The Influence of Damage on Drip Instabilities in Continental Lithosphere

Geological evidence indicates large-volume lithospheric drip instabilities form under regions of continental lithosphere. The large volume of these drips suggests that either the lower lithosphere is volumetrically enhanced or the more rigid upper lithosphere participates in the drip. Previous theoretical models using simple rheologies have been unable to produce large-volume drip instabilities as a self-consistent feature of the Earth. As a result, an ad hoc theory for large-volume drip instabilities has been developed, where volume enhancement of the base of the lithosphere is achieved by invoking the specific tectonic setting for each individual drip instability. Here, we generalize the theory of lithospheric drip instabilities and examine their formation as features that may arise naturally from the thermal and rheological structure of the Earth, rather than specific tectonic forcings. Using a damage rheology realistic for the Earth, we find a large portion of the lithosphere may be excavated and entrained into growing drip instabilities. For a critical amount of damage, the growth is accelerated sufficiently that large-volume drip instabilities may form within geologically feasible timeframes. We therefore suggest large-volume lithospheric drip instabilities may arise independent of tectonic settings through entrainment and excavation of the full lithosphere.