The Significance of Primary Scapolite in Granulitic Inclusions from Deep-seated Pipes

Sulphur-rich scapolite is described as a primary constituentof several granulite inclusions occurring, along with eclogiticand rare ultrabasic rocks, in the breccia- and basalt-filledpipes of eastern Australia. The wide distribution of such inclusionsin space and time indicates that granulites, some scapolite-bearing,form an important part of the base of the crust of this region. Two inclusions with the assemblage orthopyroxene-clinopyroxene-plagioclase-scapolite,two with the assemblage clinopyroxene-garnet-plagioclase-scapolite,and one with the assemblage orthopyroxene-clinopyroxene-plagioclase,have been analysed and chemical and optical data on the constituentminerals are given. Since it is impossible to adequately separatescapolite from primary and secondary plagioclase, partial analysesof these minerals have been made with an A.R.L. electron probeX-ray microanalyser. From our data and that obtained from the literature, we suggestthat scapolites with more than 10 mol per cent sulphur in theanion group are confined to rocks of the granulite meta-morphicfacies. Within the granulite facies there appears to be a progressiveincrease in the sulphur content of scapolite in equilibriumwith such sulphur-rich minerals as pyrrhotite, with increasingmetamorphic grade.