Silica-rich melts originating from melt-hydrated peridotite reactions

Abstract

Interactions between melts and hydrated peridotite may control production of silica-rich melts, fluids and magmas in the upper mantle and may be predominant mechanism for producing felsic crust in shallow ultramafic settings of rocky planets. This research investigated composition of olivine-hosted mineral, melt and multi-phase inclusions in dunite xenoliths from the 1800–1801 Kaupulehu flow of Hualalai Volcano. The host olivine (forsterite Fo 82–89 , mol. %) appears with mineral inclusions of crystalline chromite having compositions similar to those found in alkaline series rocks. Abundant silica-rich glasses (SiO 2 = 63 ± 2.9 wt%, Al 2 O 3 = 21 ± 1.2 wt%; K 2 O = 4.3 ± 0.5 wt%, Na 2 O = 3.6 ± 0.7 wt%, 38 analyses) found in the olivine-hosted melt and multiphase inclusions are interpreted as quenched silicate liquids entrapped due to nephelinite melt percolation in hydrated harzburgite in the presence of free aqueous fluid at pressures of 0.7 to 0.1 GPa and a melt-to-peridotite mass ratio of 0.2 to 0.3. This work also re-interprets the metasomatic origin of global examples of silica-rich glass inclusions in peridotite xenolith minerals according to results from recent experiments on melt-hydrated peridotite interaction processes. As a planetary process, production of silica-rich melts and fluids within series of associated magmas and their crystallized differentiates can occur due to reaction of primitive mafic (e.g., ocean island basalt, OIB) melts with hydrated peridotite (or serpentinite) in the presence of aqueous fluids at pressures below 1 GPa. • Si-rich glasses are produced due to reaction of mafic melts with hydrated peridotite.