NEW METHOD FOR DETERMINING PRIMITIVE MELTS - EXAMPLE OF MELT INCLUSIONS IN SPINEL FROM THOLEIITES OF THE FAMOUS AREA, MID-ATLANTIC RIDGE

A new petrological method for determining primitive melts involves the examination of melt inclusions in spinel using microthermometric expe riments and microprobe analysis. Studies of quench glasses, phenocryst s, and melt inclusions in spinel of tholeiites from the FAMOUS area, M id-Atlantic Ridge, enables the compositions of the primitive liquidus association and the crystallization temperatures of the melts to be de termined. It is concluded that melt compositions can be determined usi ng the chemistries of the equilibrium olivine and spinel. It is demons trated that the primary melts of the rocks are not picritic, and they show variable contents of the most incompatible elements.