Pilbara Craton

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Pilbara Craton
Stratigraphic range: Age Archean[1]
Satellite view in 2013 of Pilbara Craton
TypeGeological formation
AreaEstimated 250,000 km2 (97,000 sq mi),[1] Pilbara IRBA v7 region 178,231.26 km2 (68,815.47 sq mi)[2]
Thicknessup to 20 km (12 mi)
Lithology
PrimaryGranite
OtherGreenstone
Location
RegionWestern Australia
CountryAustralia
Type section
Named forPilbara
Named bySee Pilbara#Etymology

Map of Australia with the Pilbara region highlighted in red.
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KEY
Pilbara Craton subregions:
PIL01 -
Chichester
PIL02 -
Fortescue
PIL03 -
Hamersley
PIL04 -
Roebourne
Carnarvon subregion:
CAR01 -
Cape Range
Gascoyne subregion:
GAS01 -
Ashburton
continental lithosphere using version 7 of IBRA classification
. The geo-ecosystems of the PIL02(Fortescue) area in particular are usually on much younger exposed rock formations (< 1.7 Ga) than the lithology discussed in this article.

The Pilbara Craton is an old and stable part of the

continental lithosphere located in the Pilbara region of Western Australia
.

The Pilbara Craton is one of only two pristine

Ga (billion years ago) crusts identified on the Earth, along with the Kaapvaal Craton in South Africa. The youngest rocks are 1.7 Ga old in the historic area assigned to the Craton.[1] Both locations may have once been part of the Vaalbara supercontinent or the continent of Ur
.

There are two subregional geographical classification regimes used, being:

  1. The Interim Biogeographic Regionalisation for Australia based upon interacting geo-ecosystems
  2. Based on geology alone where the eastern continuous oldest portion is called the Eastern Pilbara Craton and younger surface lithologies within the larger craton have different names.
The currently exposed continuous Pilbara Craton in red, the Eastern Pilbara region outlined in blue, and detail of local lithologies. However this map does not show other discontinuous exposed oldest rocks of the Pilbara Craton. Accordingly a reader should refer to the references for more detailed geological mapping which is not reproduced here for copyright reasons.

Geology

Main article: Eastern Pilbara Craton

The most important part of the Pilbara Craton to understand the early Earth crust is called the Eastern Pilbara Craton, where still exposed today, are crustal rocks that are up to 3.8 billion years old and intrusive granitic domes along with greenstone belts that are about 3.5 to 3.2 billion years old.[1] The geology was reassessed in 2007 with the separation out from the geologically named Pilbara Craton of a thick succession of interbedded clastic or chemical sedimentary rocks and volcanic rocks forming the Fortescue, Hamersley, and Turee Creek basins that are usually aged from 2.78–2.42 billion years old and the younger volcano-sedimentary Ashburton Basin aged from 2.21–1.79 billion years ago.[1] A surface region between the Fortescue and Hamersley basins is even younger, at less than 1.7 billion years old, as are the surrounding geo-ecosystems surface rocks to the Pilbara Craton. It is important to note that to the east and south of the Eastern Pilbara Craton there are significant outcrops of the very old rocks and that these are confined to the traditional area of the Pilbara Craton which is inferred to be subsurface for more than half its area.[1]

Mineralogy

There are extensive high quality iron ore deposits and also economic to mine gold, silver, copper, nickel, lead, zinc, molybdenum, vanadium and fluorite deposits.[1]

Evidence of earliest life

Evidence of the

haematite alteration that may have been microbially influenced.[7]

A specimen of Apex chert.
Apex chert

The earliest direct evidence of

microfossils to be hydrothermal[14][15] and this is widely supported.[16][17][18][19] Consequently, many alternative abiotic explanations have been proposed for the filamentous microstructures including carbonaceous rims around quartz spherules and rhombs,[14][15] witherite self-assembled biomorphs[20] and haematite infilled veinlets.[21] The carbonaceous matter composing the filaments has also been repeatedly examined with Raman spectroscopy[14][22][21] which has yielded mixed interpretations of results and is therefore regarded by many to be unreliable for determining biogenicity when used alone.[23][24] Perhaps the most compelling argument to date is based on high spatial resolution electron microscopy like scanning and transmission electron microscopy.[19] This study concludes that the nano-scale morphology of the filaments and the distribution of the carbonaceous matter are inconsistent with a biological origin for the filaments. Instead, it is more likely that the hydrothermal
conditions have assisted in the heating, hydration and exfoliation of potassium micas on which barium, iron and carbonate have secondarily been adsorbed.

Carbonaceous structures appearing to be of biological origin have also been discovered in the 3.47 billion year-old Mount Ada Basalt, a rock layer that is a few million years older than the Apex chert. However, the biogenicity of these supposed fossils has also been disputed, with some studies finding abiotic processes to be a more likely culprit for their formation.[11]

Additional potential bioindicators from the Precambrian have been found in the region, including carbonaceous

microfossils in the northeastern Pilbara Craton.[25]

See also

References

  1. ^
    doi:10.18814/epiiugs/2012/v35i1/028
    .
  2. ^ "CAPAD 2014". Retrieved 1 April 2023.
  3. PMID 28486437
    .
  4. ^ "Dresser Formation - Pilbara". pilbara.mq.edu.au.
  5. PMID 24205812
    .
  6. ^ Staff (9 May 2017). "Oldest evidence of life on land found in 3.48-billion-year-old Australian rocks". Phys.org. Retrieved 13 May 2017.
  7. doi:10.1016/j.precamres.2008.07.003
    . Retrieved 30 December 2022.
  8. University of Wisconsin-Madison
    . Retrieved 27 December 2017.
  9. PMID 29255053
    .
  10. PMID 16754604
    .
  11. ^
    S2CID 207986473
    .
  12. PMID 11539686
    .
  13. S2CID 2109914
    .
  14. ^
    S2CID 819491
    .
  15. ^
    ISSN 0301-9268
    .
  16. ISSN 0012-8252
    .
  17. ISSN 1752-0908
    .
  18. ISSN 1342-937X
    .
  19. ^
    ISSN 1342-937X
    .
  20. S2CID 12117608
    .
  21. ^
    S2CID 55506242
    .
  22. S2CID 4382712
    .
  23. PMID 14987478
    .
  24. S2CID 129380309
    .
  25. doi:10.1016/j.precamres.2009.02.004
    .

Bibliography

External links

Wikimedia Commons has media related to Pilbara Craton.
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