Tectonic model (IMAGE)
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The left part shows the >3230 Ma TTGs formed by melting of intracrustal mafic rocks with no involvement of supracrustal sediments or low-temperature altered basalts. Compressional tectonics took place at ca. 3230 Ma and allowed recycling of supracrustal materials in deep crust due to crustal thickening or proto-subduction. The subsequent melting of supracrustal materials and mafic rocks within a partly thickened lithosphere generated the ≤3230 Ma TTGs with systematically elevated oxygen isotopes.
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