Geology And Geophysics

The Formation of Kimberlites



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This is strictly hypothetical; Kimberlites have been emplaced during specific Earth ages like the late Cretaceous or during other specific ages associated with mass extinctions and/or impact craters. Many of these specific events seem to have coincided with massive impacts on the Earth by asteroids or comets such as the Chicxulub event on the Yucatan Peninsula at the end of the Cretaceous, 65 million years ago.

Geologists have long supported the theory that the Earth's crust is likened to an egg shell. Let us suppose that a major hit from a celestial body cracked the shell allowing some mantle material to escape through the cracks much like squeezing a grape or uncorking a warm bottle of champagne. This material would be under a very great pressure not only from the natural pressure generated by pressures in the Earth from depths of over 150 km, but also by the impact of the heavenly body itself. This would explain geologist's belief that kimberlites are emplaced at supersonic speeds. The upper mantle would act very much like grape pulp, and the entire sphere of the Earth would be deformed by the impact making it ring like a bell.

Large modern earthquakes around 9 or greater on the Richter scale cause this effect also, but the quake caused by this event would be far greater then anything that has been observed. This event would be greater then 14 on the Richter scale.

It has been posited that the Chicxulub asteroid was around ten kilometers in diameter meaning that the front of the asteroid was already in contact with the Earth's surface, and there were 10 kilometers of asteroid to go before the rear of the asteroid was flush with the Earth's surface. It is estimated that this body struck the Earth at a speed approaching 60 Km/sec. This collision was also accompanied by a tremendous amount of energy transferred to the Earth's body capable of cracking the crust, and forcing mantle material to the surface as kimberlites.

This event released an estimated 500 zettajoules (5.0 x 10x23) or approximately 100 teratons of TNT. The largest fusion bomb by contrast ever detonated was the Tsar Bomba (emperor bomb) by the Russians. This bomb had a yield of less then one twentieth of a gigaton. It is estimated that this collision at Chicxulub produced more then 2,000,000 times as much energy as the emperor bomb.

This is many; many times the energy of the atomic bomb we dropped on Hiroshima in fact it exceeded it by several million times. The Chicxulub event blew a crater into the Yucatan Peninsula 170 Km in diameter. It is reported that under the ice of Antarctica there is a crater that is 500 Km in diameter located in Wilkes Land. The existence of this crater has not been confirmed.

Was this the event that touched off the Permian extinctions?

Other large craters on the Earth's surface include the Vredefort Crater in South Africa at 300 Km in diameter. The Sudbury Basin in Ontario, Canada at 250 Km in diameter, and the Chicxulub Crater in Mexico at 170 Km in diameter.
We posit that this event sent a great shockwave through the Earth with one result being the Deccan Traps of southern India; one of the greatest deposits of volcanic material on Earth. The other consequence being the almost instant emplacement of kimberlite pipes on a world wide basis. This would explain many of the features associated with kimberlite pipes especially the evidence that the magma train falls back into the pipe at the end of the eruption. It also explains why this sort of eruption has not been observed by man. The Earth has not undergone a truly violent impact in millions of years. Further, the emplacement of kimberlite pipes has occurred at zones of crustal weakness that are characterized by either crossing deep seated faults, or areas that have undergone the folding and refolding of a fault line at depth.

This being said a profitable exercise might be to correlate the emplacement of kimberlite pipes with mass extinctions.

Any of the following events are capable of causing the emplacemnt of kimberlits.

References:

Chicxulub Crater, Wikipedia the Free Encyclopedia

Vredefort Crater, Sudbury Basin, Ibid

Wilkesland Crater, Ibid

Kimberlite, Ibid

Volcanic Pipe, Formation of Kimberlite, Ibid
Merguerian, Charles; and Ratcliffe, N. M., 1977, A reinterpretation of the Hodges Mafic Complex and its relation to deformation along Cameron's Line in West Torrington, Connecticut (abs.): Geological Society of America Abstract with Programs, v.9, p. 301-302.
Spray, J., Database of Earth Impacts, PASSC, University of New Brunswick, Fredericton, N.B.




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