Solidus and liquidus temperatures and mineralogies for anhydrous garnet-lherzolite to 15 GPa |
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| Authors: | Claude T Herzberg |
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| Institution: | Department of Geological Sciences, Rutgers University, New Brunswick, NJ 08903 U.S.A. |
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| Abstract: | A review of experimental data for systems, pertaining to anhydrous fertile garnet-lherzolite shows strong convergence in the liquidus and solidus temperatures for the range 6.5–15 GPa. These can converge either to a common temperature or to temperatures which differ by only ～ 100°C. The major-element composition of magmas generated by even minor degrees of partial melting may be similar to the primordial bulk silicate Earth composition in an upper-mantle stratigraphic column extending over 160 km in depth.The convergence of the solidus and liquidus temperatures is a consequence of the highly variable of the fusion curves for minerals which crystallize in peridotite systems. In particular, for the forsterite fusion curve is much less than that for diopside and garnet. Whether or not the solidus and liquidus intersect, the liquidus mineralogy for undepleted garnet-lherzolite compositions changes from olivine at low pressures to pyroxene, garnet, or a complex pyroxene-garnet solid solution at pressures in excess of 10–15 GPa. Geochemical data for the earliest Archean komatiites are consistent with an upper-mantle phase diagram having garnet as a liquidus phase for garnet-lherzolite compositions at high pressures. All estimates of the anhydrous solidus and liquidus for the range 10–15 GPa are consistent with silicate liquid compressibility data, which indicate that olivine may be neutrally buoyant in ultramafic magmas at these pressures. |
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