Experimental strategies for the investigation of low temperature properties in granitic and pegmatitic melts

Abstract

The physical behavior of silicate melts during the final stages of intrusion in the earth's crust are poorly understood. In particular, the low temperature limit of igneous petrogenesis is poorly constrained. The extreme differentiates of granitic magmatism that lead to pegmatite genesis span a very large range of composition not normally considered to be within the domain of igneous melt compositions. This combination of very low petrogenetic temperatures and extreme chemistries requires a concentrated effort for the determination of melt properties under conditions of pressure, temperature and composition appropriate to these systems. An experimental strategy for the determination of melt properties under appropriate conditions is presented. The determination of individual melt properties at very low temperatures is described with the aid of three examples, heat capacity, volume and viscosity. In this way the physical behavior of an important component of the earth's crust will become accessible.

Granite and granitic pegmatite melts: volumes and viscosities

“…Thus studies of the water-free system just above the glass transition temperature can be used as constraints on the properties of such melts at the temperatures of interest. Redrawn from Dingwell (1993). and viscosities for granitic melts in the temperature and pressure range pertinent to the crystallisation of specialised granites and their derivative pegmatites requires a different approach, one that has more in common with solid state methods of materials characterisation than with traditional liquid state methods.…”

“…Granitic melts are good glass-formers. Thus the metastable extension of liquid properties below the melting point (or liquidus) into the supercooled liquid regime can be studied extensively without the disturbance of incipient crystallisation (Dingwell 1993).…”