"The Precambrian volcanics in the Des Arc NE 7½ minute quadrangle are composed predominantly of rhyolitic ash-flow tuffs with minor rhyolitic, trachytic, and andesitic lavas, and basaltic dikes. Thirty-seven volcanic units were identified, mapped, and informally named. A minimum of 1,000 meters of volcanic section is present. The rhyolites consist of phenocrysts of albitized alkali feldspar, albitic plagioclase, quartz, opaques, and ferromagnesium relicts set in a devitrified and locally recrystallized felsitic matrix. Pumice and lithophysal structures are common in the ash flows.
Chemically, the rhyolites are quite similar. The potassium to sodium ratio in individual units, however, tends to vary widely due to post-eruptive processes.
The rhyolitic ash-flow tuffs represent caldera and central vent eruptives which developed in high level, 1 to 2 Kb, differentiating reservoirs. Alteration and lack of outcrops present severe problems in identifying and studying individual suites of evolved products.
Fracturing and faulting is both common and complex. The Roselle Lineament, a major crustal fracture system, was identified on outcrop as a wide chaotic breccia zone. The Lake Killarney Caldera, newly proposed from this investigation, occurs in the northern portion of this quadrangle and the southern half of the Lake Killarney quadrangle. The caldera is believed to be a non-resurgent structure with the Lake Killarney ash-flow tuff its principal eruptive"--Abstract, page ii.
Hagni, Richard D.
Grant, S. Kerry
Proctor, Paul Dean, 1918-1999
Carr, James R.
Geosciences and Geological and Petroleum Engineering
Ph. D. in Geology and Geophysics
Geological Survey (U.S.)
University of Missouri--Rolla
xv, 191 pages, maps
Iron County, Missouri
Madison County, Missouri
© 1983 Vernon Max Brown, All rights reserved.
Dissertation - Restricted Access
Geology -- Missouri
Geology, Stratigraphic -- Precambrian
Volcanic ash, tuff, etc. -- Missouri
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Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.http://merlin.lib.umsystem.edu/record=b2693226~S5
Brown, Vernon Max, "The Precambrian volcanic stratigraphy and petrology of the Des Arc NE 7 1/2 minute quadrangle, south central St. Francois Mountains, Missouri" (1983). Doctoral Dissertations. 1037.
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