Earth’s evolving geodynamic regime recorded by titanium isotopes

Deng, Zhengbin, Schiller, Martin, Jackson, Matthew G., Millet, Marc-Alban ORCID: https://orcid.org/0000-0003-2710-5374, Pan, Lu, Nikolajsen, Katrine, Saji, Nikitha S., Huang, Dongyang and Bizzarro, Martin 2023. Earth’s evolving geodynamic regime recorded by titanium isotopes. Nature 621 , pp. 100-104. 10.1038/s41586-023-06304-0

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Abstract

Earth’s mantle has a two-layered structure, with the upper and lower mantle domains separated by a seismic discontinuity at about 660 km (refs. 1,2). The extent of mass transfer between these mantle domains throughout Earth’s history is, however, poorly understood. Continental crust extraction results in Ti-stable isotopic fractionation, producing isotopically light melting residues3,4,5,6,7. Mantle recycling of these components can impart Ti isotope variability that is trackable in deep time. We report ultrahigh-precision 49Ti/47Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 billion years ago (Ga) and modern ocean island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052 ± 0.006‰ heavier than the modern upper mantle sampled by normal mid-ocean ridge basalts (N-MORBs). The 49Ti/47Ti ratio of Earth’s upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between approximately 3.5 and 2.7 Ga, establishing that more continental crust was extracted during this epoch. The +0.052 ± 0.006‰ offset between BSE and N-MORBs requires that <30% of Earth’s mantle equilibrated with recycled crustal material, implying limited mass exchange between the upper and lower mantle and, therefore, preservation of a primordial lower-mantle reservoir for most of Earth’s geologic history. Modern OIBs record variable 49Ti/47Ti ratios ranging from chondritic to N-MORBs compositions, indicating continuing disruption of Earth’s primordial mantle. Thus, modern-style plate tectonics with high mass transfer between the upper and lower mantle only represents a recent feature of Earth’s history.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	Nature Research
ISSN:	0028-0836
Date of First Compliant Deposit:	7 July 2023
Date of Acceptance:	9 June 2023
Last Modified:	09 Oct 2023 05:34
URI:	https://orca.cardiff.ac.uk/id/eprint/160847

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