Ascent of felsic magmas and formation of rapakivi

The wide compositional range of rapakivi-bearing rocks strongly suggests that process, not composition, governs the formation of rapakivi texture. A computational investigation was undertaken to determine whether decompression can induce the formation of the common features of rapakivi. Crystallization path calculations were conducted for seven rapakivi-bearing magma compositions at pressures in the range of 1-8 kbar to determine the effect of decompression on the phase stabilities of plagioclase, quartz, and alkali feldspar. These calculations indicate that decompression can produce parageneses that can lead to all of the characteristic features of rapakivi under certain conditions. -from Author