GEOLEX

Summary of Citation: St. Francois Mountains

Publication:
Kisvarsanyi, E.B., 1976, Missouri Precambrian revisited; Progress
   in studies of Precambrian geology, 1961-1976, IN Kisvarsanyi,
   E.B., ed., Studies in Precambrian Geology of Missouri, with
   a guide to selected parts of the St. Francois Mountains,
   Missouri: Missouri Geological Survey Report of Investigations,
   no. 61, p. 66-80, (Contribution to Precambrian geology, no.
   6).

Usage in Publication:
St. Francois Mountains Volcanic Supergroup

Modifications:	Geologic Province:	Dominant Lithology:
First used	Midcontinent region	Rhyolite Tuff

Summary:
Name adopted by Missouri Geological Survey for an assemblage of Precambrian volcanic rocks in St. Francois Mountains (presumably for which unit is named) located in southeast MO, Midcontinent region. Generalized column (p. 2 of volume) shows unit to include rhyolitic ash-flow tuffs, lava flows and bedded tuffs. [Constituent formations and groups of supergroup not specified; unit presumably includes formations defined by Berry, Jr., this volume, p. 81-90. Berry's proposed units include, from oldest to youngest, Shepherd Mountain, Cedar Bluff, and Pond Ridge Rhyolites; Buck Mountain Shut-ins Formation; Ironton, Lindsey Mountain, Russell Mountain, Wildcat Mountain, Bell Mountain, Royal Gorge and Taum Sauk Rhyolites; Proffit Mountain Formation; Johnson Shut-ins Rhyolite; and Cope Hollow Formation]. Older than St. Francois Mountains Intrusive Suite (first used). [Same geographic names should not be used for different units]. Oldest Precambrian unit in study area. Precambrian Y [Middle Proterozoic] age.

Summary of Citation: St. Francois Mountains

Publication:
Kisvarsanyi, E.B., Hebrank, A.W. and Ryan, R.F., 1981, Guidebook
   to the geology and ore deposits of the St. Francois Mountains,
   Missouri: Missouri Division of Geology and Land Survey Report
   of Investigations, no. 67, 119 p., (Contribution to Precambrian
   Geology, no. 9)

Usage in Publication:
St. Francois Mountains Volcanic Supergroup

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Midcontinent region

Summary:
Consists of Butler Hill Group (rank raised) in lower part and Taum Sauk Group (new) [name preoccupied; name used for both group and formation within it] in upper part. Study area is in St. Francois Mountains, southeast MO, Midcontinent region. Nomenclature listed in table 1. [This unit is not to be confused with St. Francois Mountains Intrusive Suite, a unit consisting of hypabyssal and plutonic rocks in St. Francois Mountains. Same geographic name should not be used for different units.] Assigned Precambrian Y age.

Summary of Citation: St. Francois Mountains

Publication:
Kisvarsanyi, E.B., 1990, General features of the St. Francois
   and Spavinaw granite-rhyolite terranes and the Precambrian
   Metallogenic region of southeast Missouri, IN Pratt, W.P.,
   and Sims, P.K., eds., The Midcontinent of the United States;
   permissive terrane for an Olympic dam-type deposit?: U.S.
   Geological Survey Bulletin, 1932, p. 48-57

Usage in Publication:
St. Francois granite-rhyolite terrane*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Isotopic dating Overview	Midcontinent region

Summary:
Exposed in a 900-km2 region in St. Francois Mountains, at crest of Ozark dome in southeast MO, Midcontinent region. Includes St. Francois Mountains Volcanic Supergroup and St. Francois Mountains Intrusive Suite. [The same name should not be used for different units.] Though its boundaries are not well defined, data from more than 500 drill holes indicate that terrane underlies most of southeast MO having an inferred areal extent of at least 100,000 km2. U/Pb ages on zircons by other workers date age of crystallization of terrane at 1.48 Ga, but terrane includes younger (1.38 Ga) plutons. Consists of more than a dozen overlapping ring complexes, cauldron subsidence structures with ring volcanoes and ring plutons, and resurgent calderas with central plutons. Volcanic rocks of terrane are mainly rhyolite ash-flow tuffs; as much as 1700 m are preserved locally. Granitic rocks of terrane consist of subvolcanic granite massifs, ring intrusions, and central plutons. St. Francois formed as part of an extensional tectonic regime within or near the margin of the Proterozoic North American continent.