Contributions to Mineralogy and Petrology

, Volume 74, Issue 1, pp 7-12

First online:

Melt density and the average composition of basalt

  • Edward StolperAffiliated withDivision of Geological and Planetary Sciences, California Institute of Technology
  • , David WalkerAffiliated withDepartment of Geological Sciences, Harvard UniversityLunar and Planetary Institute

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Densities of residual liquids produced by low pressure fractionation of olivine-rich melts pass through a minimum when pyroxene and plagioclase joint the crystallization sequence. The observation that erupted basalt compositions cluster around the degree of fractionation from picritic liquids corresponding to the density minimum in the liquid line of descent may thus suggest that the earth's crust imposes a density filter on the liquids that pass through it, favoring the eruption of the light liquids at the density minimum over the eruption of denser more fractionated and less fractionated liquids.