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

Robert H. Smithies (), Yongjun Lu, Tim E. Johnson, Christopher L. Kirkland, Kevin F. Cassidy, David C. Champion, David R. Mole, Ivan Zibra, Klaus Gessner, Jyotindra Sapkota, Matthew C. De Paoli and Marc Poujol
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Robert H. Smithies: Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety
Yongjun Lu: Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety
Tim E. Johnson: School of Earth and Planetary Sciences, The Institute for Geoscience Research (TIGeR), Centre for Exploration Targeting - Curtin Node, Space Science Technology Centre, Curtin University
Christopher L. Kirkland: School of Earth and Planetary Sciences, The Institute for Geoscience Research (TIGeR), Centre for Exploration Targeting - Curtin Node, Space Science Technology Centre, Curtin University
Kevin F. Cassidy: Bare Rock Geological Services Pty Ltd
David C. Champion: Geoscience Australia
David R. Mole: Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth Sciences, The University of Western Australia
Ivan Zibra: Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety
Klaus Gessner: Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety
Jyotindra Sapkota: Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety
Matthew C. De Paoli: Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety
Marc Poujol: Univ Rennes, CNRS, Géosciences Rennes - UMR 6118

Nature Communications, 2019, vol. 10, issue 1, 1-12

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

Date: 2019
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DOI: 10.1038/s41467-019-13547-x

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