Researchers have identified a section of ancient oceanic crust beneath the Midwest that is pulling present-day North American crust into the mantle. This process has created large geological “drips” extending about 640 kilometres below the surface.
The affected region stretches from Michigan to Nebraska and Alabama. The geological structure resembles a funnel, where rock from different parts of North America is being drawn horizontally before sinking downward.
The study suggests that the downward movement is caused by a remnant of the Farallon plate, an ancient oceanic plate that once subducted beneath North America. This slab detached approximately 20 million years ago and is now deep within the mantle.
The process, known as cratonic thinning, is altering stable regions of continental crust that have remained largely unchanged for billions of years. This is the first time scientists have observed this phenomenon as it occurs.
Using high-resolution seismic imaging, researchers mapped the subsurface of North America. The technique, known as full-waveform inversion, allowed them to analyse seismic waves and detect the large-scale geological movement.
Simulations showed that the presence of the Farallon slab directly influences the formation of the geological drips. When the slab was removed from the model, the dripping effect disappeared, confirming its role in the process.
While this geological activity is significant, scientists do not expect it to cause noticeable surface changes in the near future. Over time, the process may slow down as the Farallon slab continues sinking deeper into the mantle.