Michael J Gagen
Strategic Optimization within Embedded Spaces
Asteroid Impacts and Mantle Plume Generation
Is it possible for asteroid impacts to immediately affect deep-Earth fluid motions, to initiate mantle plumes which, millions of years later, erupt through the crust as a hotspot creating a chain of volcanoes?
Take a look at the time sequence and the geometry of the asteroid strike that wiped out the dinosaurs. (See figure.) The asteroid struck the Yucatan Peninsular (left-most line) about (65 +/- 1) million years ago, while the Iceland 'hotspot' (middle line) erupted through the crust about (62 +/- 2) million years ago, and the Reunion 'hotspot' (right line) erupted to form the Deccan Traps in India about (66 +/- 2) million years ago. Is it possible that the impact energy passed into the Earth, was reflected and refracted from the denser core and generated the mantle plumes that lead to the two hotspots. (These are still currently active by the way.)
According to the The PALEOMAP Project and the ODSN Plate Tectonic Reconstruction Service, the position of the Chicxulub impact site at Yucatan 65 Myr ago was roughly where it is today. The Chicxulub impact site at Yucatan, Mexico is currently at N 21° 20' and W 89° 30' and occurred at 64.98 ± 0.05 million years ago.
This idea is partly incorrect and partly not testable, but establishing this makes for some interesting research.
The debate over the extinction of the dinosaurs about 65 million years ago has focussed on two possible causes. These two possibilities which might have so changed the Earths atmosphere as to kill off the dinosaurs are the massive volcanic eruptions creating the Deccan Traps in India, or alternatively, an asteroid impact at the Chicxulub impact structure (diameter 180km) on the Yucatan peninsular. For surveys, see references [1,2]. Climatic effects of the Chicxulub impact are modeled in .
The coincidence in timing of the Deccan Traps eruptions at (66 +/- 2) Myr and the asteroid impact (65 +/- 1) Myr raised the obvious question of whether these two events are linked. This was answered in the negative by investigations that placed the iridium impact signature within the Deccan Trap sediments . This finding also made it unlikely that these large lava outflows were the result of an Indian asteroid impact which triggered a basalt melt and triggers volcanism .
A number of letter writers have sought to link the impact and the Deccan Traps by suggesting that these events were antipodal [6-8]. This would mean that the waves transporting the impact energy through the Earth are focussed and increased in amplitude in the crust of the impact antipodal point. The deposition of energy would (hopefully) bring out a basalt melt and trigger volcanism.
For interest, extinctions have been proposed to occur with a periodicity of around 26.6Myr which correlates well with the period of passage of the Earth through the Galactic plane (approximately 30 Myr). See .
Asteroid Impacts and Mantle Plumes
A novel idea not previously investigated considers whether impact energy can travel through the Earth to be refracted to the antipodes and reflected from the density changes within the mantle and the core. Rarefaction and reflection of earthquake waves is well known as shown below.
Is it possible that the interaction of the energy wave with the mantle and core could deposit sufficient energy to initiate a mantle plume which slowly travels upwards to the crust to create a vulcanic hotspot. This idea might link the asteroid impact (65 +/- 1) Myr to possibly increased outpourings in the already active Deccan Traps (66 +/- 2) Myr and the initiation of the Iceland hotspot which commenced around (62 +/- 2) Myr.
Recent investigations have suggested that the Chicxulub impact occurred at an 20-30 degrees to the horizontal and in a generally North-West direction [10,11]. This argues against the idea presented here.
Final decisions about these ideas wait for considerable refinements in whole-Earth modeling capabilities. Current models adequately show the transmission of energy through the Earth, but lack the detail to show reflected waves from mantle and core density gradients. See for instance .
 W. Alvarez, F. Asaro, "An extraterrestrial impact", Scientific American, 44-42, October 1990
 V. E. Courtillot, "A volcanic eruption", Scientific American, 53-60, October 1990
 K. O. Pope, K. H. Baines, A. C. Ocampo, B. A. Ivanov, "Impact winter and the Cretaceous/Tertiary extinctions: Results of a Chicxulub asteroid impact model", Earth and Planetary Science Letters, 128, 719-725 (1994)
 N. Bhandari, P. N. Shukla, Z. G. Ghevariya, S. M. Sundaram, "Impact did not trigger Deccan volcanism: Evidence from Anjar K/T boundary intertrappean sediments", Geophysical Research Letters, 22(4), 433-436 (1995)
 D. Alt, J. M. Sears, D. Hyndman, "Terrestial Maria: The origins of large basalt plateaus hotspot tracks and spreading ridges", The Journal of Geology, 96(6), 647-662, 1998
 R. N. H. Whitehouse, New Scientist, 52, 14 September 1996
 T. E. Groves, New Scientist, 52, 14 September 1996
 D. Turnbull, New Scientist, 57, 19 October 1996
 M. R. Rampino, K. Caldeira, "Major episodes of geologic change: correlations, time structure and possible causes", Earth and Planetary Science Letters, 114, 215-227 (1993)
 P. H. Schultz, S. DHondt, "Cretaceous-Tertiary (Chicxulub) impact angle and its consequences", Geology, 24(11), 963-967 (1996)
 J. Hecht, "Fresh angle on dead dinosaurs", New Scientist, 14, 12 October 1996
 K. Jach, J. Leliwa-Kopystynski, M. Mroczkowaki, R. Swierczynski, P. Wolanski, "Free particle modelling of hypervelocity asteroid collisions with the Earth", Planetary and Space Science, 42 (12), 1123-1137 (1994)
Sources of Illustrations
|Michael J Gagen|
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