Paleozoic/Mesozoic strata of the United States continental interior contain arrays of steeply dipping faults and associated monoclinal forced folds. Though these Midcontinent fault-and-fold zones clearly were active in pulses during the Phanerozoic, we suggest that they initiated during episodes of Proterozoic extensional tectonism. Based on fault-trace orientation, we divide Midcontinent fault-and-fold zones into two sets—one trending N to NE and the other trending W to NW. These sets effectively break the upper crust into blocks that jostle with respect to each other in response to changes in stress state. Notably, many W- to NW-trending fault-and-fold zones link along strike to define semi-continuous NW-trending deformation corridors. One of these, the 200 km-wide Transamerican tectonic zone (TTZ), traces over 2,500 km from Idaho to South Carolina. Seismic events occur in association with fault-and-fold zones, presumably because the zones persist as crustal weaknesses and/or stress risers. Significantly, seismicity most frequently occurs where N- to NE-trending fault-and-fold zones cross the TTZ, suggesting that intracratonic strain in the United States currently concentrates at or near intersecting fault zones within this corridor.

First Page Preview

First page PDF preview
You do not currently have access to this article.