Supracrustal rocks (''supra'' (Latin for "above")) are
rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
s that were
deposited on the existing
basement rock
In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...
s of the
crust, hence the name. They may be further
metamorphosed from both
sedimentary and
volcanic rocks.
The oldest
minerals on Earth are
detrital zircon grains from the
Yilgarn Craton in the
Mesoarchaean (3.2–2.8 Ga)
Jack Hills,
Western Australia dated to up to 4.4 Ga, meaning that granitic
continental crust and probably supracrustal rocks formed during the
Hadean
The Hadean ( ) is a Eon (geology), geologic eon of History of Earth, Earth history preceding the Archean. On Earth, the Hadean began with the Formation of the Earth, planet's formation about 4.54 billion years ago (although the start of the H ...
, within 200 million years of Earth accretion. Most Hadean rocks were probably recycled into the mantle before the end of the eon, however, and such pre-4.0 Ga mineral inclusions, the only traces from the earliest rock formation on Earth, are rare.
The
Acasta orthogneisses of the
Slave Craton, Canada, are regarded to be the oldest rocks on Earth, dated to 4.06 Ga, include
protoliths such as
TTGs,
amphibolite
Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...
,
gabbro,
granite, and
diorite. It is possible that such early Hadean TTGs were a source of
phosphorus for the first oceans and therefore contributed nutrients to the first
abiogenic
A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of p ...
steps of life on Earth.
No
Hadean-aged zircon grains have been identified in the
Nuvvuagittuq Supracrustal Belt in northern Quebec, but amphibolites have been dated to 4.28 Ga while 3.75 Ga-old
banded iron formations indicate the minimum age of the belt. The
Napier Mountains in Antarctica are of similar age.
The
Isua greenstone belt contains the oldest, well-preserved, supracrustals, dated at 3.8–3.7
Ga.
References
Notes
Sources
*
Metamorphic rocks
Sedimentary rocks
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