Melt Segregation and Extraction From Deforming Plutons

A solid, interconnected, crystal framework with interstitial melt develops during the late stages of magma crystallization in a pluton. This framework imparts solid characteristics to the magma, which then behaves in ways similar to a migmatite undergoing partial melting. The solid framework allows melt to segregate from its pores, driven by pressure differences imposed in part by density contrasts between solid and melt, and in part by external, tectonic deformation. Segregated melt is strongly fractionated compared to its source and may be extracted from the system to form the fractionated end-members of plutons. This paper describes a number of features such as magmatic shear zones, magmatic boudins with melt in necks, and melt-filled cracks that are frozen indicators of such a process. The nature and orientation of these features are controlled by regional strain axes and can be used to infer their orientation during late pluton cooling.