Mantle waves and their impact on biogeochemical cycles
Wednesday, November 13, 2024 @ 1 pm in CSL 422
watch Tom’s talk
Abstract
The plate tectonic cycle regulates the carbon cycle and
climate over time via volcanic outgassing and silicate weathering. To quantify
the influence of multiple tectonic processes on global chemical weathering, we
developed the ‘Earth Network’: a Bayesian network capable of modelling joint
conditional dependencies (that is, how processes combine to influence the
system’s state). We find that continental fragmentation plays an important role
in the weathering cycle, with its influence peaking tens of millions of years
after continental breakup. This delayed influence can plausibly be explained by
the new paradigm of ‘mantle waves’ — chains of Rayleigh-Taylor instabilities
that originate during rifting and propagate continentward along lithospheric
keels. These waves convectively remove the lowermost tens of kilometres of
lithosphere, triggering isostatic uplift and denudation of cratonic regions
that have otherwise remained stable for much of Earth’s history. We demonstrate
how this process drives plateau formation via substantial erosion, long after
continental breakup is complete. Using tectonic and biogeochemical models, we
show that this mechanism could also be responsible for driving a succession of
oceanic anoxic events during the Cretaceous. Crucially, the underlying physical
processes were common to other supercontinent cycles (and rifted margins of
Gondwana), thereby profoundly influencing continental erosion, weathering and
climate state through geologic time.