No evidence for high-pressure melting of Earth’s crust in the Archean.

R.H. Smithies (1) , Y. Lu , T. Johnson , C. Kirkland , K. Cassidy , D. Champion , D. Mole , I. Zibra, , K. Gessner (2) , Janak Sapkota (3) , M de Paoli , Marc Poujol (4)

1 Geological Survey of Western Australia
2 School of Earth and Geophysical Sciences [Crawley]
3 MU - University of Leoben
4 GR - Géosciences Rennes

Much of the present-day volume of Earth’s continental crust had formed by the end of theArchean Eon, 2.5 billion years ago, through the conversion of basaltic (mafic) crust into sodicgranite of tonalite, trondhjemite and granodiorite (TTG) composition. Distinctive chemicalsignatures in a small proportion of these rocks, the so-called high-pressure TTG, are interpretedto indicate partial melting of hydrated crust at pressures above 1.5 GPa (>50 kmdepth), pressures typically not reached in post-Archean continental crust. These interpretationssignificantly influence views on early crustal evolution and the onset of platetectonics. Here we show that high-pressure TTG did not form through melting of crust, butthrough fractionation of melts derived from metasomatically enriched lithospheric mantle.Although the remaining, and dominant, group of Archean TTG did form through melting ofhydrated mafic crust, there is no evidence that this occurred at depths significantly greaterthan the ~40 km average thickness of modern continental crust.

Domains: Geochemistry

R.H. Smithies, Y. Lu, T. Johnson, C. Kirkland, K. Cassidy, et al.. No evidence for high-pressure melting of Earth’s crust in the Archean.. Nature Communications, 2019, 10 (1), pp.Art. n°5559. ⟨10.1038/s41467-019-13547-x⟩. ⟨insu-02390622⟩