QUANTIFYING THE ROLE OF FLUID AS RELATED TO MELT MOVEMENT IN THE CHAOTIC ZONE OF THE THERMAL AUREOLE IN THE BALLACHULISH IGNEOUS COMPLEX, SCOTLAND
The equilibrium assemblage observed outside the Chaotic Zone suggest metamorphic conditions of 550 to 635°C in the presence of 0.4-4.3 mol % water. Petrography and modeling of mesosome compositions yield temperatures of 550-622°C and water abundances of 0.6 to 5.3 mol % for the stable mineral assemblage Qz + Kfs + Pl + Ms + Rt + Sil + Opq ± And. Based on measured water abundances defined by LOI, water binaries predict that water was present as stoichiometric rather than free water, and likely accommodated by muscovite. The observed partial melt assemblage yield model temperatures of >635°C, defined by the mineral assemblage Qz + Kfs + Pl + Sil + Crd + Opq. Modeling of partial melt volumes suggest that temperatures in the sample would need to reach temperatures in excess of 900°C to produce the observed volume of partial melt. This suggests that the observed volume of melt reflects melt accumulation in the sample rather than in situ melting. Modeling and petrography of the samples suggests that melting reactions on the Western flank of the Ballachulish Igneous Complex may not have required the addition of excess water from the pluton, but melt migration may have altered effective bulk composition.