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Did K-T extinction event meteor puncture a hole in crust at Chicxulub?

  1. Jul 20, 2012 #1
    Did the meteor or comet that struck Earth at the end of the Cretaceous punch a whole in the crust down to the mantle? If so, why isn't that part of the crust weak and showing signs of volcanism? Even if the crust wasn't punctured down to the mantle, wouldn't it still be a weak spot and show volcanic signs -- sort of like "hot spots".
  2. jcsd
  3. Jul 21, 2012 #2
    Schutte et many al 2010 is the report on probably the most comprehensive research. The verdict is that it was the impact:

    There is little use to speculate about volcanism associated the impact side, there may be a relation between impacts and volcanism and it may have been there or not, but it seems that somebody is yet to discover evidence of associated volcanism locally.

    Notice that the large Deccan volcanic events in India, also associated with the extinction, started million years before the impact.
  4. Jul 21, 2012 #3
    Thanks for the response.
  5. Jul 22, 2012 #4
    Whisper Gallery effect.
    I don't claim to know whether the shock wave from "antipodes" theory is correct or not. Some scientists claim that the Deccan Trappes started a million years before the KT impact. However, I am not sure this "fact" will prove robust. However, I can explain the reasoning that goes into the antipodes effect, right or wrong.
    The "antipodes theory" claims that the basaltic flow of the Deccan Trappes started on the side opposite the impact because of the whisper gallery effect. The shock waves spread out from the point of impact. However, the shock waves were refocused on the far end of the earth by the whispering gallery process. The earth acted like a reflective lens. The basaltic flow was caused by cavitation on the “free” end of the earth, somewhat like the free end of a plate after impact by a projectile.

    Here is a link to an article stating the hypothesis.
    The shock waves, rippling through the Earth, would take about 80 minutes to travel to the antipode, creating a pipeline of destruction from the depths of the Earth to the surface. It is theorized that a huge eruption, in what is now India, created the great lava fields known as the Deccan Traps about 65 million years ago. However, the antipode to the Deccan Traps is not in the vicinity of the great Chicxulub crater, but rather it is located in what is now the eastern Pacific Ocean where the seabed bears evidence of a major impact. Perhaps, as some experts suggest, two or more meteors struck the Earth simultaneously.

    The whispering gallery wave are described here.
    “Whispering-gallery waves, or whispering-gallery modes, are a type of wave that can travel around a concave surface. Originally discovered for sound waves in the whispering gallery of St Paul’s Cathedral, they can exist for light and for other waves, with important applications in nondestructive testing, lasing, cooling and sensing, as well as in astronomy.”

    Notice that in ordinary spallation, without a whispering gallery, the major damage occurs opposite the impact site. The multiple fragments are released on the “free end” of the plate. The impacting projectile blocks fragments from flying off at the point of impact. Internal cavitation due to stresses occurs on the free end, not the impacted end.

    Here is a link to plate spallation.
    “Spallation can occur when a tensile stress wave propagates through a material and can be observed in flat plate impact tests. It is caused by an internal cavitation due to stresses, which are generated by the interaction of stress waves, exceeding the local tensile strength of materials. A fragment or multiple fragments will be created on the free end of the plate. This fragment known as "spall" acts as a secondary projectile with velocities that can be as high as one third of the stress wave speed on the material. This type of failure is typically an effect of high explosive squash head (HESH) charges.”
  6. Jul 22, 2012 #5
    Darwin123, Thanks for the response. I have read some about an antipodal point to a collision point -- but not much.
  7. Jul 23, 2012 #6
    In relation to the robustness of the 40Ar datings of the deccan traps, how robust would the antipode position be for Deccan Chicxulub line up? there are a lot of reported remagnetizations (see refs), which could potentially challenge the currect paleo pole positions and the precieze continental drift.

    Font et al 2011; Paleomagnetism and rock magnetism of the Neoproterozoic Itajaí Basin of the Rio de la Plata craton (Brazil): Cambrian to Cretaceous widespread remagnetizations of South America, Gondwana Research Volume 20, Issue 4, November 2011, Pages 782-797

    Liu, Chengying, Kunpeng et al, 2011 Nature of remagnetization of Lower Triassic red beds in southwestern China, Geophysical Journal International Volume 187, Issue 3, pages 1237–1249, December 2011

    Rowan, C. J., and A. P. Roberts (2008), Widespread remagnetizations and a new view of Neogene tectonic rotations within the Australia-Pacific plate boundary zone, New Zealand, J. Geophys. Res., 113, B03103, doi:10.1029/2006JB004594

    T. H. Torsvik et al 2005, Remagnetization of Mesozoic limestones from the Jaisalmer basin,
    NW India Geophys. J. Int. (2005) 161, 57–64 doi: 10.1111/j.1365-246X.2005.02503.x
  8. Jul 23, 2012 #7
    Seismologists have looked at this antipodal focussing mechanism recently. Lateral heterogeneous elliptic Earth's with realistic source mechanisms dampen the effect four fold relative to spherically symmetric models with points source. However, the effect remains significant.

