The physical nature of granitic magmas: a case of missing information

Abstract

Although there is some considerable understanding of the guiding chemical controls of the granite system, little is known with certainty about the rheology of granitic magmas: a gap in our knowledge that needs to be filled if only to underpin the advanced geochemical models of today. However, we do know that such magmas are highly polymerized, consisting of networks of discrete molecular units: also that their viscosity is strongly dependent on the proportion of bridging atoms — bridges that are broken in the presence of volatiles such as fluorine, chlorine, boron and water so as to drastically lower the viscosity. Furthermore, we continue to learn of other influences such as the effect of the degree of oxidation, as described by Scaillet and his colleagues in 1995, and the effect of the differing associations of the water molecules, as reported by Holtz and others in that same year.