Geological Oddity: Scientists Discover Hotspot Track Cross-Cutting the New Madrid Rift System

Geological Oddity: Scientists Discover Hotspot Track Cross-Cutting the New Madrid Rift System

Could this hotspot track cross-cutting the New Madrid Rift System explain the reactivation of the New Madrid rift system and seismicity of the eastern United States? Some geologists think they might have found the buried track of just such a hotspot from Missouri to Virginia.

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Image: The rectangular boxes show the locations of the seismic anomalies detected by USArray. The blue line shows the track of the hot spot. Black triangles are where diamond-bearing rocks from deep in the mantle have been found. Black and red lines are the boundary of the Mississippi Embayment and the New Madrid rift complex, respectively.  The inset globe shows where the hotspot is today and the ball shows the epicenter of the 2011 Virginia earthquake.

In an article in the magazine Nature Geoscience, Chinese and American scientists describe what they think to be the track of a hotspot hidden in the very old, thick crust of Eastern United States, based on seismic data from the 2011 Virginia 5.6-magnitude earthquake.

As shown in the figure, the seismic data has revealed an unexpected scar in the lower part of the crust extending from eastwards from Missouri to Virginia. This seismic anomaly cuts through the New Madrid rift system, which is responsible for some of the most powerful earthquakes in North American history. It also crosses a 75-million-year-old diamond-bearing formation in Kentucky. Despite all this, there is no sign of the hotspot track on the surface.

Here the abstract of this scientific research:

Hotspot tracks are thought to be the surface expressions of tectonic plates moving over upwelling mantle plumes, and are characterized by volcanic activity that is age progressive. At present, most hotspot tracks are observed on oceanic or thin continental lithosphere. For old, thick continental lithosphere, such as the eastern United States, hotspot tracks are mainly inferred from sporadic diamondiferous kimberlites putatively sourced from the deep mantle. Here we use seismic waveforms initiated by the 2011 Mw 5.6 Virginia earthquake, recorded by the seismic observation network USArray, to analyse the structure of the continental lithosphere in the eastern United States. We identify an unexpected linear seismic anomaly in the lower lithosphere that has both a reduced P-wave velocity and high attenuation, and which we interpret as a hotspot track. The anomaly extends eastwards, from Missouri to Virginia, cross-cutting the New Madrid rift system, and then bends northwards. It has no clear relationship with the surface geology, but crosses a 75-million-year-old kimberlite in Kentucky. We use geodynamical modelling to show that an upwelling thermal mantle plume that interacts with the base of continental lithosphere can produce the observed seismic anomaly. We suggest that the hotspot track could be responsible for late Mesozoic reactivation of the New Madrid rift system and seismicity of the eastern United States.

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