Linking granulites, intraplate magmatism, and bi-mineralic eclogites with a thermodynamic-petrological model of melt-solid interaction at the base of anorogenic lower continental crust

Archaean continental crust formed from mafic cumulates

“…Of all possible source lithologies that TTGs may derive from, only mafic plagioclase cumulates fit the requirements of having sufficiently high La/Sm and Sm/Yb, and Eu N /Eu*. Such rocks may represent primary gabbro(-norites) or hybridised rocks formed by the interaction between lower-crustal pyroxene-plagioclase granulites and picritic melts 34 . Melt modelling confirms that single-stage melting at different degrees of sources with compositions typical of gabbroic or gabbro-noritic rocks can explain all compositional characteristics of low- F TTGs, without requiring additional processes such as multi-stage accumulation and hybridisation 30 (Supplementary Note 3 ).…”

“…Extensive melt extraction from the gabbroic crustal roots does not go without consequence and can be considered as the prerequisite for the sanukitoid and K-rich granite magmatism that typically follows TTG magmatic episodes 13 . Melt extraction from the mafic lower crust leaves dense eclogitic residues that will founder into the mantle 3 , 21 , 34 , 60 , 61 (Fig. 4c ), which may explain the presence of eclogites in the mantle absent of subduction 3 , 34 .…”

“…Melt extraction from the mafic lower crust leaves dense eclogitic residues that will founder into the mantle 3 , 21 , 34 , 60 , 61 (Fig. 4c ), which may explain the presence of eclogites in the mantle absent of subduction 3 , 34 . Supporting the link between these eclogites and TTGs is the observation that such eclogites, like the cumulate source rocks of TTGs, typically exhibit positive Eu anomalies 62 .…”

“…Some TTG source rocks display cumulate textures, which could indicate a gabbroic rather than basaltic protolith 33 . Alternative source rocks, which could equally explain the compositional features of TTGs, include bimineralic eclogites formed by the interaction between mafic lower crust and picritic melts 34 , and hybridised peridotites residing in the metasomatised lithospheric mantle 35 .…”