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The sequence of Acadian deformations in central New Hampshire

By
J. Dykstra Eusden, Jr.
J. Dykstra Eusden, Jr.
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John B. Lyons
John B. Lyons
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Published:
January 01, 1993

The Central Maine Terrane (CMT) includes the rocks that extend northeasterly from Connecticut to Maine and from the Monroe Fault on the west to the Campbell Hill-Nonesuch River Fault Zone on the east. A four-phase sequence of Acadian regional deformation is recognized for the CMT cover sequence. D1, the earliest phase, is characterized by F1 nappes that have east or west vergence; the sense of vergence switches at the Central New Hampshire anticlinorium (CNHA). D1 is also characterized by early, rarely observed, low-angle and “blind” T1 thrust faults. The CNHA (or “dorsal zone”) is analogous to a “pop up” structure and is the likely root zone for both east- and west-verging Acadian D1 thrust-nappes. D2 is characterized by abundant F2 tight to isoclinal, inclined to recumbent folds with northeast-trending axes and east-southeast vergence. Most of these folds face downward, a reflection of D2 refolding the inverted limbs of D1 structures, and these structures are identifiable chiefly in eastern New Hampshire. F2 folds define a regional map-scale fold, the Lebanon antiformal syncline. During D3 broad, open, upright to inclined F3 folds with west- or northwest-trending axes were developed across the entire belt. F3 map-scale syntaxial folds are well defined by the outcrop pattern of the metasedimentary rocks. D4, the last phase of deformation, is characterized by F4, tight to isoclinal, inclined folds with north-northeast-trending axes and east vergence and is restricted to the western part of the CMT. F4 folds refolded the earlier structures and significantly modify the map pattern, tightening some of the earlier major structures in the CMT, for example the Kearsarge-Central Maine synclinorium. D2 and D4 are similarly oriented but spatially and temporally distinct. Deformation phases D1 through D4 are geographically restricted. This uneven distribution of structures is critical to correlations of deformation sequences across the orogen. Any local sequence of deformation in the CMT of central New Hampshire will commonly have only three of the four regional phases preserved in outcrop.

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GSA Special Papers

The Acadian Orogeny: Recent Studies in New England, Maritime Canada, and the Autochthonous Foreland

David C. Roy
David C. Roy
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James W. Skehan
James W. Skehan
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Geological Society of America
Volume
275
ISBN print:
9780813722757
Publication date:
January 01, 1993

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