ABSTRACT
Four categories of structural control have been identified that help explain the geometry and map distribution of late Cenozoic, range-bounding normal faults adjacent to the Yellowstone hotspot. Type I range-bounding faults are those that are influenced by the fabric (planar anisotropy) of adjacent rocks; Type II are those inherited from fault zones associated with the Middle Proterozoic Belt Basin; Type III are those that reactivate frontal and/or lateral ramps in older contractional structures; and Type IV are those defined by the limbs of older fault-propagation folds. Combinations of two or more of these types are common. These observations suggest that the distribution of late Cenozoic normal faults across the northern Rocky Mountain region generally lacks a direct correlation to an ideal stress/strain field resulting from mantle hotspot doming. Rather, structural inheritance from features that predate formation of the hotspot seems to play an important role in determining the geometry and orientation of these young normal faults.
