RECONNAISSANCE PALEOMAGNETIC STUDY OF THE ~1450 MA WOLF RIVER BATHOLITH, WISCONSIN

The Mesoproterozoic Wolf River composite batholith includes 11 plutons with compositions that range from rapakivi granite to adamellite with minor anorthosite,syenite and mangerite exposed over an area of 5000 km². Six igneous phases were analyzed using anisotropy of magnetic susceptibility (AMS), as a proxy for magmatic flow during intrusion, and five samples record a sub-horizontal magmatic flow in five different orientations; the Bowler anorthosite preserves no interpretable fabric. Paleopoles for this igneous suite preserve a wide variety of orientations with 2 reversed polarities and one sample, the Big Falls granite, with no interpretable result. We also analyzed the AMS fabric of two mylonites with igneous protoliths, the N70°W trending, steeply inclined Waupee greenstone in the Mountain Shear Zone and N40°W trending rhyolite at the Dells of the Eau Claire River and both samples preserve a clean fabric with Kmax plunging steeply in the plane of foliation. These sites, in addition to “Baraboo Interval” metasedimentary rocks at Rib Mountain (quartzite), Wausau (metagraywacke) and Baldwin (metaconglomerate), each preserve unique paleopole orientations including two reversals. There is no consistent AMS fabric or paleopole signature to any of the Wolf River phases or host rocks, suggesting post-intrusion deformation.