St. Francois Research

Missouri State University Department of Geography, Geology, and Planning

Proterozoic Geology of the St. Francois Mountains,

Southeastern Missouri

Thomas G. Plymate

Since the late 1980’s, I have been involving some of the better Missouri State undergraduate geology majors in a long-term research project involving the Proterozoic igneous rocks exposed in the St. Francois Mountains of southeastern Missouri. We have been using feldspar structural state to unravel the igneous (crystallization) and post-igneous (metasomatic/hydrothermal alteration) history of this volcanic/plutonic complex. To date, this line of research has produced two full-length journal articles (Plymate, Daniel, and Cavaleri, 1992; Plymate, Kendall, Shepard, and Clark, 2001) and three presentations with published abstracts. A third journal article (Mathenia and Plymate) has recently been submitted.

My second line of research on the Proterozoic rocks of the St. Francois Mountains involves the xenocryst-bearing mafic dikes exposed in the Silvermines area. Undergraduate students of mine have studied the petrography and geochemistry of these unusual rocks and have presented results of those studies at annual meetings of the Missouri Academy of Science (Woolsey, Plymate, and Craig, 1993; Johnson, Plymate, and Craig, 1997). I am currently collaborating with a former student to produce x-ray element maps of some of these xenocrysts. As soon as those maps are available, we will submit an article summarizing all the data on these rocks for publication in Transactions of the Missouri Academy of Science.

Publications and Presentations from the St. Francois Mountains Project

Daniel, C.G., Plymate, T.G., and Cavaleri, M.E., 1989, Structural State of the K-feldspar in the Butler Hill–Breadtray Granite, St. Francois Mountains, Southeastern Missouri [abstr.], Geological Society of America Abstracts with Programs, v. 21(4), p. 9. (Presented at Geological Society of America North-central Section Meeting, Notre Dame, IN, April 20, 1989.)

Plymate, T.G., Daniel, C.G., and Cavaleri, M.E., 1992, Structural State of the K-feldspar in the Butler Hill–Breadtray Granite, St. Francois Mountains, Southeastern Missouri, Canadian Mineralogist, v. 30, p. 367-376.

Woolsey, A.M., Plymate, T.G., and Craig, M. M., 1993, Compositional Variation in K-Feldspar Xenocrysts in a Basaltic Dike: an Example of the Use of SEM X-ray Elemental Mapping in Igneous Petrology [abstr.], Transactions of the Missouri Academy of Science, v. 27. (Presented at Missouri Academy of Science Annual Meeting, Kansas City, MO, April 23, 1993.)

Shepard, L.M., Kendall, J., Clark, K.C., and Plymate, T.G., 1996, Structural State of the K-feldspar in the Rhyolitic Tuffs and Ring Pluton Granites of the St. Francois Mountains, Southeastern Missouri [abstr.], Transactions of the Missouri Academy of Science, v. 30, p. 128. (Presented at Missouri Academy of Science Annual Meeting, Springfield, MO, April 19, 1996.)

Johnson, A.W., Plymate, T.G., and Craig, M.M., 1997, Geochemical Analysis of an Unusual Xenocryst-bearing Basaltic Dike Exposed in the Silver Mine Area of the St. Francois Mountains, Southeastern Missouri [abstr.], Transactions of the Missouri Academy of Science, v. 31, p. 90. (Presented at Missouri Academy of Science Annual Meeting, Warrensburg, MO, April 18, 1997.)

Plymate, T.G., Kendall, J., Shepard, L.M., and Clark, K.C., 2001, Structural State of the K-feldspar in the Ring Plutons and Rhyolitic Ash-Flow Tuffs in the Butler Hill–Breadtray Caldera Complex, St. Francois Mountains, Southeastern Missouri, Canadian Mineralogist, v. 39, p. 73-83.

Mathenia, C.M. and Plymate, T.G., 2001, Structural State of K-feldspar in Granites of the Taum Sauk Caldera, St. Francois Mountains, Southeastern Missouri [abstr.], Transactions of the Missouri Academy of Science, v. 35, p. 73-74. (Presented at Missouri Academy of Science Annual Meeting, Joplin, MO, April 21, 2001.)

Mathenia, C.M. and Plymate, T.G., Structural State of K-feldspar in Granites of the Taum Sauk Caldera, St. Francois Mountains, Southeastern Missouri: Evidence for Pervasive Subsolidus Alteration of the St. Francois Mountains Complex, submitted to Transactions of the Missouri Academy of Science.

Plymate, T.G., Johnson, A.W., Woolsey, A.M., and Craig, M.M., The “Silver Mine Quartz Basalt”: an Unusual Xenocryst-bearing Basaltic Dike Exposed in the St. Francois Mountains, Southeastern Missouri, in preparation for Transactions of the Missouri Academy of Science.

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