Episodic potassic alteration of Ordovician tuffs in the Upper Mississippi Valley
Tuffs of middle and late Ordovician age are altered to mixed-layer illite-smectite (I/S) and to K-feldspar in the Upper Mississippi Valley in northeast Iowa, southeast Minnesota, and southwest Wisconsin. Some and perhaps much of the I/S replaces previously feldspathized tuff, as shown by field and petrographic relationships. Samples for K-Ar dating were collected over a 200 km southeast-northwest traverse. Dates from authigenic K-feldspar are early Devonian and range from 397 +/- 13 to 406 +/- 18, averaging 400 m.y. in three samples, including a middle Ordovician tuff in Iowa and Minnesota and a late Ordovician tuff in Minnesota. Ages of illite layers in I/S are late Devonian and early Mississippian and range from 356 +/- 16 to 371 +/- 17, averaging 366 m.y. in 5 samples including 4 from two middle Ordovician tuffs in Minnesota and Iowa and the late Ordovician tuff in Minnesota. Oxygen-isotopic composition of the K-feldspar and I/S shows that the two minerals crystallized under different conditions and probably reflect introduction of waters of varying chemistry and temperature. K-feldspar very likely crystallized under higher temperatures and possibly lower salinity than the I/S. Introduction of these pore waters may have been caused by groundwater movements resulting from recharge in distal areas undergoing tectonic uplift. K-feldspar alteration was concurrent with early Devonian uplift on the Northeast Missouri Arch and possibly the Transcontinental Arch. Age of the illite layers corresponds to movements on the Sangamon Arch and possibly the Wisconsin Arch.
- Research Organization:
- Case Western Reserve Univ., Cleveland, OH (USA)
- OSTI ID:
- 6320437
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
Similar Records
Potassium metasomatism and diffusion in Cretaceous K-bentonites from the disturbed belt, northwestern Montana and in the Middle Devonian Tioga K-bentonite, eastern USA
Age of K-feldspar authigenesis in Lower Paleozoic and uppermost Precambrian rocks of the Mississippi Valley area
Related Subjects
IOWA
TUFF
MINNESOTA
HYDROTHERMAL ALTERATION
WISCONSIN
CATAGENESIS
DIAGENESIS
FELDSPARS
GEOCHEMISTRY
ILLITE
ISOTOPE DATING
ORDOVICIAN PERIOD
OXYGEN ISOTOPES
PETROGRAPHY
QUANTITATIVE CHEMICAL ANALYSIS
SMECTITE
AGE ESTIMATION
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CHEMICAL ANALYSIS
CHEMISTRY
CLAYS
FEDERAL REGION V
FEDERAL REGION VII
GEOLOGIC AGES
ISOTOPES
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PALEOZOIC ERA
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
USA
580100* - Geology & Hydrology- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)