Predicted and observed free-air gravity anomalies for delamination models of the formation of the Siberian Flood Basalts

Abstract

The mechanism responsible for the formation of the Siberian Flood Basalts (SFB) has yet to be discovered and adequately quantified. One theory proposes that thinning of the lithosphere due to delamination triggered the eruption. This model is characterized by a drip of denser material within the mantle, and because it involves a density-driven process, calculations of predicted gravity at the surface can be used to test the model. Temperature, composition, and stress output from the delamination model presented in Elkins-Tanton (2007) were used to calculate predicted gravity measurements at the surface. These predictions were then compared to gravity observations of the SFB, focusing on the potential eruptive center at Noril'sk. Model runs in both Cartesian and axisymmetric coordinates were analyzed, and each run predicted a negative anomaly over the site of the drip with a magnitude ranging from 20 to 50 mGal. In the observations, an average radial gravity profile centered on Noril'sk also contained a slight negative anomaly at the center, suggesting partial agreement with the delamination theory. Because the amplitude of the observed gravity anomaly is substantially smaller than the predicted amplitude, the qualitative agreement is encouraging, but not definitive.