Comment-Reply Medaris-VanWyck Jour Geol 2005

DISCUSSION AND REPLYDetrital Zircon Ages from Early Proterozoic Quartzites, Wisconsin,Support Rapid Weathering and Deposition of MatureQuartz Arenites: A DiscussionL. G. Medaris Jr., B. S. Singer, R. H. Dott Jr., and C. M. JohnsonDepartment of Geology and Geophysics, University of Wisconsin–Madison, Madison, Wisconsin 53706, U.S.A.(e-mail: medaris@geology.wisc.edu)IntroductionQuartzites of diverse ages and characteristics are is a member of the post-Penokean, Geon 17 graniteimportant features of the Precambrian basement in and rhyolite suite in the Lake Superior region,the Lake Superior region. Among these, the super- while the Baraboo Quartzite is nonconformable onmature quartzites of the Baraboo interval, which post-Penokean granite (1752 15 Ma) and rhyolitewere deposited between 1750 and 1630 Ma, record (1754 44 Ma; Van Wyck 1995; Medaris et al.a major episode of extensive chemical weathering 2003). Such relations clearly preclude correlationand siliciclastic sedimentation on a tectonically of the older Hamilton Mounds Quartzite with thestable plate margin (Medaris et al. 2003). Van Wyck younger Baraboo Quartzite and prohibit its inclu-and Norman (2004) have provided a large data set sion in the interval (1750–1630 Ma).on the ages of detrital zircons from two Proterozoic Further distinction between the two quartzitesquartzites in central Wisconsin: the Baraboo is provided by differences in their detrital zirconQuartzite, from which the Baraboo ...