Fig. 4: Model of continental nuclei formation by intracrustal melting of mafic protocrust and subsequent melt differentiation during the late Hadean to early Archean.
From: Incipient continent formation by shallow melting of an altered mafic protocrust
The circulation of hydrothermal seawater (blue arrows) through faults and fractures (black lines) in the ancient protocrust produces rocks with low δ18O compositions. Subsequent burial and/or heating of this altered protocrust produce tonalitic partial melts (magmas) with low δ18O compositions (orange and yellow polygons). Note that spatial variations in bulk crustal composition (e.g., XFeO) and geotherm may result in both garnet-absent and garnet-present melting. Garnet-present melting will form low-pressure to medium-pressure TTG melts and where geotherms are locally high enough, garnet-absent melting may generate rocks with Icelandite characteristics.
