Abstract
Abstract The growth and recycling of continental crust has resulted in the chemical and thermal modification of Earth’s mantle, hydrosphere, atmosphere, and biosphere for ∼4.0 b.y. However, knowledge of the protolith that gave rise to the first continents and whether the environment of formation was a subduction zone still remains unknown. Here, tonalite melts are formed in high P-T experiments in which primitive oceanic plateau starting material is used as an analogue for Eoarchean (3.6–4.0 Ga) oceanic crust generated at early spreading centers. The tonalites are produced at 1.6–2.2 GPa and 900–950 °C and are mixed with slab-derived aqueous fluids to generate melts that have compositions identical to that of Eoarchean continental crust. Our data support the idea that the first continents formed at ca. 4 Ga and subsequently, through the subduction and partial melting of ∼30–45-km-thick Eoarchean oceanic crust, modified Earth’s mantle and Eoarchean environments and ecosystems.
Highlights
The mechanisms responsible for generating the first continents and evidence for the beginning of plate tectonics beneath liquid water oceans remain topics of substantial debate (Dhuime et al, 2015; Foley et al, 2002; Moyen and Martin, 2012; Nutman et al, 2012; Rapp et al, 2003; Smart et al, 2016)
Up to 90% of juvenile Eoarchean (3.6–4.0 Ga) continental crust is composed of plagioclase-rich tonalite, trondjhemite, and granodiorite (TTG) granitoids (Foley et al, 2002; Hoffmann et al, 2011; Martin et al, 2005; Nutman et al, 2009; Polat and Hofmann, 2003; Rapp et al, 2003)
Determining how these TTG rocks are generated is key to identifying what protolith(s) gave rise to the first silicic nuclei, understanding what planetary-scale tectonic processes were operating on the early Earth, and how continent formation could have modified Eoarchean environments and primitive ecosystems (Kamber, 2010; Nutman et al, 2012; Wordsworth and Pierrehumbert, 2013)
Summary
The mechanisms responsible for generating the first continents and evidence for the beginning of plate tectonics beneath liquid water oceans remain topics of substantial debate (Dhuime et al, 2015; Foley et al, 2002; Moyen and Martin, 2012; Nutman et al, 2012; Rapp et al, 2003; Smart et al, 2016). Previous experiments on a range of metabasic rocks (amphibolite and eclogite) and compositions (MORB and island arc) have not generated partial melts with major and trace element compositions and geochemical patterns similar to ETTG
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