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

Abstract

Upper crustal Proterozoic rocks in the eastern Midcontinent of the UnitedStates are part of the Transcontinental Proterozoic province, a 3,000-km-long belt of mainly felsic igneous rocks that extends from western Ohio to southern Cali fornia. In the eastern Midcontinent the province consists mainly of epizonal to mesozonal granite and related rhyolite that were deposited on and emplaced within older Proterozoic rocks. New major and trace element geochemical analyses of fel sic and mafic igneous rocks in the eastern Midcontinent are presented to character ize the geologic and tectonic environment in which they formed. Felsic igneous rocks have mainly A-type chemical affinities and accumulated in a within-plate tectonic environment. Similarly, eastern Midcontinent basalts are continental within-plate tholeiites that display limited enrichment in large ion lithophile elements and light rare earth elements.The granite-rhyolite igneous suite implies magmatism associated with extension in Middle Proterozoic time. Subsequently, basaltic volcanism accompanied further extension during rifting and sedimentation. Prominent rifts include the midMichigan rift (southeast extension of the well-known Middle Proterozoic Keweenawan Midcontinent rift system), the Ft. Wayne rift, and the New Madrid rift complex (a Cambrian to possible Late Proterozoic structure that extends into the craton beneath the Mississippi embayment). Some rifts are floored by flood basalt or gabbro and are overlain by clastic sedimentary rock; others are filled only with clastic sedimentary rock. The mid-Michigan and the Ft. Wayne rifts are characterized by elongate arrays of positive magnetic and gravity anomalies, attesting to thick accu mulations of mafic igneous rocks. In contrast, because prominent potential field anomalies occur only along the margins of the New Madrid rift complex, this fea ture may contain mainly sedimentary rock and only minor basalt. The Middle Run structure in southwestern Ohio and adjacent Indiana is not associated with regional gravity or magnetic anomalies and is apparently filled with Middle or Late Protero zoic or younger sedimentary rock. Other prominent anomalies occur within the granite-rhyolite terrane: these include widespread, large (10-20 km diameter), high-amplitude (600-700 gamma) circular to elliptical positive magnetic anomalies that are associated with magnetite-series granite. Detailed magnetic studies of the Spavinaw, Oklahoma, granite reveal that the enhanced magnetization is attribut able to two generations of magnetite.

North America’s Midcontinent Rift: When rift met LIP

“…We suspect the remainder of the MCR behaved similarly but cannot confirm this for the buried west and east arms of the MCR because comparable data are not available. However, the available seismic data (Zhu and Brown, 1986;Chandler et al, 1989;Woelk and Hinze, 1991) and older petrological analysis from a few drillhole samples (Keller et al, 1982;Dickas et al, 1992;Walker and Misra, 1992;Cullers and Berendsen, 1993;Lidiak, 1996) show similarities to what is observed in the Lake Superior area.…”

Anorogenic Acid Volcanic rocks in the Kundal area of the Malani Igneous Suite, Northwestern India: geochemical and petrogenetic studies

“…Furthermore, the difference in Zr/Y and Zr/Nb values do not support the derivation of an acidic melt from basic magmas by fractional crystallization. Bickford and Anderson (1993) have proposed two contrasting tectonic environments for the Neoproterozoic granite-rhyolite provinces, an anorogenic, rift-related environment and an active continental margin (Lidaiak, 1996;Rivers and Corrigen, 2000;Karlstrom et al, 2001). An anorogenic, rift-related environment is more compatible with the apparent lack of compressive deformation or moderate to high-grade metamorphism throughout the granite-rhyolite provinces (Van Schmus and .…”

Structural Underpinnings and Neotectonics of the Southern Illinois Basin: An Overview

“…The limits of the basin are arbitrarily defined as extending to the crests of the surrounding arches and domes (Kolata et al, 1992). The (Lidiak, 1996). The (Lidiak, 1996).…”

“…Published U-Pb zircon age measurements indicate that the province formed between 1.48 to 1.44 Ga Van Schmus and Bickford, 1981;Hoppe et aL, 1983;Thomas et al, 1984;Van Schmus etaL, 1987). Basalt was encountered at the top of crystalline basement in Lawrence County, Indiana, and Webster County, Kentucky (Lidiak, 1996). Basalt was encountered at the top of crystalline basement in Lawrence County, Indiana, and Webster County, Kentucky (Lidiak, 1996).…”

“…Precambrian basement rocks in the Illinois Basin, as in other parts of the eastern Midcontinent, consist primarily of mesozonal and epizonal granite plutons and subordinate rhyolite that are all assigned to the Eastern Granite-Rhyolite province (Bickford et al, 1986;Lidiak, 1996). Published U-Pb zircon age measurements indicate that the province formed between 1.48 to 1.44 Ga Van Schmus and Bickford, 1981;Hoppe et aL, 1983;Thomas et al, 1984;Van Schmus etaL, 1987).…”