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Impact-driven tectonism during the Hadean

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Impacting was one of the dominant processes in shaping planetary surfaces in the early solar system evolution. While its effects on volcanism and crustal evolution of other planetary bodies has been well documented, its effects on early Earth dynamics remain poorly constrained, largely due to dearth of data from the Hadean. It has speculated that impacts may have contributed to the development of active tectonics and subduction, but the physical interactions between large impacts and mantle dynamics are poorly understood. Here we introduce a model of mantle convecting incorporating the thermo-physical response of large impacts on the mantle. Our simulations track the tectonic evolution of an evolving early Earth, beginning immediately post-magma ocean, through the Hadean. Our simulations show that giant impacts in the Hadean both weaken the lithosphere, and create a large thermal anomaly in the mantle. These factors may be capable of driving transient tectonic activity and subduction. Our preferred models demonstrate waning tectonic activity with diminishing impact flux from 4.5-4.3Ga, a lull in tectonic activity from ~4.3-4.1Ga, and a resurgence of activity at ca. 4.1Ga due to the effect of a thick, negatively dense subductable lithosphere, and increased impact flux at this time. We have simulation a parameterised evolution of the core in these models, and track the magnetic field strength, as well as the evolution of mantle and crustal melting. We compare the predictions of our models with existing zircon, paleointensity, and geochemical datasets.

This talk is part of the Occasional Earth Science Seminars series.

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