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The ¹⁴²Nd/¹⁴⁴Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present

Hyung, Eugenia and Jacobsen, Stein B. (2020) The ¹⁴²Nd/¹⁴⁴Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings of the National Academy of Sciences of the United States of America, 117 (26). pp. 14738-14744. ISSN 0027-8424. https://resolver.caltech.edu/CaltechAUTHORS:20200618-075434777

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Abstract

Early silicate differentiation events for the terrestrial planets can be traced with the short-lived ¹⁴⁶Sm-¹⁴²Nd system (∼100-My half-life). Resulting early Earth-produced ¹⁴²Nd/¹⁴⁴Nd variations are an excellent tracer of the rate of mantle mixing and thus a potential tracer of plate tectonics through time. Evidence for early silicate differentiation in the Hadean (4.6 to 4.0 Ga) has been provided by ¹⁴²Nd/¹⁴⁴Nd measurements of rocks that show both higher and lower (±20 ppm) values than the present-day mantle, demonstrating major silicate Earth differentiation within the first 100 My of solar system formation. We have obtained an external 2σ uncertainty at 1.7 ppm for ¹⁴²Nd/¹⁴⁴Nd measurements to constrain its homogeneity/heterogeneity in the mantle for the last 2 Ga. We report that most modern-day mid-ocean ridge basalt and ocean island basalt samples as well as continental crustal rocks going back to 2 Ga are within 1.7 ppm of the average Earth ¹⁴²Nd/¹⁴⁴Nd value. Considering mafic and ultramafic compositions, we use a mantle-mixing model to show that this trend is consistent with a mantle stirring time of about 400 My since the early Hadean. Such a fast mantle stirring rate supports the notion that Earth’s thermal and chemical evolution is likely to have been largely regulated by plate tectonics for most of its history. Some young rocks have ¹⁴²Nd/¹⁴⁴Nd signatures marginally resolved (∼3 ppm), suggesting that the entire mantle is not equally well homogenized and that some silicate mantle signatures from an early differentiated mantle (>4.1 Ga ago) are preserved in the modern mantle.


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https://doi.org/10.1073/pnas.2006950117DOIArticle
https://www.pnas.org/content/suppl/2020/06/09/2006950117.DCSupplementalPublisherSupporting Information
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Additional Information:© 2020 National Academy of Sciences. Published under the PNAS license. Edited by Donald E. Canfield, Institute of Biology and Nordic Center for Earth Evolution, University of Southern Denmark, Odense M., Denmark, and approved May 1, 2020 (received for review April 15, 2020). PNAS first published June 15, 2020. This work was partially supported by NASA Emerging Worlds Grants NNX15AH66G and 80NSSC20K0346. We thank the four anonymous reviewers whose comments and suggestions greatly improved the manuscript. Some of the samples were provided by Charles Langmuir (KN207-2, CH59-2, A12DR44, and HLY102-096), Bjørn Larsen (K1714), Rita Parai (DICE), and Jonathan Tucker (RC2806 2D-1). Data Availability: Data tables, in addition to the mathematical principles and corresponding MATLAB scripts for processing data, are available in the SI Appendix. In addition, the data will be made available through EarthChem (https://ecl.earthchem.org/view.php?id=1545). Author contributions: E.H. and S.B.J. designed the study. E.H. processed the samples and performed the measurements. E.H. and S.B.J. performed calculations and wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission. Data deposition: Data for this paper have been deposited at EarthChem (https://ecl.earthchem.org/view.php?id=1545). This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2006950117/-/DCSupplemental.
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NASANNX15AH66G
NASA80NSSC20K0346
Issue or Number:26
Record Number:CaltechAUTHORS:20200618-075434777
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200618-075434777
Official Citation:The 142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Eugenia Hyung, Stein B. Jacobsen. Proceedings of the National Academy of Sciences Jun 2020, 117 (26) 14738-14744; DOI: 10.1073/pnas.2006950117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103965
Collection:CaltechAUTHORS
Deposited By: Thomas Morrell
Deposited On:22 Jun 2020 22:08
Last Modified:01 Jul 2020 16:24

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