A PRELIMINARY GEOPHYSICAL STUDY OF THE MIDCONTINENT RIFT SYSTEM IN IOWA

The Proterozoic Midcontinent Rift System (MCRS) is one of the most prominent tectonic features in the United States. As evidenced by prominent positive gravity and magnetic anomalies that trend from northwest Michigan to northern Oklahoma. The 2000 km long MCRS has two major arms meeting in the Lake Superior region. One extends southwestward at least as far as northern Oklahoma, and the other extends southeastward at least through Ohio. Because the rift is hidden beneath Phanerozoic sedimentary rocks except where it is exposed in the Lake Superior region, its location and geological characteristics are primarily inferred from the gravity and magnetic anomalies, extrapolations from the outcrop area, seismic reflection profiles, and a few basement drill holes. The MCRS is notable because along its 2000 km-length formed during a continental breakup event 1.1 Ga, contains an enormous volume of igneous rocks that are mostly flood basalts. Many questions remain regarding not only the main source caused the MCR, but also the origin of the magma neither from a microplate interaction with another one at spreading ridge at West & transform fault at East nor from the mantle plumes. The Iowa portion of the MCRS is relatively unstudied geophysically and we will analyze gravity, magnetic and Earthscope long period magnetotelluric (MT) data in order to determine the crustal structure of the MCRS. This will be accomplished through the construction of residual and regional gravity and magnetic anomaly maps, 2D gravity and magnetic models, and 2D and 3D MT models. These models will aid in determining the crustal structure and if there is any remnant rift anomalies in the upper mantle.