In defense of magmatic diapirs

Abstract

Diapirism as a crustal magma ascent mechanism has been recently criticized. We contend that this reflects an overly simplistic view that diapirs must resemble modeled hot-Stokes diapirs and the perception that magma ascent in dikes is a more problem-free mechanism for the construction of plutons. We describe four Cordilleran plutons that have characteristics much more compatible with diapirs than dike-fed chambers. These plutons were emplaced at depths ranging from ∼10 to 30 km and record different parts of diapiric ascent paths. Most ascended during complex visco-elastic flow of host rock during regional deformation, have narrow structural aureoles indicating power-law behavior of host rock, and were constructed of multiple batches of magma, attributes enabling them to ascend greater distances than single hot-Stokes diapirs. Some features of these plutons are not typically attributed to diapirs, and thus we introduce the term visco-elastic diapir for bodies consisting of one or more batches of magma rising together, with length to width ratios <100, surrounded by host rock deforming by brittle and ductile processes, and for which ascent is driven by buoyancy plus regional stress. We conclude that diapirism remains a valid magma ascent mechanism for the crust.