Introduction

It is a pleasure to contribute to a volume honoring the late Academician Korzhinskii. He has made major advances to our knowledge of volatile components, not only in systems undergoing metasomatic changes, but in igneous systems as well. Although our understanding of melting and the role of fluids has increased noticeably in recent years, significant gaps remain in our understanding of the melting behaviors of the feldspars and most of the other rock-forming minerals, not only at high pressures, but at atmospheric pressure as well. Largely missing is a knowledge of the temperatures of the solidi and the liquidi. Also unknown in any detail are the structures, thermal properties, and physical properties of the liquids in equilibrium with crystals. Methods such as calorimetry and spectroscopy have not been used to study liquids in situ at elevated pressures. In this paper, we will consider our use of phase equilibria in chemically simple systems to shed light on the structural and thermal properties of magmas.

Experimental methods

One sample of anorthite (sample B) was synthesized from gel, prepared using the method of W.C. Luth & Ingamells (1965) and crystallized hydrothermally at 5 kbar, 1050 °C for at least 48 hours. Another was crystallized from a glass synthesized from oxide reagents, the analysis of which is in Table 13.1 (sample Sc). Synthetic sanidine (sample Ss) was similarly prepared from glass and crystallized at 2 kbar, 700 °C for 30 days (see Table 13.1).