Sanukitoid
“Ancient high-magnesium granitic rock”
Sanukitoid is a distinctive type of Archean-age (2.5-3.0 billion years old) granitic rock with unusually high magnesium and iron content for a felsic rock. It records a specific period of Earth's geological evolution when the style of magmatism was transitioning from the earliest TTG crust formation to modern-style plate tectonics.
plagioclase, quartz, hornblende (magnesian), biotite, augite, magnetite, alkali feldspar
Superior Province (Canada), Pilbara Craton (Australia), Dharwar Craton (India), Karelian Craton (Finland/Russia), Sanuki region (Japan)
6-7
The global appearance of sanukitoids around 2.7 billion years ago may mark the moment when modern-style subduction began — they could be geological timestamps of one of the biggest transitions in Earth's tectonic history.
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