The Piermond allochthon revisited and redefined at its type locality

Timms, Nichokas E. (2004) The Piermond allochthon revisited and redefined at its type locality. Geological Society of America Bulletin, 116 (11-12). pp. 1392-1407.

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Regional lithostratigraphic and structural mapping of the Piermont allochthon of northwestern New England at its type locality indicates that the Foster Hill fault, the supposed sole thrust, is a stratigraphic boundary. Rather, the allochthon lies above the Bean Brook fault, covers a much smaller area than suggested previously, and is limited to the vicinity of Piermont, western New Hampshire. The allochthon, which primarily consists of rocks correlated with the Silurian age Rangeley Formation of Maine, has horizons of metamorphosed polymictic conglomerate at its base. Rocks directly below the allochthon are correlated with the metasedimentary, Ordovician-aged Albee Formation and contain abundant metamorphosed dykes and sills that do not cross the sole detachment of the allochthon. Analysis of macro- and mesoscale structures indicates local preservation of fold hinges and overprinting foliations oblique to and later than those previously described and has allowed the deformation history to be significantly extended by several events. Emplacement of the allochthon early in the deformation history at metamorphic conditions caused NW-SE elongation lineations of clasts in conglomerate at the base of the allochthon. The relict foliations and fold hinges are commonly preserved below the allochthon, suggesting that these rocks have had a more protracted deformation history relative to rocks in the allochthon. The new interpretation of the Piermont area provides a framework to build a more thorough tectonic history for this part of the New England Appalachians.

Item ID: 13883
Item Type: Article (Research - C1)
ISSN: 0016-7606
Keywords: New Hampshire; Acadian tectonics; Piermont allochthon; synmetamorphic detachment; metaconglomerate
Date Deposited: 17 Nov 2010 02:42
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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