page_title: Archean felsic volcanic rocks
section_title: Conflicting compositions
hierarchical_section_title: Archean felsic volcanic rocks / Relationships between Archean felsic volcanic rocks and granitoids / Conflicting compositions
caption_attribution_description: English: AFV Hypotheses. Adopted from Agangi et al. (2018)
context_page_description: Archean felsic volcanic rocks are felsic volcanic rocks that were formed in the Archean Eon. The term "felsic" means that the rocks have silica content of 62–78%. Given that the Earth formed at ~4.5 billion year ago, 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.
  As the Archean Earth was hotter than the present, formation of felsic volcanic rocks may differ from the modern plate tectonics.
  Archean felsic volcanic rocks are distributed only in the preserved Archean greenstone belts, where deformed sequences of volcanic-sedimentary rocks are common. Felsic volcanic rocks are rare in the early Earth and only contribute to less 20% of rocks in the Archean greenstone belts worldwide. Nonetheless, mafic volcanic rocks occupy about 50% in the greenstone belts. Thus, felsic volcanic rocks are rare members in the Archean terranes.
  Archean felsic volcanic activities commonly occur in submarine environments. The composition of Archean felsic volcanic rocks are equivalent to a spectrum between dacite and rhyolite.
context_section_description: Records of Archean felsic volcanic rocks shows a peculiar trend. The eruption of felsic volcanic rocks and plutonic activities in Archean are largely synchronised as show in overlapping zircon ages. On contrary, the chemical compositions of some felsic volcanic rocks are similar to that of GMS but they are much older than GMS. For example, a GMS-like rhyolite unit in the Abitibi Greenstone Belt (abnormally more enriched in potassium and heavy rare-earth elements than other Archean felsic volcanic rocks) has no plutonic equivalent in the same period. The composition of felsic volcanic rocks are being altered concurrently with shifting granitoid composition.
caption: Fig 5. Possible relationship 1 of Archean felsic volcanic rocks and granitoids. GMS may have intruded the crust at a very shallow depth, and later TTG intruded.[9]
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