoba Terrane and similar rocks to the south may also be related to down-dropping of the NSB.

AFT ages were collected across north-central MA to constrain its late uplift history. A ~127 Ma AFT age in the NSB is discontinuous with AFT ages in the belts adjoining it, with ~182-144 Ma ages west across the Wekepeke fault and ~160-167 Ma east across the CNFZ. To the west, the brittle southern extension of the Pinnacle Fault in NH (Stodge Meadow Pond fault of Peterson, 1984) follows the western edge of the Fitchburg plutons in MA while a well-exposed west-side down brittle normal fault system, possibly the southward extension of the Campbell Hill Fault (NH), is developed along their eastern edge. AFT ages of ~144-136 Ma immediately west of the Pinnacle Fault in MA are discontinuous with ~117-115 Ma ages immediately to the east within the Fitchburg plutons. A single ~106 Ma age in the plutons west of the Campbell Hill Fault in MA is discontinuous with ~128-123 Ma ages to the east of it. The discontinuities amongst AFT ages across these faults suggest that they may have been active through the Cretaceous.

}, keywords = {$\#$Bibliography, $\#$StaffPubs, AFT, apatite, apatite fission track, brittle, Campbel Hill, Clinton Newbury, Cretaceous, extension, fault, fault zone, fault zones, faults, fission track, Fitchburg, Fitchburg Plutons, Flint Hill, I-290, Johnny Appleseed, Jurassic, merrimack, mesozoic, Nashua Trough, Normal Faults, Oakdale formation, Permian, Pinnacle, Rt 2, Sterling, Stodge Meadow Pond, Triassic, Wachusett, Wekepeke, Worcester Formation}, doi = {10.1130/abs/2016NE-272576}, url = {https://gsa.confex.com/gsa/2016NE/webprogram/Paper272576.html}, author = {Kopera J.P. and Roden-Tice, M.K. and Robert P Wintsch} } @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 {359, title = {Bedrock geologic map of the Ayer 7.5{\textquoteright} quadrangle, Worcester and Middlesex Counties, Massachusetts (2015)}, publisher = {Massachusetts Geological Survey}, edition = {15-01}, abstract = {

Editing and review are still underway. \ This map should be available in winter 2015/2016

}, keywords = {Ayer, ayer granite, Ayer Granodiorite, Ayer Quadrangle, Berwick, Campbell Hill Fault, chelmsford granite, Clinton Newbury Fault, Devens, Harvard Conglomerate, merrimack, Oakdale formation, pin hill, Shepley{\textquoteright}s Hill, Shirley Fault, tadmuck brook schist, Worcester Formation}, author = {Joseph P Kopera} } @Map {360, title = {Bedrock geologic map of the Ayer 7.5{\textquoteright} quadrangle, Worcester and Middlesex Counties, Massachusetts}, publisher = {Massachusetts Geological Survey}, edition = {15-01}, abstract = {

Editing and review are still underway. \ This map should be available in winter 2015/2016

}, keywords = {Ayer, ayer granite, Ayer Granodiorite, Ayer Quadrangle, Berwick, Campbell Hill Fault, chelmsford granite, Clinton Newbury Fault, Devens, Harvard Conglomerate, merrimack, Oakdale formation, pin hill, Shepley{\textquoteright}s Hill, Shirley Fault, tadmuck brook schist, Worcester Formation}, author = {Kopera J.P.} }