This is the Midwest’s biggest geologic mystery: What caused the giant 2,000-mile-long rift that starts in Lake Superior and runs south to Oklahoma and Alabama? Was the Midcontinent Rift part of a successful seafloor-spreading episode?
This is what propose geologists using new data from the North American Midcontinent Rift and observations of rifting occurring today between Africa and Arabia. According to the new theory, the Midcontinent Rift formed when rocks now in South America rifted away from North America, forming a new ocean. As a result, rocks from the two sides match like pieces of a jigsaw puzzle.
In other words, the ~1.1 Ga Midcontinent Rift (MCR), the 3000 km long largely buried feature causing the largest gravity and magnetic anomaly within the North American craton and traditionally considered a failed rift formed by isolated midplate volcanism and extension, formed as part of the rifting of Amazonia (Precambrian northeast South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established.
