Drip instabilities of continental lithosphere: Acceleration and entrainment by damage

Abstract

Geological evidence indicates large-volume lithospheric drip instabilities form under regions of continental lithosphere. The size of these drips suggests that either the base of the lithosphere is volumetrically increased or the highly viscous upper lithosphere participates in the drip. Previous theoretical models using simple rheologies have been unable to produce unforced large-volume drip instabilities. Thus large drip instabilities are typically induced by thickening or destabilizing the mobile base of the lithosphere through tectonic forcing, such as convergent thickening or dense magmatic emplacement following extension. Here, we propose a theory of lithospheric drip instabilities that may arise naturally from the thermal and rheological structure of Earth, independent of specific tectonic forcings. Using damage physics relevant for Earth, we find a large portion of the lithosphere may be mobilized 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 time-frames. We therefore suggest large-volume lithospheric drip instabilities may arise independently of tectonic settings through damage-assisted mobilization and entrainment of the highly viscous lithosphere. © 2012 The Authors Geophysical Journal International © 2012 RAS.