Introduction

‘Pyrolite’ was chosen by Ringwood (1962a,b) as the name for a model chemical composition for the mantle, consisting predominantly of pyroxene and olivine. Subsequently, the pyrolite concept has been quantified, and assessment of model pyrolite compositions has been a major theme in experimental studies at The Australian National University and the University of Tasmania. Such experimental studies have been designed to achieve an understanding of the mineralogy of the upper mantle, the transition zone, and the lower mantle as a function of pressure and temperature and to investigate the melting behaviour and melt products of the upper mantle to depths of approximately 150 km. The purpose of this chapter is to review the experimental studies of pyrolite compositions relevant to the Earth's upper mantle and to summarize the applications of such studies.

We shall begin with the definition of pyrolite in its historical context before presenting a review of the experimental studies (both published and ongoing) that have been performed on a range of different pyrolite compositions. These experimental studies have emphasized the very important influence of volatile (C + H + O) composition on the solidus position (the pressure–temperature conditions at which melt first appears). The experimental findings have led directly to models for the upper mantle that predict distinctive sub-solidus mineralogies and melting characteristics in particular tectonic environments. In the final part of this chapter we shall consider the petrological constraints on magma genesis based on the pyrolite concept and the findings from the experimental studies.