Did The Chicxulub Impact Trigger the Deccan Traps?
The extinction of those most charismatic of ancient animals, the dinosaurs, 65 million years ago is still something of a mystery. There is overwhelming evidence of an asteroid crashing into the Gulf of Mexico at the right time to have triggered the extinction, but the picture is complicated by the near-simultaneous eruption of a massive amount of magma in India. Known as the Deccan Traps this 200,000km2 expanse of lava is known as a flood basalt eruption, and it is not the only one known from prehistory. In fact another large, famous flood basalt eruption formed the Siberian Traps and they themselves are associated with the largest extinction to ever challenge life on Earth. Very recently the Deccan Traps were more precisely dated and although they began erupting long before the extinction the majority (70%) of the basalt, known as the Wai subgroup, erupted comparatively quickly within 100,000 years of the end-Cretaceous extinction. This led to the suggestion that the Deccan Traps, rather then the asteroid, may have wiped out the dinosaurs (see previous article).
However, the truth may be more complicated still. A new paper from the University of California, Berkeley has investigated this possible connection. They started by the assumption that such a synchronicity between the impact and the eruptions was unlikely to be a coincidence and set out to find a plausible connection. The idea that an impact could trigger an eruption is not entirely new but it is important to distinguish this new work from the previous theory which involved a process named ‘antipodal focusing’. This idea postulated that an asteroid impact of sufficient magnitude would trigger eruptions on the Earth’s surface directly opposite the impact. However, such a suggestion was quickly discounted when the actual Chicxulub impact crater was discovered and the Deccan Traps were found to be 5000km off the antipode.
Instead the new theory accounts for the fact that the Deccan Traps had been erupting at a low level long before the impact. Some earthquakes have been shown to be able to trigger nearby volcanoes and simulations suggest that the asteroid impact may very well have triggered high magnitude quakes across the world. The effect of these tremors on the Deccan Traps is theorised to have mobilize a huge amount of underground magma, bringing it to the surface in a new, massive eruption which created the Wai subgroup. This would also account for the difference in lava chemistry between that erupted before and after the asteroid impact. Although the researchers were keen to stress that this still doesn’t necessarily explain how such an event could have caused the extinction itself cataclysmic climate change would seem to be a plausible mechanism. More work is undoubtedly needed but it now seems that rather then suffering from one of two competing causes the dinosaurs instead fell victim to a geological tag-team. This new discovery also opens the way for further research on other ancient extinctions and the flood basalts associated with them.
Reference: Richards, M. A., et al. 2015. Triggering of the largest Deccan eruptions by the Chicxulub impact. Geological Society of America.
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