Abstract

We propose a new model to explain the geometric and petrologic characteristics of a large gabbro-syenite complex in the southern Appalachian Piedmont, based on reinterpretation of available gravity, magnetic, and petrologic data. In our interpretation the complex is composed of vertically stacked, tabular plutons, and the exposed intrusive rocks are underlain by a much larger body, vertically separated by 1-1.5 km. Our model provides a possible explanation for the perplexing absence from the Concord complex of rock types intermediate to syenite and gabbro in the fractionation sequence. Fractionation occurred in the deeper magma chamber, which was episodically tapped to produce syenite and gabbro at higher levels.

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