    Meschede et al. Antipodal focusing of seismic waves due to large meteorite impacts on Earth. Geophys J Int (2011) vol. 187 (1) pp. 529-537
  9. Jul 23, 2012 #8
    I am not championing the antipode theory. I am just presenting it for discussion.
  10. Jul 24, 2012 #9
    That's exactly what I do too. It's just interesting to see when the jury comes out.
  11. Aug 10, 2012 #10
    There is no evidence for active volcanism at Chicxulub. The bolide struck a carbonate shelf creating a transient crater ~100km in diameter and ~35km deep, with a final diameter of ~185km x ~12km deep. The melt sheet is ~1.5km - ~3km thick; and as with all large impacts, ~half the volume of the melt sheet is impactor.

    India was not antipodal to Yucatan 65Mya. http://www.geog.nau.edu/courses/alew/gsp220/text/chapters/ch2.html

    There is, however, another proposed crater east and south of Mumbai. It is two and a half times the diameter as Chicxulub and also dates to 65Mya. https://gsa.confex.com/gsa/2003AM/finalprogram/abstract_58126.htm. This is only a proposed crater. If the known topology is actually a crater, it is astoundingly large. So large it would send the geophysicists back to the drawing board to redetermine just how much dust and ash is needed to create an extinction event.

    You can study it's gravity anomaly here ( http://www.virtualocean.org/) and compare it to Vredfort, Chicxulub, Popigai, Manicouagan and Ust-Kara, all of which have prominent free air gravity anomalies, and are quite noticeable once you get an idea of what to look for. Remember, the appearance of the gravity anomaly doesn't necessarily match the crater form itself.

    A note about the antipodal theory. There are a number of large, D>300km, impacts extant on Mars, the Moon and Mercury. There is only one case where possible antipodal activity is present. The chaotic terrain opposite Caloris basin on Mercury. The jury is still out.

    A note on extinction events. Chicxulub is associated with the end Cretaceous extinction. The final crater has a ~185km diameter. However, there are two large craters (85km and 100km) at 35Mya; the dating of which overlap closely enough that they may have formed simultaneously, and no more than 600Ky apart in any case. No extinction event is associated with these impacts. Only local environmental disruption has been found. I find this lack of global disruption, interesting.
  12. Aug 10, 2012 #11


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  13. Aug 10, 2012 #12
    Thank you Shootist for a very informative reply.
  14. Aug 10, 2012 #13
    Not all bolide impacts are alike. There are more factors that contribute to extinction than the mere size of the bolide.
    For example, the KT asteroid may have landed in a large bed of gypsum, resulting in an increase of the frequency of acid rain. Later impacts, such as 35 MYA, may not have landed in a bed of gypsum.
    Here is a link to an article on the KT extinction. The article is quoted as saying that landing in a bed of gypsum
    “The asteroid landed in a bed of gypsum (calcium sulfate), which would have produced a vast sulfur dioxide aerosol. This would have further reduced the sunlight reaching the Earth's surface and then precipitated as acid rain, killing vegetation, plankton and organisms which build shells from calcium carbonate (coccolithophores and molluscs). In February 2008, a team of researchers used seismic images of the crater to determine that the impactor landed in deeper water than was previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere, which could have made the impact deadlier by altering climate and by generating acid rain.”

    The angle of the impact may have affected which areas on earth were affected most. It is possible that many species of animals and plants in North America may have gone extinct at the KT because the debris was projected in the direction of North America. Maybe the impacts 35 MYA were more straight on, or maybe the debris was projected between continents.
    “These asymmetric signatures suggest a trajectory for the Chicxulub bolide from the southeast to the northwest at a 20°–30° angle from the horizontal. As a result, biotic extinctions may have been most severe and catastrophic in the Northern Hemisphere.”
  15. Aug 10, 2012 #14
    Antipodal to what, Imbrium and Procellarum? I suppose. Though I don't see the relationship between the existence of farside magnetic fields and impacts on the nearside. High energy events tend to demagnetize rock, plus it has been several eons since Luna had an active magnetic field; probably lost within 500 My of formation.

    Another consideration, except for the mares, the lunar surface is over saturated by bombardment. IOW, none of the surface prior to 3.9-3.8Gya remains. As the large, basin forming (D>900Km) events on lunar near side date to ~4.1Gya, and before (except for the late forming Orientale), any antipodal disruption should be covered by kilometers of debris. In fact, the crustal thickness of lunar farside averages 12km thicker than nearside. The lunar crust isn't so much a solid lithosphere, such as we think of Earth, as a rubble pile (broken up all the way down to 60km or so).

    Steve, do you have the document/website this png came from? I'd like to review it. The locations appear to be the same as several proposed buried basins that have only come to light as recent LRO observations have been studied (laser altimeter data combined with gravity data).
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