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ST. FRANCOIS MOUNTAINS VOLCANIC SUPERGROUP

ST. FRANCOIS MOUNTAINS VOLCANIC SUPERGROUP (chiefly alkali rhyolitic ash - flow tuffs, lava flows, and bedded tuffs, with minor trachytes.
State Missouri
Name ST. FRANCOIS MOUNTAINS VOLCANIC SUPERGROUP
Geologic age Precambrian [Y]
Comments The St. Francois Mountains is a region of formerly extentive volcanic terrane comprising several calderas, cauldron subsidence structures, ring intrusions, and resurgent cauldrons. Three calderas are recognized: the Taum Sauk, the Butler Hill, and the Hawn Peak.
Primary rock type rhyolite
Secondary rock type trachyte
Other rock types
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, ash-flow)
Minor
Igneous > Volcanic > Felsic-volcanic > Trachyte (Pyroclastic, ash-flow)
Map references
Middendorf, M. A., and others, 2003, Geologic Map of Missouri: Missouri Geological Survey. Scale 1:500K
Unit references
Howe, W. B. and Koenig, 1961, The Stratigraphic Succession in Missouri: Missouri Geological Survey and Water Resources, Vol XL. 2nd Series.
Counties Carter - Iron - Madison - Reynolds - Saint Francois - Shannon - Washington - Wayne