Current interpretation of the Keweenaw Fault associates the great thrust fault with a continental collision event called the Grenville Orogeny. That collision caused mountain ranges and massive uplifts and has been dated at 1040 to 1080 million years ago, with a peak of activity at 1060 million years.

Activity of the Keweenaw Fault had at least two profound effects. 1. It stopped the rifting of the Midcontinent Rift. If the collision hadn’t occurred, the rift might have continued and eventually become a ocean. and 2. It broke up the layers of lavas within the rift and formed the conduits for the native copper minerailzation events. Many of the smaller faults of the Keweenaw formed at this time and the stress associated with the Grenville likely motivated the fluid movements associated with copper and associated minerals.

The size or scale of the Keweenaw Fault is huge compared to most faults.  As the figure above shows, the lavas were pushed up above the level of the Jacobsville Sandstone.  This vertical distance is called the offset. Geologists have estimated the vertical offset of the Keweenaw Fault at about 5 km (3 miles). This offset may be the result of a large number of individual earthquake events, over a period of millions of years.

The actual geometry of broken pieces along the fault may be quite variable, as this cross sectional view (near Gay) shows.