The significance of Rb-Sr glauconite ages, Bonneterre Formation, Missouri: Late Devonian-Early Mississippian brine migration in the midcontinent: A discussion
- Yale Univ., New Haven, CT (United States)
Stein and Kish (1991) believe the Rb-Sr isochron obtained for glauconites from the mineralized parts of the Bonneterre Formation at the Magmont Mine, Missouri yields a date that corresponds to the time of mineralization. They examine and reject the hypothesis that these data represent a fictitious isochron, that is, a linear array in [sup 87]Rb/[sup 86]Sr-[sup 87]Sr/[sup 86]Sr space that forms by mixing of two components and that does not provide information about the timing of the event that generated the array. A more detailed examination of the Rb/Sr data from throughout the Bonneterre Formation reveals the likelihood that the Magmont 'isochron' is the result of mixing and, as such, does not provide information regarding the age of mineralization. The evidence presented in this paper contradicts the claim of Stein and Kish (1991, 1985) that mixing cannot produce the linear array of data in [sup 87]Sr/[sup 86]Sr-[sup 87]Rb/[sup 86]Sr space observed from Magmont glauconites: on the contrary, the Magmont data appear to be an extension, at higher Sr and lower [sup 87]Sr/[sup 86]Sr, of a mixing trend evident in 25 of 27 of the glauconites of the region. Because the linear array of Magmont data in [sup 87]Rb/[sup 86]Sr-[sup 87]Sr/[sup 86]Sr space probably formed by mixing as part of a larger array from the region, rather than by complete isotopic homogenization of Sr, it is a fictitious isochron: the slope of the line principally reflects the original Paleozoic age of the glauconites and provides no information about the timing of the event that generated the array.
- OSTI ID:
- 6937566
- Journal Information:
- Journal of Geology; (United States), Journal Name: Journal of Geology; (United States) Vol. 100:5; ISSN JGEOAZ; ISSN 0022-1376
- Country of Publication:
- United States
- Language:
- English
Similar Records
The significance of Rb-Sr glauconite ages, Bonneterre Formation, Missouri; Late Devonian-Early Mississippian brine migration in the midcontinent
Rb-Sr, K-Ar, and /sup 40/Ar//sup 39/Ar systematics in Paleozoic glauconite from Mississippi Valley-type localities, and the dating of events during sediment diagenesis
Related Subjects
152003 -- Geothermal Data & Theory-- Rock-Water-Gas Interactions
58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
BRINES
CARBONIFEROUS PERIOD
CHEMISTRY
DEVELOPED COUNTRIES
DEVONIAN PERIOD
FEDERAL REGION VII
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOTHERMOMETERS
GEOTHERMOMETRY
HYDROTHERMAL ALTERATION
ISOTOPE DATING
ISOTOPES
LEAD ORES
MEASURING INSTRUMENTS
MICA
MINERALIZATION
MINERALS
MISSOURI
NORTH AMERICA
ORES
PALEOZOIC ERA
ROCK-FLUID INTERACTIONS
RUBIDIUM ISOTOPES
SILICATE MINERALS
STRONTIUM ISOTOPES
THERMOMETERS
USA
ZINC ORES