Emplacement of the Butler Hill Granite, a shallow pluton within the St. Francois Mountains batholith, southeastern Missouri

Hypothesis for the origin of convergent margin granitoids and Earth’s continental crust by thermal migration zone refining

“…Observations in some vertically accessible bodies support variations in mode and composition with depth. For instance, the tilted and differentially exposed Butler Hill granite (St. Francois mountains, MO) shows a gradational mode from K-spar rich granite at shallow depth to plagioclase-rich granites at greater depth (Sides, 1980), a zoning pattern mimicked by the Dinkey Creek pluton (Bateman, 1992). Although modal zoning is not prominent, the Tinemaha granodiorite (Sawka and Chappell, 1988) has a vertical zoning of REE, Th and U contents.…”

Structural State of K-Feldspar in the Felsic Volcanic Rocks and Ring Pluton Granites of the Butler Hill Caldera, St. Francois Mountains, Southeastern Missouri

“…Figure 4A shows the K-feldspar structural state parameter Z for our analyses, as well as those of Plymate et al (1992) [recalculated using the regression equations of Kroll & Ribbe (1987)], plotted versus elevation with respect to a surface dipping 10°, S68°W. This surface, arbitrarily anchored at sample site F4 of Plymate et al (1992), represents a plane of constant major-element geochemistry within the main exposure of the Butler Hill -Breadtray Granite, and has therefore been inferred to represent a plane that was originally horizontal during the crystallization of this subvolcanic massif (Sides 1980). It is clear from Figure 4A that the structural state of the K-feldspar throughout the entire Butler Hill Caldera complex is highly ordered and very nearly homogeneous, and that there is no significant variation with inferred depth of crystallization.…”

“…Clendenin et al (1989) attributed this tilting to movement along the Simms Mountain Fault, one of a series of northwest-striking transfer faults formed during Late Proterozoic -Early Cambrian rifting and subsequently reactivated during the Middle to Late Paleozoic uplift of the Ozark Dome. On the basis of variation in majorelement geochemistry, Sides (1980) inferred that the Butler Hill -Breadtray Granite has been tilted approximately 10° in the S68°W direction, exposing rocks that had crystallized at depths ranging from as great as 10 km along the northeastern edge of the exposure to as little as 1 to 2 km along the intrusive contact with the volcanic rocks to the southwest.…”

“…Following the terminology of Pratt et al (1979), these volcanic units include Quartz Latite (Ys), Grassy Mountain Ignimbrite (Yag), and Alkali Rhyolite (Yar). The center of the Butler Hill Caldera exposes the Butler Hill -Breadtray Granite (Ygh + Ygg), a large texturally, mineralogically, and chemically differentiated, highsilica granite body interpreted to have formed as a subvolcanic massif that crystallized beneath a cover of its own volcanic ejecta (Sides 1980). Forming an arcuate ring between the outcrop areas of the Butler HillBreadtray Granite and the surrounding volcanic units are a series of smaller, lower-silica, amphibole-bearing FIG. 1.…”

Geochemistry of subsurface Proterozoic rocks in the eastern Midcontinent of the United States: Further evidence for a within-plate tectonic setting

“…Outcrops of Precambrian rocks occur in the St. Francois Mountains of southeastern Missouri (Sides, 1980;Bickford et al, 1981;Cullers et al, 1981;Sides et al, 1981), the Wolf River batholith of central Wisconsin (Anderson and Cullers, 1978), and the fel sic plutons of southern Manitoulin Island (Van Schmus et al, 1975). Inliers of 1.76 Ga rhyolite and granite in south-central Wisconsin, previously included in the Penokean orogen (Smith, 1978), have mainly A-type chemical affinities and are now known to postdate the Penokean orogeny (Smith, 1983(Smith, , 1993.…”