Southern termination of Butternut Hill fold and evaluation of the nappe model for the Chester dome, Vermont
- Geological Survey, Reston, VA (United States)
According to previous interpretations the Acadian Hill fold (Thompson, Ph.D. thesis 1950) is a major, 20 km long, north-plunging synformal digitation containing inverted Middle Proterozoic gneiss and cover rocks along the western flank of the Chester dome. It constitutes the principal evidence for inversion of rocks in the nappe model of the Chester dome. Reexamination of the southern closure reveals that it does not close in a north plunging synform but the contact between cover rock and Middle Proterozoic gneiss dips southwest and west in a series of well-exposed minor folds. Steeply plunging folds in the cover rocks are the result of Acadian refolding of the earlier steeply dipping Taconian schistosity, that passes through vertical on the nose of the fold. The hingelines of the Acadian folds are highly irregular, but commonly plunge at 60 to 90 degrees within the subvertical and west dipping Acadian axial surfaces. Rather than supporting northerly dips and subhorizontal axial surfaces, plunges of hingelines of interference folds and of intersection lineations indicate folding of steeply-dipping schistosity and contacts. The data therefore do not support the existence of subhorizontal recumbent folds prior to development of the Butternut Hill fold. Projections showing the Butternut Hill fold as a downward closing synformal S shaped'' digitation of Middle Proterozoic core gneisses and cover rocks are not supported by the data presented here, as it is Z shaped in profile and upward closing. In the present interpretation, the Butternut Hill fold is a simple antiformal structure, possibly developed on a pre-existing (Taconian) reclined fold, that originally plunged steeply southeast in the regional (Taconian) schistosity. These observations suggest that a reevaluation of the Acadian nappe model for the Chester and Athens domes is necessary.
- OSTI ID:
- 5807269
- Report Number(s):
- CONF-9303211-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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