Gravitational Interpretation and Modelling of the South Mountain Batholith. Southern Nova Scotia.

Abstract

Much controversy surrounds the issue of the geometry of the South Mountain Batholith of southern Nova Scotia. Gravity data released by the Department of Energy, Mines and Resources within the last year has allowed a reinterpretation and clarification of previously obscure information. This study was undertaken to define more clearly the subsurface geology of the South Mountain Batholith using the latest information. Data were interpreted on the basis of rock types observed in the field, especially with regard to their specific gravity.

A Bouguer Anomaly contour map reveals the presence of a large gravimetric low from Yarmouth to Sheet Harbour, a distance of nearly 300 kilometers. The low can be subdivided into three relatively intense depression two of which have been previously mapped as adamellite (quartz monzonite). Preliminary reconnaissance and sampling were carried out during the summer of 1977 in the third area, a region southwest of Kejimkujik National Park. Petrographic and gravitational analysis indicate that it, too, is adamellite.

The density contrast between the adamellite (S. G. 2.63) and the remaining areas of granodiorite (S. G. 2.68) is sufficiently large to allow specific gravity to be used as one of the variables in testing an interpretive model of the dimensions of the batholith.

Using known or implied surface contacts, two and three dimensional models were tested. By altering the subsurface geometry of the models, it was possible to approximate the observed gravity with the gravity generated by the hypothetical model and thereby approach a possible shape for the batholith.

Keywords: Pages: 43 Supervisor: M. J. Keen