IDENTIFICATION AND FORMATION OF FELSIC ROCKS ON MARS

Felsic rocks dominate Earth’s upper continental crust and the ancient lunar highlands. They have not been broadly identified on Mars, which lacks plate tectonics and may have been too active geologically to retain widespread surface evidence for an early magma ocean. Here we report near-infrared spectral evidence for felsic rocks in isolated locations across Mars. These rocks are spectrally consistent with anorthosite but could also contain quartz; some are accompanied by hydrated secondary phases. One occurrence in the Nili Patera caldera is spatially associated with hydrated silica and a dacitic flow. Thermodynamic phase equilibria calculations show that fractional crystallization of anhydrous dacitic magma can yield felsic residual melts consistent with our observations. Felsic rocks imply significant magma evolution on Mars, and provide an alternative pathway besides intensive weathering to form materials enriched in secondary aluminosilicates.