DETRITAL ZIRCON PROVENANCE OF THE CAMBRIAN MT. SIMON SANDSTONE IN IOWA, USA: INSIGHTS FROM THE WESTERN END OF THE UPPER MISSISSIPPI VALLEY EPEIRIC RAMP

The Cambrian Mt. Simon Sandstone occurs throughout the Laurentian midcontinent, where it is exposed in Minnesota, Wisconsin, Michigan (Munising Formation), and Missouri (Lamotte Sandstone), and in the subsurface of Illinois, Iowa, Indiana, Michigan, Missouri, Ohio, Nebraska and western Ontario, Canada. It unconformably overlies Archean and Proterozoic basement rocks. Here we present the first detrital zircon data (LA-ICPMS, s=4, z=787) of drill core from the Mt. Simon in Iowa. In east-central Iowa, the W.F. Flynn M-1 core (W23148) was sampled at a depth of 2314 ft, about 4 ft above the unconformity with the underlying Mesoproterozoic Washington Quartzite. The Flynn detrital zircon age spectrum is well mixed, with age peaks of 1140, 1390, 1680, and 1771 Ma. The Peterson #1 core (W11749) from north-central Iowa, was sampled at a depth of 2165 ft, about 3 ft above the unconformity with weathered basalt of the Midcontinent Rift. The detrital zircon age spectrum for this sample also is well mixed, with age peaks of 1140, 1380, 1420, 1680, 1760, and 1836 Ma. Both the Flynn and Peterson age spectra include zircons from the various source terranes known from the Iowa basement, including the Midcontinent Rift, Northeast Iowa Intrusive Complex, Midcontinent Granite Rhyolite, Mazatzal, and Yavapai terranes. The Peterson 1836 Ma age peak is interpreted to be derived from the Trans-Hudson terrane present along the Transcontinental Arch, and few distally derived Grenville (1300-1000 Ma) or Superior province (~2700 Ma) zircons are present. The Camp Quest D-7 core (W25498) in northwest Iowa was sampled at a depth of 1060 ft, about 2 ft above the unconformity with the underlying ~1840 Ma Le Mars gneiss. The detrital zircon age spectrum reveals a unimodal age peak of 1787 Ma. The Harris D-13 core (W27270), also of northwest Iowa, was sampled at a depth of 882 ft, about 30 ft above the unconformity with the underlying ~1780 Ma Harris granite. The detrital zircon age spectrum has a unimodal peak of ~1840 Ma. Both the Harris and Camp Quest age spectra reflect local sediment sourcing from Trans-Hudson and Yavapai rocks present along the Transcontinental Arch at the western end of the Upper Mississippi Valley Epeiric Ramp.