Computer Simulations of Magma Chamber Evolution : Testing an Alternative Model for the Development of Layered Mafic Intrusions and the Origin of Granite

Abstract

The association of granite and basalt is observed in every large basaltic magma chamber. Large basaltic rock bodies (termed LMIs, for Layered Mafic Intrusions) provide unique insights into the evolution of the material that makes up over 75% of the Earth?s crust. Yet, the details of LMI evolution remain obscure and controversial. For example, many studies of the well-exposed Skaergaard Intrusion in Greenland document a relatively simple, closed-system evolution in which a single vat of magma progressively crystallized from the outside in. However, the compositions of individual rock layers do not represent realistic magma compositions, and the average composition of the entire intrusion is significantly more mafic (i.e., poor in SiO2) than the initial basaltic melt preserved on the chilled margins of the intrusion. Here, we test the viability of an alternative model that can explain this paradox.