Maniitsoq structure

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Maniitsoq structure
Maniitsoq structure is located in Greenland
Maniitsoq structure
Impact crater/structure
ConfidencePotential (2)
Diameter100 km (62 mi)
AgeMesoarchean
~3 Ga
ExposedYes
Location
Coordinates65°15′N 51°50′W / 65.250°N 51.833°W / 65.250; -51.833 (Maniitsoq)
CountryGreenland
MunicipalityManiitsoq

The Maniitsoq structure was a proposed 3 billion-year-old (3 Ga) impact structure located in the Akia terrane of the North Atlantic Craton,[1][2] centred about 55 km (34 mi) south-east of the town of Maniitsoq, Greenland, at 65°15′N 51°50′W / 65.250°N 51.833°W / 65.250; -51.833 (Maniitsoq). However, the Maniitsoq structure has not been widely recognised as an impact structure, and the proposal was criticised for not meeting established criteria for recognising impact craters.[2][3] Furthermore, subsequent studies in the region have demonstrated that there is no evidence for an impact structure, and in fact a number of observations directly contradict the earlier impact structure proposals.[4][5][6][7] The Maniitsoq structure is not recognised as an impact structure by the Earth Impact Database.[8]

Impact structure proposal

Garde et al.

orthogneiss samples suggested to represent rocks melted and hydrothermally altered by the impact.[12]

The proposal was criticised by Reimold et al.

metamorphosed terranes, such as migmatites and inclusion trails in quartz, for shock features, such as microbreccias and planar deformation features.[2][3]

Evidence against an impact

Subsequent studies in the Maniitsoq region demonstrated that deformation in the region continued after the proposed impact age, with major metamorphic and deformation events at ~2.86–2.70 Ga [4] and ~2.55 Ga.[13][14] Extensive deformation was noted both near the proposed impact centre [4] and in ultramafic rocks previously suggested to be post-tectonic.[7][15] Kirkland et al.[4] noted that it was difficult to reconcile the preservation of a circular impact structure and other proposed impact related features with the severe deformation that followed, and instead interpreted the 'impact' features as the result of multiple phases of high-grade metamorphism and partial melting.

Further

stagnant lid processes [6] or an ultra-hot orogenic event.[7] Finally, new dating of the ultramafic intrusions of the Maniitsoq Norite Belt shows that these formed at 3013 Ma, and are therefore too old to have been generated by the impact event.[5][7][15][16]

Further evidence against an impact origin comes from analyses of

oxygen isotopes within the ultramafic intrusions of the Maniitsoq Norite Belt,[7] which show no evidence of the widespread hydrothermal alteration asserted to have been caused by the impact.[12] This is supported by geochemical and petrographical observations from the same rocks, which show that most rocks were largely dry, with only limited local hydrothermal alteration occurring adjacent to intrusions of much younger granitic rocks.[7]

Due to the reasons outlined above, the Maniitsoq Structure is widely believed not to have formed due to a giant impact,[8] and is instead interpreted to reflect terrestrial tectonic processes.[2][3][4][5][6][7]

See also

References

  1. ^
    Elsevier Science Direct.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  2. ^
    doi:10.1016/j.epsl.2013.04.014 – via Elsevier Science Direct.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  3. ^
    S2CID 128625029.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  4. ^
    S2CID 135213870.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  5. ^
    S2CID 134027320.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  6. ^
    S2CID 213973363.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  7. ^
    hdl:10023/20744.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  8. ^ a b "Earth Impact Database". www.passc.net. Retrieved 2020-09-30.
  9. doi:10.1016/j.precamres.2014.06.022 – via Elsevier Science Direct.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  10. doi:10.1016/j.tecto.2015.07.028 – via Elsevier Science Direct.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  11. doi:10.34194/geusb.v28.4722.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  12. ^
    S2CID 140675056
    – via Wiley Online Library.
  13. doi:10.1016/j.lithos.2015.01.024 – via Elsevier Science Direct.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  14. S2CID 212817619.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  15. ^ a b Jean-Francois Ravenelle, Lars Weiershäuser, Glen Cole (2017). "Updated Independent Technical Report for the Maniitsoq Nickel-Copper-Cobalt-PGM Project, Greenland". North American Nickel Technical Report: 1–187.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. S2CID 225197407 – via Cambridge University Press.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
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