Paleomagnetic and ground magnetic assessment of the Niagara fault system in northeastern Wisconsin and western Upper Peninsula Michigan

Paleomagnetic and ground magnetic techniques were utilized to study the structure in the area surrounding the Niagara fault, located in northern Wisconsin and the Upper Peninsula of Michigan, to unravel its plate tectonic history. There are four major results from this study.;Group two and three consists of the VGP's for rocks north of the NF. Group two represents the 1850-2000 Ma Paint River Group. These VGP's trend NW-SE and deviated at least 30;The second result is a ground magnetic survey map at 0.1 of a mile intervals. A major anomaly is traceable throughout Wisconsin and the upper peninsula of Michigan and is identified as the NF. The results redefine the location of the NF and a similar anomaly located north of and parallel to the NF.;The third result is a magnetic model of the area from selected survey lines. The models suggest three distinct terranes separated by the NF and the parallel anomaly. These terranes correspond to the three VGP groups.;First, a paleomagnetic database for the time period 1700-2100 Ma was obtained in an area that had no paleomagnetic data. Three virtual geomagnetic pole (VGP) groups are observed. The first group is the magmatic rocks south of the NF. The VGP's for the 1850-1950 Ma rocks south of the NF plot on the North American apparent polar wander path (APWP). The VGP's for the 1700-1850 Ma rocks deviate at least 35;Based on the above results, a plate tectonic history of the area is suggested. Southward subduction began along the NF at about forming the older magmatic rocks. The Paint River Group rocks are part of a suspect terrane and overly ocean crust. The NF represents the suture zone between the magmatic terrane and the suspect terrane. The Baraga Group rocks formed along the leading edge of the third terrane. The anomaly to the north of the NF represents the suture between the suspect terrane and the third terrane.