Abstract

In 1903 Daly published his classic report on Ascutney Mountain, Vermont, in which he concluded that this igneous complex was emplaced by piecemeal stoping. Since that time, however, many studies of igneous bodies have been made. Accordingly, it was deemed advisable to restudy Ascutney Mountain to see what light new information might shed on the method of intrusion. Three theories were found worthy of special consideration: forceful injection, piecemeal stoping, and cauldron subsidence.

Forceful injection will not satisfactorily explain the complex for several reasons: (1) The inequidimensional bodies of the complex have their longer axes athwart the regional structure. (2) The strike and dip of the country rock have not been disturbed. (3) The folds and linear features in the country rock are regional and plunge consistently to the north at low angles.

The authors believe that cauldron subsidence (ring-fracture stoping) will best explain the intrusion. Cauldron subsidence is suggested by: (1) The roughly elliptical outline of the main syenite stock of the complex; (2) the slender, arcuate screen of volcanic rocks on the west side of Ascutney Mountain; (3) the crescent‐shaped intrusion of Little Ascutney Mountain; and (4) the progressive, easterly shift of centers of successively younger intrusions.

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