The effects of mantle composition on the peridotite solidus: Implications for the magmatic history of Mars

At a given pressure, terrestrial peridotites of varying composition may have solidus temperatures that differ by up to 100 °C. Based on meteorite evidence, the mantle of Mars is believed to be enriched in Na and K and to have a higher Fe/Mg ratio (lower magnesium number, Mg#) than Earth. These differences all favor a mantle solidus temperature on Mars that is lower than on Earth and are important in understanding the volcanic history of Mars. We parameterize the peridotite solidus at 1 and 3 GPa as a function of Mg# and total alkali content, using existing measurements of peridotite melting at 1 and 3 GPa for Mg# between 75 and 91 and total alkali content between 0.06 and 1.17 weight percent. The solidus on early Mars was likely 30-40 °C lower than on Earth, which increases the predicted crustal production by about 20% over martian history, relative to a Mars model that uses a solidus calculated for terrestrial peridotite composition. Because Na is incompatible and migrates to the crust over time, the present-day martian solidus is higher than the primitive solidus but is still ∼15 °C less than on Earth. This enhances the present-day magma production rate at martian mantle plumes by a factor of 2-3.