Stratigraphy and Structure of the Boundary Mountain Anticlinorium in the Errol Quadrangle, New Hampshire–Maine

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Abstract
The Errol quadrangle, New Hampshire–Maine (44° 45′–45° N. lat., 71°–71° 15′ W. long.) is underlain by approximately 27,000 feet of stratified metamorphic rocks that form the core of the Boundary Mountain anticlinorium. Approximately 22,000 feet of these rocks are probably Cambrian and Ordovician, overlain unconformably in the northwest corner of the area by a Siluro-Devonian sequence. The metamorphic rocks were intruded by a batholith of hornblende-biotite granodiorite (Taconic or Acadian) and several stocks of biotite-muscovite adamellite (Acadian). The pre-Silurian stratified rocks, in which the metamorphic grade ranges from the biotite to the sillimanite zone, are divided into three thick formations (from oldest to youngest): the Cambro-Ordovician(?) Aziscohos, the Ordovician (?) Albee, and the Ordovician(?) Dixville Formations. Most of these rocks are metasedimentary, but important metavolcanic units are present in the Dixville Formation and in the Siluro-Devonian sequence. The Aziscohos Formation is tentatively correlated with the Stowe and Ottauquechee Formations of Vermont and with the Mansonville of the Eastern Townships, Quebec. The Albee is traceable along strike to the type Albee in western New Hampshire and is correlated with the lower part of the Moretown Formation of Vermont and the lower part of the Beauceville Formation of the Eastern Townships. The Dixville is correlated with the Partridge and Ammonoosuc Formations of northwestern New Hampshire, the Cram Hill and upper Moretown Formations of Vermont, and the upper Beauceville of the Eastern Townships. The Siluro-Devonian rocks are correlated, at least in part, with the Seboomook Slate of northwestern Maine and the Eastern Townships. The stratified rocks in general trend northeast to north, but a major fold, the Diamond Peaks anticline, dominates the eastern and northeastern part of the area. It is believed to plunge south or southwest. Minor folds and other b lineations throughout most of the area plunge steeply with a strong vertical maximum and are believed to have been formed during a second stage of deformation. Because of the angular unconformity beneath the Siluro-Devonian rocks, it is inferred that broad folding occurred during the Taconic disturbance, although the major orogeny was Acadian.

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