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An andesitic source for Jack Hills zircon supports onset of plate tectonics in the Hadean.

ABSTRACT: The composition and origin of Earth's early crust remains hotly debated. Here we use partition coefficients to invert the trace element composition of 4.3-3.3 Gyr Jack Hills zircons to calculate the composition of the melts from which they crystallised. Using this approach, the average SiO2 content of these melts was 59?±?6 wt. % with Th/Nb, Dy/Yb and Sr/Y ratios of 2.7?±?1.9, 0.9?±?0.2 and 1.6?±?0.7, respectively. Such features strongly indicate that the protolith for the Jack Hills zircons was not an intra-plate mafic rock, nor a TTG (tondjhemite-tonalite-granodiorite) or a Sudbury-like impact melt. Instead, the inferred equilibrium melts are much more similar to andesites formed in modern subduction settings. We find no evidence for any secular variation between 4.3 and 3.3 Gyr implying little change in the composition or tectonic affinity of the Earth's early crust from the Hadean to Mesoarchaean.

SUBMITTER: Turner S

PROVIDER: S-EPMC7060172 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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An andesitic source for Jack Hills zircon supports onset of plate tectonics in the Hadean.

Turner Simon S Wilde Simon S Wörner Gerhard G Schaefer Bruce B Lai Yi-Jen YJ

Nature communications 20200306 1

The composition and origin of Earth's early crust remains hotly debated. Here we use partition coefficients to invert the trace element composition of 4.3-3.3 Gyr Jack Hills zircons to calculate the composition of the melts from which they crystallised. Using this approach, the average SiO<sub>2</sub> content of these melts was 59 ± 6 wt. % with Th/Nb, Dy/Yb and Sr/Y ratios of 2.7 ± 1.9, 0.9 ± 0.2 and 1.6 ± 0.7, respectively. Such features strongly indicate that the protolith for the Jack Hills ...[more]

PMID: 32144246

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Project description:The development of plate tectonics from a pre-plate tectonics regime requires both the initiation of subduction and the development of nascent subduction zones into long-lived contiguous features. Subduction itself has been shown to be sensitive to system parameters such as thermal state and the specific rheology. While generally it has been shown that cold-interior high-Rayleigh-number convection (such as on the Earth today) favours plates and subduction, due to the ability of the interior stresses to couple with the lid, a given system may or may not have plate tectonics depending on its initial conditions. This has led to the idea that there is a strong history dependence to tectonic evolution-and the details of tectonic transitions, including whether they even occur, may depend on the early history of a planet. However, intrinsic convective stresses are not the only dynamic drivers of early planetary evolution. Early planetary geological evolution is dominated by volcanic processes and impacting. These have rarely been considered in thermal evolution models. Recent models exploring the details of plate tectonic initiation have explored the effect of strong thermal plumes or large impacts on surface tectonism, and found that these 'primary drivers' can initiate subduction, and, in some cases, over-ride the initial state of the planet. The corollary of this, of course, is that, in the absence of such ongoing drivers, existing or incipient subduction systems under early Earth conditions might fail. The only detailed planetary record we have of this development comes from Earth, and is restricted by the limited geological record of its earliest history. Many recent estimates have suggested an origin of plate tectonics at approximately 3.0?Ga, inferring a monotonically increasing transition from pre-plates, through subduction initiation, to continuous subduction and a modern plate tectonic regime around that time. However, both numerical modelling and the geological record itself suggest a strong nonlinearity in the dynamics of the transition, and it has been noted that the early history of Archaean greenstone belts and trondhjemite-tonalite-granodiorite record many instances of failed subduction. Here, we explore the history of subduction failure on the early Earth, and couple these with insights from numerical models of the geodynamic regime at the time.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.

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An andesitic source for Jack Hills zircon supports onset of plate tectonics in the Hadean.

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An andesitic source for Jack Hills zircon supports onset of plate tectonics in the Hadean.

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