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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Gurmeet Singh posted an Question
August 07, 2020 • 23:05 pm
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30 points
30 points
- IIT JAM
- Geology (GG)
Sir, please explain 1st point.
The lowest stage has a strong influence of basic rocks. Ihis unit Is believed to represe the relics of the primordial crust i.e. the part of the first formed crust of the earth resltin through the consolidation of the gaseous or molten planet. Ihese rocks are preserved undigested masses or "xenoliths in a vast country of granitic gneisses.
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Sajan sarthak Best Answer
It is representing earth 🌎 when is originated created from gaseous hot molten magma and it was revolving as now so the denswr mass wentdown as core of Fe,Ni . But the crust of early archean earth also known as primordial earth made of felsic less dense material and floated to the top. In today this crust is preserves as xenolith means broken extramagma foreign material in the grantic gneiss bodies.
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sir granitic gneiss represent kr rhi hai today's crust and usme xenoliths representing early Archean rocks fragments. ?
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Mainly the archean cratons are represented by Granitic gneiss..in between them these xenolith are present
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sir , are Archean rocks plutonic?
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Good question.... Variety was there from plutonic to volcanic 🌋
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and sir, can u consider Archean rocks are starting point of formation of crust and then further recycling occurred.
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Yes of course. we age them according to fossil record but archean is free of fossil so perfect dating is done to find out absolute age.
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sir ur message deleted automatically.
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it got clicked
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sir one more thing, wt they are talking about granitic genesis.
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granite when get metamorphosed known as Granitic gneiss
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sir granite rocks bani hogi 1st that we called arechean rocks.. then they metamorphosed, and now original archean rocks get metamorphosed today we only find relics of these original archean as xenolith....?
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is this the situation sir.?
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we find both grantic gneiss and greenstone belts
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Rahul kumar![best-answer]()
The primordial crust on the Earth formed from the crystallization of the surface magma ocean during the Hadean. They are mainly of basic composition. Due to successive recycling of crust, primordial crust isn't found everywhere. They are mainly seen as xenolith in younger rocks.
sir early crust/archean crust is of basic composition?
Yes, primordial crust mainly of basic composition however, there are a few evidences (like presence of zircon) suggesting felsic nature of primordial crust.
and sir wt they are talking about "protogeosyncline were formed over basement of granitic rocks".
mentioned in my question pic.
Protogeosynclines are primitive geosynclines (a type of sedimentary basin) formed during Archaean time. After setting up of atmospheric conditions, early formed primitive crustal rocks got eroded by weathering agents (wind, sea etc.) and subsequently, eroded sediments got deposited in protogeosynclines.