High-precision timeline helps clarify an ancient magma surge in the North Cascades
Where oceanic crust subducts beneath continental crust, belts of volcanoes known as continental arcs can form. Located around the world, these arcs may undergo episodic magma flare-ups—dramatic surges in the flow of magma into the continental crust at rates up to 20 times higher than normal. However, what triggers these extreme surges, which last tens of millions of years, can be unclear.
A powerful surge of magma in the ancient North Cascades region occurred between 79 million and 60 million years ago. This event, part of a larger volcanic arc known to have been active from roughly 150 million to 50 million years ago, involved massive quantities of magma cooling and crystallizing deep within the Earth's crust. Today, the area is experiencing a different kind of volcanic activity, with Mount Rainier and Mount Baker among its more recent notable volcanoes. However, remnants of the ancient magma are present in the region's geological structure.
Scientists have long debated whether the thickening of the continental crust during this period was a cause, a result, or a separate phenomenon. By meticulously examining rock samples from the region and employing advanced dating techniques, researchers were able to construct a precise timeline of the event. Utilizing zircon dating and geochemical analysis, they determined that the crustal thickening did not begin until after the magma flare-up had commenced.
The study suggests that the flare-up was more likely the consequence of crustal thickening, rather than its cause. This correlation supports the idea that crustal thickening may be a consequence of the magmatic activity, rather than the trigger for it.
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