Two Paleoproterozoic (Statherian) Siliciclastic Metasedimentary Sequences in Central Wisconsin: The End of the Penokean Orogeny and Cratonic Stabilization of the Southern Lake Superior Region
paleoproterozoic, wisconsin, sedimentation, U-Pb, 40Ar/39Ar
Statherian siliciclastic sedimentary rocks in the southern Lake Superior region are key to understanding the evolution and stabilization of Paleoproterozoic crust in the midcontinent. Deposited during an important period of significant crustal growth, controversy exists regarding the conditions of sandstone deposition and the relations between magmatism and sedimentation. In central Wisconsin, the Hamilton Mounds inlier, although restricted in areal extent, is significant in that it reveals the existence of two separate Statherian units: an 1800–1760Ma immature meta-arkose and a post-1760Ma Baraboo Interval supermature quartzite. The meta-arkose is crosscut by 1762Ma granite and contains abundant Penokean age detrital monazite grains. The younger quartzite contains detrital monazite as young as 1750Ma and was deposited unconformably upon these older units. All units experienced 1630Ma low-grade recrystallization and isotopic disturbance associated with the Mazatzal Orogeny. In addition, the supermature quartzite experienced K-metasomatism and brecciation at 1470Ma, ascribed to regional-scale hydrothermal alteration related to the influence of the nearby 1470Ma Wolf River batholith. Collectively, these data suggest an early Statherian episode of arkosic deposition and magmatism during Yavapai orogenesis, followed by a longer interval of deposition of supermature quartz arenite associated with crustal stabilization. The existence of two separate Statherian units reconciles apparent conflicts in depositional models and provides a greater understanding of the Paleoproterozoic evolution of the midcontinent.
Medaris, L G.; Van Schmus, W R.; Loofboro, J; Stonier, P J.; Dott, R H.; Holm, Daniel; and Xhang, X (2007). Two Paleoproterozoic (Statherian) Siliciclastic Metasedimentary Sequences in Central Wisconsin: The End of the Penokean Orogeny and Cratonic Stabilization of the Southern Lake Superior Region. Precambrian Research 157(1-4), 188-202. doi: 10.1016/J.PRECAMRES.2007.02.016 Retrieved from http://digitalcommons.kent.edu/geolpubs/168