GEOCHEMISTRY OF BURIED MIDCONTINENT RIFT VOLCANIC ROCKS IN IOWA: DATA FROM WELL SAMPLES
K.E. Seifert and R.R. Anderson
The Geological Society of America
31st Annual North-Central Section Meeting
Madison, WI, May 1-2, 1997
Abstracts with Programs, 1997, v. 29, no. 4, p. 71
Well cores and cuttings from deep wells into Precambrian igneous rocks from five separate parts of the buried Midcontinent Rift System in Iowa have been analyzed for major and trace elements. A total of 21 samples, 9 cores and 12 cuttings, were analyzed for trace elements by instrumental neutron activation analysis (INAA) and 11 of these, 9 cores and 2 cuttings, were analyzed for major elements by inductively coupled plasma atomic emission spectroscopy (ICP-AES or ICP) analysis.
Incompatible trace element concentrations of the Iowa well samples, especially the relatively immobile rare earth elements, indicate most samples are basaltic in composition, although three samples appear andesitic in composition. Major element compositions and textures indicate that low-temperature weathering and/or high-temperature burial metamorphism effects are abundant and most samples are extensively oxidized and hydrated. A notable alteration feature is the almost total depletion of sodium, without an accompanying loss of other soluble elements, perhaps resulting from selective removal by solutions.