North America’s “broken heart” is a 1.1 billion-year-old rift valley in the Midwestern United States, specifically in what is now the U.S. Midwest. The Midcontinent Rift is filled with solidified magma and lava, shaped like a horseshoe that stretches from Kansas to Lake Superior and south again to Michigan. Geologists estimate that the rift was around 1,900 miles long and created a basin as wide as the Red Sea.
The rifting process stalled about 100,000 years after it began due to unknown reasons, with scientists debating the cause of its failure. Theories include a mountain-building episode along North America’s Atlantic coast and the opening of a sea between Laurentia and Amazonia. However, one geologist describes it as a “spectacular failure,” highlighting the region’s fragile crust that may have weakened the surface.
The rift valley is now mostly buried beneath sediment, but parts are visible near Lake Superior, exposing huge blocks of basalt and other rift-related rocks. The area has attracted attention from resource exploration companies due to the potential for clean energy sources.
Source: https://www.livescience.com/planet-earth/geology/north-americas-broken-heart-the-billion-year-old-scar-from-when-the-continent-nearly-ripped-apart