One-atmosphere density measurements at very high temperatures have been performed on four mantle melts in the FeO-Fe 2 O 3 -CaO-MgO-Al 2 O 3 -SiO 2 system (FeO-rich peridotite, PHN 1611, komatiite, and fayalite), using the Ir-based double-bob Archimedean method in air. The one-atmosphere density of the investigated materials ranges from 2.6 to 3.6 g/cm 3 from their respective melting points up to 2123 K. Combined with earlier high-pressure static experiments on the same compositions, the present one-atmosphere densities provide robust constraints on the isothermal compression curves of such Fe-bearing silicate melts and yield new values of the isothermal bulk modulus (K T ) and its pressure derivative (K′ T ) through application of the third order Birch-Murnaghan equation of state. The present K T and K′ T values are significantly different from those previously reported using the high-pressure dataset together with calculated one-atmosphere densities using existing schemes. Comparisons with K T - K′ T systematics from the literature are also made.
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