Archean felsic volcanic rocks
Felsic volcanic rocks formed in the Archean Eon / From Wikipedia, the free encyclopedia
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Archean felsic volcanic rocks are felsic volcanic rocks that were formed in the Archean Eon (4 to 2.5 billion years ago).[2] The term "felsic" means that the rocks have silica content of 62–78%.[3] Given that the Earth formed at ~4.5 billion year ago,[4] Archean felsic volcanic rocks provide clues on the Earth's first volcanic activities on the Earth's surface started 500 million years after the Earth's formation.[5]
As the Archean Earth was hotter than the present, formation of felsic volcanic rocks may differ from the modern plate tectonics.[5][6][7]
Archean felsic volcanic rocks are distributed only in the preserved Archean greenstone belts, where deformed sequences of volcanic-sedimentary rocks are common.[5][6][8] Felsic volcanic rocks are rare in the early Earth and only contribute to less 20% of rocks in the Archean greenstone belts worldwide.[6] In contrast, mafic volcanic rocks (such as basalt and komatiite, silicate content <52%[3]) occupy about 50% in the greenstone belts.[6] Thus, felsic volcanic rocks are rare members in the Archean terranes.
Archean felsic volcanic activities commonly occur in submarine environments.[7] The composition of Archean felsic volcanic rocks are equivalent to a spectrum between dacite and rhyolite.[5] They can be distinguished by their mineral assemblages, rock chemistry and rock layer relationship in the sequences.[7]
Archean felsic volcanic rocks are utilised to date the timing of geological events and match distant rock units in separated Archean cratons.[9] They are important to reconstruct Archean geological environments.[10][11]
Felsic granitoids are the most prevalent rock type in Archean terranes.[6] These intrusive felsic igneous rocks include TTG suites (Tonalite-trondhjemite-granodiorite) that contributes over half the portion of Archean cratons.[6] They have implications in finding how the felsic volcanic rocks were formed and related to the granitoids.[9][12]