Baraboo Interval Quartzites in Iowa: Assessing the Provenance of the Washington County Quartzite

The Washington County Quartzite (WCQ) in southeastern Iowa is the southernmost occurrence of the Geon 17 “Baraboo Interval” quartzites in the Laurentian midcontinent region. Three drill holes encountered poorly sorted quartzite and phyllite, likely deposited in a braided fluvial or deltaic environment near the Laurentian continental margin on the Columbia supercontinent. 100 new LA-ICPMS detrital zircon U-Pb ages from the WCQ show a prominent 1.78 age peak, representing local Yavapai-aged basement, a secondary peak at 1.8-1.9 Ga representing a distal Penokean source, and a minor <2.5 Ga peak derived from distal sources in the Superior Province. Multidimensional scaling of other Baraboo Interval quartzites and potential sources show that the WCQ is indistinguishable from the lower interval of the Baraboo Quartzite. Cumulative distribution plots also reflect principal source areas derived by erosion of underlying Yavapai-aged crust and distally derived Penokean and older sources from the southern Superior Province. New whole rock geochemical data from the WCQ and potential granitic sources from northwestern Iowa are compared and show high (>80) chemical index of alteration (CIA) values, indicating similar weathering intensities to other Baraboo Interval localities. The WCQ likely serves as the down slope equivalent during initial Baraboo deposition.