Impact events

A Giant Impact Origin For The First Subduction on Earth

By Keith Cowing

Status Report

Geophysical Research Letters

May 8, 2024

Filed under geology, Geophysical Research Letters, Hadean zircon, Impact event, Moon, Moon-forming giant impact, Plate Tectonics, rocky planet, Subduction, tectonics, Zircon

A Giant Impact Origin For The First Subduction on Earth — A schematic illustration of the path from the Moon-forming giant impact (MGI) to plume-induced subduction in the early Hadean. A canonical MGI (a) leads to a two-layered mantle structure with a mostly solid lower mantle and an elevated core-mantle boundary temperature (b) (Deng et al., 2019; Yuan et al., 2023). After solidification of the upper magma ocean within several million years (Hamano et al., 2013; Nikolaou et al., 2019), we assume a proto-lithosphere gradually formed over 50–100 million years (c), which was then destabilized and segmented by a mantle plume from an large low-shear velocity province made of the Theia mantle remnant (Yuan et al., 2023) (d). — Geophysical Research Letters

Hadean zircons provide a potential record of Earth’s earliest subduction 4.3 billion years ago. It remains enigmatic how subduction could be initiated so soon after the presumably Moon-forming giant impact (MGI).

Earlier studies found an increase in Earth’s core-mantle boundary (CMB) temperature due to the accumulation of the impactor’s core, and our recent work shows Earth’s lower mantle remains largely solid, with some of the impactor’s mantle potentially surviving as the large low-shear velocity provinces (LLSVPs).

Here, we show that a hot post-impact CMB drives the initiation of strong mantle plumes that can induce subduction initiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMB temperature is the primary factor triggering early subduction, with enrichment of heat-producing elements in LLSVPs as another potential factor.

The models link the earliest subduction to the MGI with implications for understanding the diverse tectonic regimes of rocky planets.

A Giant Impact Origin for the First Subduction on Earth, Geophysical Research Letters (open access)

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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