ZAP // Vannessalai / Wikipedia
A new study reviews the history of the fragmentation of Pangea, the supercontinent whose separation paved the way for the configuration of the continents we know today.
The Triassic period ended when a gigantic amount of molten igneous rock, known as Central Atlantic Magmatic Province (CAMP), erupted from the Earth’s mantle and infiltrated the crust beneath what is today the eastern foothills of the Appalachians.
Millions of years later, the supercontinente Pangeia began to open up, with the east coast of what is now North America separating from West Africa, giving rise to the Atlantic Ocean.
In geological terms, these two events occurred sufficiently close in time so that many researchers consider that the appearance of this magmatic province triggered the beginning of the fragmentation of Pangea.
But new research, led by the University of Texas Institute for Geophysics (UTIG), concludes that CAMP’s role in the breakup of the supercontinent was not as decisive as previously thought.
Scientists suggest that another magmatic riseresponsible for the formation of the tectonic structure known as the East Coast Magnetic Anomaly, could have been the real engine of the great fragmentation of Pangea.
This event occurred million years after CAMPalong the east coast of the United States.
“Continental separation caused a second pulse of magmatism off the eastern United States, along the East Coast Magnetic Anomaly, 15 million years after CAMP,” he said. Harm Van Avendonkresearch professor at the Jackson School of Geosciences and UTIG and lead author of the article, at UTIG.
“It is a significant delay, which casts doubt on the idea that CAMP triggered the opening of the Atlantic Ocean.”
Investigators found solid evidence that this subsequent pulse of magmatism will iboosted the opening of the supercontinent during seismic cartography work on the east coast of the United States.
The team was looking to obtain a more complete picture of the Earth’s crust in the North American Atlantic Coastal Plain, in particular between the eastern foothills of the Appalachians and the deep seafloor of the western mid-Atlantic region.
This section covers the structures of the Earth’s crust and mantle resulting from rifting and continental separation that occurred around the time the CAMP emerged, including the East Coast Magnetic Anomaly.
The team carried out a series of surveys on land and at sea to measure seismic velocity — the speed at which sound travels through rocks of the crust and upper mantle—along these areas of the East Coast.
The researchers concluded that magmatism associated with the opening of the Atlantic Ocean did not originate from CAMP; occurred offshore, along the East Coast Magnetic Anomaly.
Survey results showed that the crust beneath the foothills was about 35 kilometers thick and becoming narrower as it approached the anomaly, with only the lower few kilometers of crust showing seismic velocities compatible with those of magmatic rock.
For CAMP to have a significant influence on crust separation, there would have to be a much thicker layer of material with seismic wave velocities similar to those of magmatic rocks.
In contrast, in the anomaly zone there are signs of narrow rifts that were filled by magma after they were formed. This is a typical structure of the crust resulting from continental separation.
“The eastern margin of North America has long been considered a paradigmatic example of magma-rich rifting associated with the CAMP,” he said. Donna Shillingtonco-author of the article and professor at the School of Earth and Sustainability at Northern Arizona University.
“But these conclusions demonstrate that the volume and distribution of magmatism on this margin, including that of the CAMP, are very variable, and that the link between the CAMP and continental separation is not as simple and clear as supposed”, concludes the researcher.
