Plume-induced heat flux anomalies and the associated thinning of the
continental lithosphere
Abstract
While the passage of a plume beneath a thin oceanic lithosphere is
usually connected to a hot spot track, and thus can easily be traced
back in time, the interaction between a plume and thick continental or
cratonic lithosphere is less obvious. Although volcanic eruptions are a
common feature for plumes reaching the surface beneath continents,
especially in the form of large igneous provinces associated with the
arrival of a plume head, it is unlikely that the entire plume track is
marked by extrusive volcanism. The thickness of continental lithosphere,
and especially cratonic lithosphere, may prohibit the eruption of magma
in many places, and can re-focus extrusive volcanism towards places
where the lithosphere is thinner or more permeable due to preexisting
fault structures. However, even though no magma might be erupted, the
passage of a continent over a hot mantle upwelling will be visible in
the surface heat flux, even millions of years after the plume passage.
In this study, we use numerical models to investigate how a plume
passing beneath continental or cratonic lithosphere affects surface heat
flux over time, and which parameters of the plume and subsurface
structure are the most relevant for determining the size of the
respective heat flux anomaly. We show that any kind of surface heat flux
anomaly is associated with an erosional thinning of the base of the
lithosphere, and greater thinning leads to larger heat flux anomalies.
While the maximum of lithosphere thinning is observed at a position and
time a few million years after the plate passes over the plume, heat
flux anomalies related to conduction continue to increase, reaching a
maximum about 80-150 Myr after passage over the plume. In the case of
stagnant (stationary) plates, the delays between lithosphere thinning
and heat flux anomaly are smaller and the observed anomalies are larger.
Amplitudes of both thinning and heat flux anomalies are most sensitive
to the viscosity of the asthenosphere and the lower lithosphere, because
a lower viscosity facilitates basal erosion and thus increases heat
fluxes. Also important are the interaction time between plume and plate,
i.e. plate velocity or plume life time, and the plume strength / excess
temperature. These results have important implications for understanding
plume-lithosphere interactions in polar settings, e.g. Greenland and
Antartica, and for various places in Africa, North America and China.