Most of the crater lies submerged on India's continental shelf, in the area known as Bombay High. The impact appears to have sheared or destroyed much of the 48 km-thick granite layer in the western coast of India.
Sankar Chatterjee of Texas Tech University and his team took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and natural gas. Some complex craters are among the most productive hydrocarbon sites on the planet.
“If we are right, this is the largest crater known on our planet,” Chatterjee said. “A bolide of this size, perhaps 40 km in diameter, creates its own tectonics.”
In contrast, the object that struck Mexico's Yucatan Peninsula, and is commonly thought to have killed the dinosaurs, was between eight and 10 km wide.
It's hard to imagine such a cataclysm. But if the team is right, the Shiva impact vaporised earth's crust at the point of collision, leaving nothing but ultra-hot mantle material to well up in its place.
The cataclysmic impact from outer space possibly triggered the nearby Deccan Traps volcanic eruptions that once covered much of western India. What's more, the impact broke the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa.
The geological evidence is dramatic. Shiva's outer rim forms a rough, faulted ring some 500 km in diameter, encircling the central peak, known as the Bombay High, which would be nearly five km higher than the ocean floor, said a Texas Tech release.
“Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly,” Chatterjee said. Asteroids are rich in iridium, and such anomalies are thought of as the fingerprint of an impact.
Chatterjee, who did his B.Sc and M.Sc in Geology from Kolkata's Jadavpur University in 1962 and 1964 and Ph.D from Calcutta University in 1970, will present his study at this month's annual meeting of the Geological Society of America in Portland, Oregon.
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