Thin section from The Deccan Traps, India

by Joe Zink March. 31, 2018 595 views

Roughly 66 million years ago, a huge asteroid slammed into the earth somewhere near present-day Yucatan, in Mexico. Within the same geological age, a hot plume of magma broke through the earth’s crust in what is now central India, on the opposite side of the earth from the impact.

It’s thought that the eruptions actually began before the impact, but during that time strange things began to happen to the magma body on the other side of the planet, as evidenced by the rock that remains visible to this day.

Scientist have determined that there was a pulse of unusually rapid tectonic plate motion during this time period. The pace of eruptions increased, and the onset of the rapid movement of the Indian plate coincides with a large slowing of the counter clockwise motion of the African plate. There is evidence that suggests the flow of lava may have become more permeable after the impact, erupting in greater volume.

Basalt lava continued to flow in India for millions of years, in a place called the Deccan Plateau. Known today as The Deccan Traps, this part of India is one of the largest volcanic features on the earth. Flood basalt more than 2,000 meters thick (6,600 ft.) covers much of the Plateau. The basalt flows currently cover an area of roughly 200,000 square miles (larger than the US states of Washington and Oregon combined), though estimates of the original flow are much larger…up to 600,000 square miles (1.5 million square km) may have been covered during the peak of the eruptions. It is thought that there were a mixture of very large events and much smaller events, happening at intervals that allowed some of the layers to cool before a new layer was deposited.

For years, scientists have said that the dust and dirt kicked into the atmosphere by the impact event blocked the sun’s rays , causing the earth to cool. According to that theory, the cooling of the earth led to the mass extinction of the dinosaurs. But scientists are looking more closely at the volcanism in the Deccan Traps, and are considering the out poring of lava and noxious gases and increased heat in the atmosphere from the volcanic eruptions may have combined with the effects of the asteroid impact to cause a “one-two” punch that ultimately led to the extinction of the dinosaurs.

This thin section is a sample of rock from the Deccan Traps near the Ghat mountains in India. Typical for hot thin magma layers, it contains a large volume of very small particles that cooled too quickly to grow into large crystals. However, it does contain a few very nice crystals that had an adequate amount of time to form.

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Sigrid Strohschneider-Laue 1 year, 5 months ago

Very interesting - my husband, looking over my shoulder, just added some comments too!

1 year, 5 months ago Edited
Joe Zink Replied to Sigrid Strohschneider-Laue 1 year, 5 months ago

I'm almost scared to know what kind of comments Roland made ...grinning

1 year, 5 months ago Edited
Antonio Gil 1 year, 5 months ago

Thank you so much for your geological lessons my friend. Much appreciated information and very well achieved pictures

1 year, 5 months ago Edited
Joe Zink Replied to Antonio Gil 1 year, 5 months ago

Thanks, Antonio !
It will be spring here in another month or so, and I can put the microscope away for awhile then.
We'll have to see if I can remember how to take a picture of something larger than an ant's ass. grinning

1 year, 5 months ago Edited
Antonio Gil Replied to Joe Zink 1 year, 5 months ago

Hahahahaha. Great sense of humour Joe

1 year, 5 months ago Edited