CONDITIONS FOR TRANSPORT OF PLUTONIC XENOLITHS

Abstract

The authors analysis indicates that the principal factor determining whether xenoliths are transported to the surface is the fluid content in the magma-filled fissure Mafic and ultramafic magmas undersaturated in volatiles are unable to transport even relatively small xenoliths. Conversely, saturated magmas rich in volatiles can transport xenoliths comparable in size to the width of the fracture. As a result of decompression during ascent, a magma that is initially undersaturated in volatiles becomes saturated at some depth, after which it begins to liberate fluid rapidly This causes breakdown of the viscous plug at the tip of the propagating fissure and a considerable increase in the rate of its growth if the concentration of volatiles in the magma is sufficiently high. Above the depth of saturation, the magma then becomes capable of transporting large xenoliths.