Shocked quartz

Source: Wikipedia, the free encyclopedia.
Not to be confused with Fused quartz.
Photomicrograph
of shocked quartz

Shocked quartz is a form of

crystalline structure of quartz is deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are called planar deformation features
(PDFs), or shock lamellae.

Discovery

Shocked quartz was discovered following

Barringer Crater and Chicxulub crater.[1] The presence of shocked quartz supports that such craters were formed by impact, because a volcanic eruption would not generate the required pressure.[2]

Lightning is now known to contribute to the surface record of shocked quartz grains, complicating identification of

hypervelocity impact features.[3]

Formation

Photomicrograph of a shocked quartz grain (0.13 mm across) from the Chesapeake Bay impact crater, showing shock lamellae

Shocked quartz is usually associated in nature with two high-pressure

eclogite facies metamorphism (or nuclear explosion), but are also found in sediments prone to lightning strikes and in fulgurites.[4][3]

Occurrence

Shocked quartz is found worldwide, and occurs in the thin Cretaceous–Paleogene boundary layer, which occurs at the contact between Cretaceous and Paleogene rocks. This is further evidence (in addition to iridium enrichment) that the transition between the two geologic periods was caused by a large impact.[5]

Lightning also generates planar deformation features in quartz and is capable of propagating appropriate pressure/temperature gradients in rocks and sediments alike.[6] This very common mechanism may significantly contribute to the accumulation of shocked quartz in the geologic record. Mantle xenoliths and sediments derived from them may contain coesite or stishovite.[7]

Though shocked quartz is only recently recognized,

pseudotachylite, of Ries crater.[8][9]

See also

References

  1. doi:10.3133/ofr59108
    .
  2. Bibcode:1988LPICo.673...38D
    .
  3. ^
    S2CID 130973907
    . Retrieved 2018-08-07.
  4. S2CID 134575031
    .
  5. Bibcode:1988LPICo.673...17B
    .
  6. S2CID 130973907
    .
  7. doi:10.1016/j.jseaes.2008.10.012
    .
  8. doi:10.1029/JZ066i010p03371
    .
  9. ISBN 978-1-101-13322-4
    .

External links
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