Abstract

Aeromagnetic lineament study of an area roughly 1° square (115 kms NS by 100 kms EW) in southeastern Missouri demonstrates the presence of a cardinally-oriented (NS-EW) fracture pairset in basement rocks. More numerous, however, are northwest and northeast trending lineaments of nearly all strike directions. Missouri aeromagnetic lineaments thus exhibit a greater strike variety than those studied earlier by the author in other areas of North America. The possibility of one or more shearing events having occurred since their formation as pairsets is suggested. Another explanation is the existence of four separate northwest and northeast pairsets.

Aeromagnetic lineament directions parallel the directions of Precambrian diabase dikes, and the lineaments themselves coincide in several cases with faults in the overlying non-magnetic Paleozoic sediments and with the boundaries of Precambrian granitic plutons as defined by aeromagnetics. The latter correlation suggests that intruding granite masses stope out weaker rock types up to the edges of their bounding faults, while maintaining a roughly round or oval shape.

The pervasive nature of Precambrian basement fracturing is again demonstrated by this study, although it would not be possible to predicate the existence of orthogonal fracture pairsets in the basement from the Missouri data as it was from earlier aeromagnetic lineament studies (Gay, 1972, 1973).