Abstract

Field studies of five large differentiated lopolithic intrusions show that they possess many similar features. The bottoms of the intrusions are not parallel to the layering but in general dip more steeply toward the center. The bottoms of the intrusions are irregular and may deepen or shallow abruptly as much as several thousand feet. Any particular section of a lopolith reveals only a portion of the layers so that the average composition cannot be determined from outcrops. Corresponding patterns may be found in the layering of the Sudbury, Bushveld, and Great Dyke intrusions.

The lopoliths are interpreted as funnel-shaped in cross section with the most basic rocks in the lower portion of the funnel. The upper portion of the lopoliths may be similar to some batholithic granites, and the overlying roof rocks display mountain-folded structures in contrast to the gently warped underlying formations.

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