Scientists say these “scars” influence how seismic waves travel through the continent

Sep 16, 2013 20:51 GMT  ·  By
Evidence suggests North America traveled over a hotspot millions of years ago, had its underbelly scorched by it
   Evidence suggests North America traveled over a hotspot millions of years ago, had its underbelly scorched by it

Recent investigations indicate that, millions of years ago, North America's underbelly was scorched by a hotspot that the tectonic plate chanced to travel across. What's more, it still has “scars” that prove the scorching was fairly severe.

Writing in yesterday's issue of the journal Nature Geoscience, scientists details how, by examining how seismic waves travel across the US' Midwest, they came to suspect that this patch of land has a so-called finger of heat that runs from central Missouri to Massachusetts beneath it.

This finger of heat is basically a band of deep continental crust rocks whose temperature is greater than that of their surroundings. It is likely that this band of hotter-than-average rocks is what slows down seismic waves passing through the area.

Researchers theorize that its increased temperature is due to residual heat that the rock forming it accumulated while journeying over the hotspot.

What they mean is that, just as a plate that is passed over a flame has part of its bottom burned, the North American tectonic plate's underbelly was at one point scarred by a plume of hot material originating deep in the Earth's mantle.

Such plumes are known to the scientific community as hotspots, Nature tells us.

The scarring occurred as the tectonic plate was traveling westwards during the Mesozoic Era. Thus, the hotspot first hit present-day central Missouri. This happened about 90 million years ago.

As North America continued to move, the hotspot carved a path towards eastern Kentucky (roughly 70 million years ago), and then worked its way to Massachusetts (60-50 million years ago).

Eventually, it moved offshore. By the looks of it, it now sits in the Atlantic Ocean.

The slowdown of seismic waves in this part of the US is not the only thing that hints at the presence of a warm trail left behind by a hotspot that burned the North American tectonic plate from beneath millions of years ago.

Thus, the fact that volcanic rocks known as kimberlites have been found in the state of Kentucky also indicates that this tectonic plate was at one point in its history exposed to a hotspot.

Researchers explain that, all things considered, the hotspot failed to cause volcanoes to form across the US Midwest due to the fact that, unlike thin oceanic crusts, this tectonic plate is fairly thick and therefore not very easy to breach.