The Precambrian volcanic stratigraphy and petrology of the Des Arc NE 7 1/2 minute quadrangle, south central St. Francois Mountains, Missouri

Author

Vernon Max Brown

Abstract

"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.

Advisor(s)

Hagni, Richard D.

Committee Member(s)

Grant, S. Kerry
Proctor, Paul Dean, 1918-1999
Carr, James R.
Kisvarsanyi, Geza

Department(s)

Geosciences and Geological and Petroleum Engineering

Degree Name

Ph. D. in Geology and Geophysics

Sponsor(s)

Geological Survey (U.S.)

Comments

Two maps on two folded pages in the back pocket of the dissertation are included here as supplementary material as well as in the pdf.

Publisher

University of Missouri--Rolla

Publication Date

Fall 1983

Pagination

xv, 191 pages, maps

Note about bibliography

Includes bibliographical references (pages 132-136).

Geographic Coverage

Iron County, Missouri
Madison County, Missouri

Time Period

Precambrian

Rights

© 1983 Vernon Max Brown, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Geology -- MissouriGeology, Stratigraphic -- PrecambrianVolcanic ash, tuff, etc. -- Missouri

Thesis Number

T 4849

Print OCLC #

11312032

Electronic OCLC #

944901894

Recommended Citation

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.
https://scholarsmine.mst.edu/doctoral_dissertations/1037