Titanium isotopes constrain a magmatic transition at the Hadean-Archean boundary in the Acasta Gneiss Complex

Sarah M Aarons; Jesse R Reimink; Nicolas D Greber; Andy W Heard; Zhe Zhang; Nicolas Dauphas

doi:10.1126/sciadv.abc9959

Titanium isotopes constrain a magmatic transition at the Hadean-Archean boundary in the Acasta Gneiss Complex

Sci Adv. 2020 Dec 9;6(50):eabc9959. doi: 10.1126/sciadv.abc9959. Print 2020 Dec.

Authors

Sarah M Aarons^{1

2}, Jesse R Reimink^{3

4}, Nicolas D Greber⁵, Andy W Heard⁶, Zhe Zhang⁶, Nicolas Dauphas⁶

Affiliations

¹ Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA. [email protected].
² Scripps Institution of Oceanography, University of California, San Diego, San Diego, CA 92037, USA.
³ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA.
⁴ Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA.
⁵ Institute for Geological Sciences, University of Bern, 3012 Bern, Switzerland.
⁶ Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.

Abstract

Plate subduction greatly influences the physical and chemical characteristics of Earth's surface and deep interior, yet the timing of its initiation is debated because of the paucity of exposed rocks from Earth's early history. We show that the titanium isotopic composition of orthogneisses from the Acasta Gneiss Complex spanning the Hadean to Eoarchean transition falls on two distinct magmatic differentiation trends. Hadean tonalitic gneisses show titanium isotopic compositions comparable to modern evolved tholeiitic magmas, formed by differentiation of dry parental magmas in plume settings. Younger Eoarchean granitoid gneisses have titanium isotopic compositions comparable to modern calc-alkaline magmas produced in convergent arcs. Our data therefore document a shift from tholeiitic- to calc-alkaline-style magmatism between 4.02 and 3.75 billion years (Ga) in the Slave craton.

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