RIFT MYSTERIES

Many years of study on the Midcontinent Rift System have provided a fairly good explanation for WHAT it is, WHERE it is, and WHEN it was. But there is still much to be learned about WHY and WHITHER. Both outcrops and drill holes have outlined the presence and lithologic character. Geophysical data have provided some of the physical relationships between the basalts and related sediments. Significant questions remain as to such features as “Why do the flanking basins seem to alternate in position?”, “Why are there shifts in direction and separations in the Rift trend?”, “What is the structural relationship between the Rift and the Nemaha Uplift?”, “Which Phanerozoic tectonic patterns can be related to the Rift?”. Some possible answers are available from the patterns in the prior history of accretion of the older containing basement. Variations in the intensity of gravity may indicate discrete volcanic basins and later zones of offset and wrench faulting across the Rift trend. Phanerozoic history may provide additional clues that respond to these and other questions.