Zircons reveal the history of fluctuations in oxidation state of crustal magmatism and supercontinent cycle.

Autor: Wang R; State Key Laboratory of Geological Processes and Mineral Resources, Institute of Earth Sciences, China University of Geosciences, Beijing 100083, China; Frontiers Science Center for Deep-time Digital Earth, China University of Geosciences (Beijing), Beijing 100083, China. Electronic address: rw@cugb.edu.cn., Wu SC; State Key Laboratory of Geological Processes and Mineral Resources, Institute of Earth Sciences, China University of Geosciences, Beijing 100083, China., Weinberg RF; School of Earth, Atmosphere and Environment, Monash University, Clayton VIC 3800, Australia., Collins WJ; The Institute for Geoscience Research, Curtin University, Perth WA 6102, Australia., Cawood PA; School of Earth, Atmosphere and Environment, Monash University, Clayton VIC 3800, Australia.
Jazyk: angličtina
Zdroj: Science bulletin [Sci Bull (Beijing)] 2024 Jan 15; Vol. 69 (1), pp. 97-102. Date of Electronic Publication: 2023 Oct 31.
DOI: 10.1016/j.scib.2023.10.034
Abstrakt: We apply a zircon redox index to a global compilation of detrital zircons to track the variation of oxidation state, expressed as ΔFMQ, through Earth's history. Those from I-type rocks, which comprise mantle and crustal igneous protoliths, including tonalite-trondhjemite-granodiorites (TTGs), generally have a high oxidation state (ΔFMQ > 0). In contrast, zircons from igneous rocks derived from supracrustal source rocks (S-type) are commonly reduced (ΔFMQ < 0). With the probability density function derived from the Gaussian-Kernel-Density-Estimation, we use the maximum likelihood estimation (MLE) to distinguish S-type from I-type zircons through Earth's history using zircon redox. Voluminous S-type magma production shows a ca. 600 Ma cyclicity that is closely related to the supercontinent cycle. We link a cyclic drop in redox values after 2.6 Ga to periodic S-type magma generation associated with burial and melting of metasedimentary rocks during supercontinent assembly and amalgamation. The ΔFMQ of the detrital zircons rise at ∼3.5 Ga followed by a consistent average ΔFMQ > 0 over the last 3 Ga. Given that the redox state of magmas is independent of crustal thickness and silica variation, and elevated values are likely more closely related to tectonic setting, we suggest that the consistent average ΔFMQ > 0 from ca. 3.5 Ga onwards relates to recycling of oceanic lithosphere back into the mantle in what eventually became established as subduction zones. The more reduced magmas associated with sedimentary sources, became established at 2.6 Ga, presumably in response to continental rocks rising above sea-level, and follow peaks of productivity associated with the supercontinent cycle.
Competing Interests: Conflict of interest The authors declare that they have no conflict of interest.
(Copyright © 2023 Science China Press. Published by Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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