STUDIES OF THE PRECAMBRIAN GEOLOGY OF IOWA:
PART 2. THE MATLOCK KERATOPHYRE

by
K. E. Windom, K. E. Seifert, and R. R. Anderson

Journal of the Iowa Academy of Science, 1991, v. 98, no. 4, p. 178-181

ABSTRACT


Felsic pyroclastic rock occurs in the Precambrian basement in northwestern Iowa. This rock was recovered by drilling and originally logged as rhyolite; however it is severely depleted in K2O, Rb, Ba, Cs, and other mobile elements and is ore properly called keratophyre. The volcanic unit lies atop a layered mafic/ultramafic complex and contains xenoliths of gabbro apparently derived from the layered body. These xenoliths are severely altered and are composed of secondary hydrated and carbonated minerals. The gabbros are enriched in incompatible trace elements, whose abundance patterns complement those of the keratophyre. Trace element abundance patterns for the keratophyre suggest it was derived by partial melting in a subduction zone. The keratophyre is comparable to rhyolite exposed in Wisconsin in terms of age, stratigraphic position, and low-grade metamorphism, although it cannot be established whether or not they are related in any way.