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Hadean geodynamics inferred from time-varying 142Nd/144Nd in the early Earth rock record

Saji, N.S., Larsen, K., Wielandt, D., Schiller, M., Costa, M.M., Whitehouse, M.J., Rosing, M.T. and Bizzarro, M. 2018. Hadean geodynamics inferred from time-varying 142Nd/144Nd in the early Earth rock record. Geochemical Perspectives Letters 7 , pp. 43-48. 10.7185/geochemlet.1818

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Abstract

Tracking the secular evolution of 142Nd/144Nd anomalies is important towards understanding the crust-mantle dynamics in the early Earth. Excessive scatter in the published data, however, precludes identifying the fine structure of 142Nd/144Nd evolution as the expected variability is on the order of few parts per million. We report ultra-high precision 142Nd/144Nd data for Eoarchean and Palaeoarchean rocks from the Isua Supracrustal Belt (SW Greenland) that show a well-resolved 142Nd/144Nd temporal variability suggesting progressive convective homogenisation of the Hadean Isua depleted mantle. This temporally decreasing 142Nd/144Nd signal provides a direct measure of early mantle dynamics, defining a stirring timescale of <250 Myr consistent with vigorous convective stirring in the early mantle. The 142Nd/144Nd evolution suggests protracted crustal residence times of ~1000-2000 Myr, inconsistent with modern-style plate tectonics in the Archean. In contrast, a stagnant-lid regime punctuated by episodes of mantle overturns accounts for the long life-time estimated here for the Hadean proto-crust.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: European Association of Geochemistry
ISSN: 2410-339X
Date of First Compliant Deposit: 7 January 2019
Date of Acceptance: 23 July 2018
Last Modified: 07 Jan 2019 11:45
URI: http://orca.cf.ac.uk/id/eprint/118078

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