The Great Subterranean Sink: North America Is Dripping Into the Deep Earth

The phenomenon of "dripping" beneath North America, resulting from the ancient Farallon plate's influence, represents a significant advancement in our understanding of geological processes. Recent studies reveal that this subducted oceanic crust is exerting a downward pull on the continental lithosphere, leading to a process known as "cratonic thinning" . This research highlights the gradual yet impactful changes occurring deep within the Earth, affecting regions extending from Michigan to Alabama. The identification of large drip-like formations descending approximately 640 kilometers into the mantle underscores the dynamic nature of what was once considered stable continental crust .

Cratons are very old rocks that are part of Earth’s continents. They’re known for their stability and ability to persist for billions of years. But sometimes cratons undergo changes that can affect their stability or that remove entire rock layers.

For example, the North China Craton lost its deepest root layer millions of years ago.

What makes the discovery of cratonic dripping special, said the researchers, is that it’s happening right now. This allows scientists to observe the cratonic thinning process as it occurs.

The dripping is concentrated over the Midwest of the United States. There’s no need to worry about the continent hollowing out or the dripping changing the landscape anytime soon, the researchers assure. The mantle processes driving the dripping can influence how tectonic plates evolve over time – but they’re very slow going.  What’s more, the dripping is expected to eventually stop as the remnants of the tectonic plate sinks deeper into the mantle and its influence over the craton fades.

Using over 300 contextual parameters, they assiduously described individual vocalizations in the context of external events (like the presence of other bonobos), and the activities of the callers—e.g., eating, resting, playing. Following a call, they coded activities that occurred over the next two minutes. In this way, they determined that if a particular call preceded the bononbo beginning to travel, the call meant "I will travel." The result was what they describe as a complete dictionary of bonobo calls.

In the second step, they sought to learn whether combinations of calls were compositional—that is, whether the combinations modulated the greater meaning. Using methods derived from linguistics, they ultimately identified four call combinations whose meanings were derived from their single parts; every call type appeared in at least one of these combinations. This suggests that bonobo communication has compositionality.

To test their results, the researchers simulated the impact of the Farallon slab on the craton above using a computer model. A dripping area formed when the slab was present, but it disappeared when the slab was absent, confirming that — theoretically, at least — a sunken slab can drag rocks across a large area down into Earth's interior.

Dripping beneath the Midwest won't lead to changes at the surface anytime soon, the researchers said, adding that it may even stop as the Farallon slab sinks deeper into the lower mantle and its influence over the craton wanes.

The finding emerged from a broader project led by Hua, now a professor at the University of Science and Technology of China. Using a full-waveform seismic tomographic model built with data from the EarthScope project, developed by co-author Stephen Grand and his team, the researchers gained new insights into the crust and mantle beneath North America.

Read more

Sarah H

Also on site :

• South and Midwest floods worsen after heavy rains, almost 20 dead
• Minecraft Movie exceeds expectations, debuting with $157 million
• Falcon 9 to Carry 27 Starlink Satellites Skyward from Vandenberg