T158 Beyond EarthScope in the Eastern U.S.—What We've Learned and What Needs Doing Next

Tuesday, 6 November 2018
8:00 AM - 12:00 PM
Room 238-239

MULTIDISCIPLINARY APPROACH TO CHARACTERIZE TECTONIC HISTORY OF THE MIDCONTINENT USA CRATONIC PLATFORM: THE OZARK PLATEAU - ILLINOIS BASIN BOUNDARY

Paper number: T158-11
Program: Technical Sessions
Time: 10:20 AM – 10:35 AM

Authors

Abstract

The Midcontinent USA cratonic platform was modified by several tectonic events, producing basins and domes and fault-and-fold zones. Data from EarthScope arrays and other sources covering the Ozark Plateau (Missouri) and Illinois Basin exemplifies how a multidisciplinary study can provide insight into the history of this tectonism. The Ozark Plateau, underlain by the structural Ozark Dome (OD), rises 0.7 km above the adjacent Illinois Basin (IB). Structural relief across this boundary, as defined by a DEM of the Great Unconformity, locally exceeds 7 km. Since the same suite of 1.47 Ga felsic extrusive rocks underlie the Great Unconformity of both provinces, the top of crystalline basement lay at the Earth's surface then. Subsequent rifting established a rectilinear array of steep fault zones cutting across basement. EarthScope MT data reveals a distinct NW-trending zone of low electrical resistance (the Missouri High-Conductivity Belt) across Missouri, suggesting some zones focused fluid flow in the past. Notably, this belt correlates with the Missouri Gravity Low, with magnetic anomalies, and with local fault traces. Thermal history modeling of zircon (U-Th)/He dates constrains protracted reheating during the Mesoproterozoic, indicating sedimentary burial in excess of 6 km (perhaps by Grenville foreland deposits), followed by Neoproterozoic cooling (i.e. exhumation) to form the Great Unconformity prior to Rodinia breakup. The OD and IB developed due to differential vertical motion that began in the Cambrian. Seismic data (including OIINK results) suggests that differential subsidence may be influenced by Moho-depth variations. Structure-contour maps, surface-geology maps, and seismic-reflection profiles emphasize that fault-and-fold zones reactivated multiple times, and that epeirogenic movement was localized by faulting. The seismically active Ste. Genevieve fault represents the surface manifestation of the OD-IB boundary. Apatite thermochronology suggests that Mesozoic exhumation removed post-Pennsylvanian cover prior to Pangaea breakup. The association of exhumation with supercontinent breakup suggests a link between mantle phenomena and uplift. Post-Pangaea river incision of OD bedrock and ongoing seismicity along the plateau’s borders suggest that uplift slowly continues.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322267

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