GEOLOGY OF NEW EXPOSURES OF THE 1100 MA (KEWEENAWAN AGE) KALLANDER CREEK VOLCANICS IN IRON COUNTY, WISCONSIN

Bedrock belonging to the 1109-1094Ma old Kallander Creek Volcanics was exposed in several new quarries west of Hurley, Iron County, Wisconsin. The Kallander Creek Volcanics are otherwise poorly exposed in Wisconsin, so these new exposures allow a more detailed characterization of this unit. The series is about 6,500 m thick and consists of lava flows and pyroclastic rocks generally striking N55^oE and dipping steeply north. In a few places the rocks are overturned. The volcanic rocks described here are stratigraphically below a rhyolite body dated at 1099 Ma. Chemical analyses show that the newly exposed volcanic rocks range from trachybasalts through trachyandesites to rhyolites. These names are provisional, as significant Si, K and Na metasomatism may have occurred during burial metamorphism. Some of the rhyolites show, on both outcrop and thin section scale, exquisitely preserved devitrification features including lithophysae, spherulites and thunder eggs. Fluorite is locally common as a filling in the thunder eggs. Pillows occur in a few of the more mafic flows. The flows are often amygduloidal, with cavities filled with montmorillonitic clay, chalcedonic and macrocrystalline quartz, calcite, potassium feldspar, chlorite, laumontite and corrensite. There is a marked absence of prehnite, pumpellyite and epidote. This suggests a zeolite facies metamorphism with temperatures from 200- 250 degree C and zones of high fluid flow.