Structure of Central and East-Central Vermont

Abstract

The formations of central and east-central Vermont are exposed as a series of parallel belts that strike nearly north. Most of the rocks dip steeply, and many are overturned. With one possible exception, there seem to be no major repetitions within the sequence, and the order of formations from west to east appears to be the same as the order of their deposition. The formations are dominantly schist or phyllite, with varying proportions of arenaceous material. One thin formation, the Shaw Mountain, contains quartz conglomerate, calcareous tuff, and crinoidal limestone. The third-from-highest formation, the Waits River, is very thick and contains a large proportion of calcareous beds. The distance from the base of the lowest formation to the top of the highest, measured normal to bedding, is more than 100,opo feet; this large apparent thickness is believed to be not very much greater than the original thickness.The metasediments have been intruded by granitic dikes and plutons, mafic dikes, and small ultramafic plu,¥>;~-principal stages of deformation are distinguished. During the earlier stage the rocks were folded, and a schistosity was developed nearly parallel to bedding. Throughout the area the minor folds of this stage indicate a consistent upward movement of rocks on the east with respect to those on the west. The folds plunge at low to moderately steep angles, typically northward. Phenomena associated with the later stage of deformation decrease in intensity both eastward and westward from the belt underlain by the calcareous Waits River formation. At a distance from this formation, the rocks have prominent slip cleavage, and the earlier schistosity is folded. The minor folds plunge moderately to steeply northward on the western side of the area and more gently northward on the eastern. As the Waits River formation is approached, slip cleavage passes gradually into a schistosity that obliterates the earlier schistosity, and the intensity of later folding mcreases. In both the eastern and the western parts of the area the later minor folds indicate that the rocks of the Waits River formation have moved upward with respect to the formations on either side.The central part of the belt underlain by the Waits River formation is marked by a huge arch, 10-20 miles across, whose axis is more or less parallel to the belt and plunges gently northward. This is shown to be an arch, not in bedding, but in the later schistosity and in the axial planes of large isoclinal folds that were formed during the later stage of deformation. The axial planes of three of these large isoclinal folds can be correlated across the crest of the cleavage arch at Strafford Village.

Tectonic studies of the Berkshire Massif, western Massachusetts, Connecticut, and Vermont

“…White and Jahns (1950) found a similar deformational sequence in east-central Vermont. Moore ( 1949) mapped the eastern third of the Brattleboro 15-minute quadrangle in his study of the Keene-Brattleboro area.…”

Deformation microstructures of Barre granite: An optical, Sem and Tem study

“…It intrudes discordantly through the lower Devonian Giles and Waits River Formations, which were metamorphosed to biotite grade and intensely deformed during the Acadian orogeny (White and Jahns, 1950;Albee, 1968), between 385 and 410 Ma B.P. (Zartman et al, 1970;Naylor, 1971;Pajari et al, 1974;Dafmeyer et al, 1982).…”

Reevaluation of the Piermont-Frontenac allochthon in the Upper Connecticut Valley: Restoration of a coherent Boundary Mountains-Bronson Hill stratigraphic sequence

“…Marland Billings (1935Billings ( , 1937, in his classic work in the Littleton-Moosilauke area of New Hampshire, defi ned the Ordovician, Silurian, and Lower Devonian stratigraphy of the New Hampshire sequence (White and Jahns, 1950), and Billings traced those units across several metamorphic zones. Billings, his students, and others subsequently mapped this stratigraphy through much of central New England, and it is the framework for most tectonic interpretations.…”