Tectonic Evolution of an Intracratonic Plateau: The Ups and Downs of the Ozark Dome, Midcontinent United States
Abstract
Though intracratonic platforms have been affected both by epeirogenic movements (producing regional-scale basins and domes) and by local faulting, they typically have low relief. The Ozark Plateau (OP) of Missouri, a region underlain by the structural Ozark Dome (OD), is an exception for it rises to elevations of up to 0.7 km above the surface of the adjacent Illinois Basin (IB). Structural and geomorphic analysis, and low-temperature thermochronology, provide insight into vertical movements of the OD relative to the IB. The basement top of both the IB and OP exposes 1.47 Ga extrusive rhyolite. Therefore, basement of both the IB and OD sat at the Earth's surface then. Rifting after emplacement established a rectilinear array of steep faults, which delineated what would become the OD, and set the stage for IB subsidence. Zircon (U-Th)/He thermochronology indicates that exhumation of the Midcontinent to form the Great Unconformity (GU) happened from 0.85 to 0.68 Ga. To reset the zircon system, the region must have been buried >4 km prior to 0.85 Ga, perhaps by Grenville foreland deposits. Deposition began on the GU at 0.5 Ga, burying paleotopography of the OD and IB. Differential vertical motion between these regions initiated in the Paleozoic. Strata thin towards the apex of the dome, emphasizing that the OD remained high during IB subsidence. Eventually, as much as 7.5 km of structural relief accumulated across the boundary between the OD and IB. Some of the movement was accommodated by fault slip that was coeval with Appalachian orogenies, emphasizing that orogenic stress penetrated into the continental interior. Faulting contributed to tilting the OD crustal block. Apatite (U-Th)/He and fission-track thermochronology suggests that Mesozoic exhumation removed post-Pennsylvanian cover. Both Proterozoic and Mesozoic exhumation events took place just before supercontinent breakup, suggesting a link between mantle phenomena and intracratonic elevation. Contemporary river incision of OP bedrock and ongoing seismicity along the OP's borders suggest that OP uplift continues, though a lack of knickpoints suggests the movement is very slow. The persistence of the OP through geologic time implies that Precambrian modification of continental-interior lithosphere continues to influence its geodynamic response today.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.T54A..07D
- Keywords:
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- 8110 Continental tectonics: general;
- TECTONOPHYSICS;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS