Linking mantle plumes, large igneous provinces and environmental catastrophes

The geology of large-scale volcanism The Siberian Traps, a large region of volcanic rock produced more than 200 million years ago by a massive volcanic event, is a prime example of a large igneous province (LIP). Stephan Sobolev and colleagues present petrological evidence for a large amount of dense recycled oceanic crust in the head of the plume that was responsible for forming the Siberian Traps. Using this, they develop a thermomechanical model that predicts the observed lack of pre-magmatic uplift or lithospheric extension in the region. The model also indicates that massive degassing of carbon dioxide and hydrogen chloride from the plume could alone trigger a mass extinction, and predicts it happening before the main volcanic phase, in agreement with stratigraphic and geochronological data for the Siberian Traps and other LIPs. Large igneous provinces (LIPs) are known for their rapid production of enormous volumes of magma (up to several million cubic kilometres in less than a million years) 1 , for marked thinning of the lithosphere 2 , 3 , often ending with a continental break-up, and for their links to global environmental catastrophes 4 , 5 . Despite the importance of LIPs, controversy surrounds even the basic idea that they form through melting in the heads of thermal mantle plumes 2 , 3 , 6 , 7 , 8 , 9 , 10 . The Permo-Triassic Siberian Traps 11 —the type example and the largest continental LIP 1 , 12 —is located on thick cratonic lithosphere 1 , 12 and was synchronous with the largest known mass-extinction event 1 . However, there is no evidence of pre-magmatic uplift or of a large lithospheric stretching 7 , as predicted above a plume head 2 , 6 , 9 . Moreover, estimates of magmatic CO 2 degassing from the Siberian Traps are considered insufficient to trigger climatic crises 13 , 14 , 15 , leading to the hypothesis that the release of thermogenic gases from the sediment pile caused the mass extinction 15 , 16 . Here we present petrological evidence for a large amount (15 wt%) of dense recycled oceanic crust in the head of the plume and develop a thermomechanical model that predicts no pre-magmatic uplift and requires no lithospheric extension. The model implies extensive plume melting and heterogeneous erosion of the thick cratonic lithosphere over the course of a few hundred thousand years. The model suggests that massive degassing of CO 2 and HCl, mostly from the recycled crust in the plume head, could alone trigger a mass extinction and pr