Mechanics of active magmatic intraplating in the Rio Grande Rift near Socorro, New Mexico

We investigate long-term deformation due to the Socorro Magma Body (SMB), one of the largest active intrusions in the Earth's continental crust, using interferometric synthetic aperture radar (InSAR) observations and finite element simulations. InSAR data spanning 15 years (1992-2007) indicate that the magma body is associated with a steady crustal uplift at a rate of about 2 mm yr(-1). Previous work showed that while the pattern of surface uplift is consistent with an elastic inflation of a large sill-like magma body, the SMB could not have formed via steady elastic inflation because the latter would be outpaced by magma solidification. We resolve this problem using coupled thermovisco-elastic models, and place constraints on the intrusion history as well as the rheology of the ambient crustal rocks. We demonstrate that observations rule out the linear Maxwell response of the ductile crust, but are consistent with laboratory-derived power law rheologies. Our preferred model suggests that the age of the SMB is of the order of 10(3) years, and that the apparent constancy of the present-day uplift may be due to slow heat transfer and ductile deformation in a metamorphic aureole of a giant sill-like magma intrusion, rather than due to a steady increase in the magma overpressure. The SMB is a contemporaneous example of "magmatic intraplating," a process by which large volumes of mafic melt stall and spread at midcrustal depths due to density or rheology contrasts.