The composition of mantle-derived magmas suggest a remarkable variety in the abundances of volatiles in the upper mantle. Volatile components like H2O and CO2, generally depress the melting point of mantle considerably (Green, 2015). However, we have little knowledge about these first, incipient melts. We know incipient melts exist in a large temperature range (~300°C) in the upper mantle, but the chemical compositions of these melts are poorly constrained, and therefore the effect of volatiles on the various melt proportions could change the behaviour of melt significantly (Foley et al., 2011).
Nature provides us with limited samples of primitive mantle-derived melts, which have mostly suffered fractionation or weathering processes. Therefore it is necessary to simplify the picture for studying the primitive melts. Experimental petrology provides better insights into the incipient melting regime in mantle conditions. This project consists of a systematic study to determine the chemistry of incipient melts using different starting compositions (Green, 2015) with various volatile compositions (CO2 and H2O). We are considering the effects of temperature (provide T range), and pressure (provide P range) in the incipient melt regime using piston cylinder apparatus. Our results show that melt compositions progress from carbonate-rich to carbonated silicate and are characterised by strong increase in SiO2 (2.75 to 39 wt%), as TiO2, Na2O and K2O decrease with increasing temperature. However, MgO shows little change at given pressures.
The project is a collaboration between Macquarie University (Sydney) and ANU RSES experimental group.