Presentation by Zoe Molitor.
Extreme Moho Relief Beneath the State of Ohio
The typical thickness of continental crust, away from plate boundaries and in the absence of significant topography, should be ~30-40 km. However, many examples of anomalously thick crust (>40-50 km), stable over 100s to 1000s of Myrs, exist. In this talk, I present new estimates of crustal thickness based on seismic data from the state of Ohio within the Midwest region of the United States. This region is deep within the interior of the North American plate and is characterized by extremely low topographic relief; however, crustal thickness is ~60 km beneath the central part of the state. Anomalously thick crust, together with narrow, positive gravity anomalies, suggest that the lower crust beneath central Ohio is characterized by a mafic crustal root. Mafic material was intruded and underplated beneath the North American lithosphere during Mid-Continent rifting at ~1109 Ma. Following rifting, the region experienced significant contraction and shortening during the collisional Grenville orogeny. I propose that the combination of neutrally buoyant mafic material in the lower crust and short wavelength Moho relief is necessary for the long-term stability of thick crust beneath Ohio. Thus, the anomalously high crustal thickness is likely a product of Ohio’s unique Precambrian history and has been stable for ~1000 Myrs. This model reconciles both seismic and gravity models of the crustal structure and geologic history beneath Ohio, suggesting that part of the Mid-Continent Rift was deformed and imbricated within the Grenville Front in the Proterozoic eon.
