Multiphase Mineral Inclusions in Ferrikaersutite Megacrysts : Implications for Postmagmatic Alteration of the Kaersutite Host

Abstract

Primary and secondary multiphase mineral inclusions, without preserved fluid are found in ferrikaersutite megacrysts from the Cenozoic Harrat Ash Sham Volcanic Field in ٍSyria. Mineral phases in the inclusions are magnetite, hematite, pseudobrookite and pyrrhotite. The kaersutite megacrysts formed from a hydrous basanitic melt at depth. Silicate minerals in the inclusions are olivine, plagioclase, phlogopite, hornblende, clino- and orthopyroxene. These silicate minerals crystallized from melt penetration and infillings of veins and fractures in the kaersutite. Magnetite and pyrrhotite inclusion formed through magmatic crystallization which was followed by low temperature alteration and re-equilibration. Late stage near-surface alteration resulted in the formation of hematite, limonite and fine-grained weathering products which comprise high-Fe-Si-, Si-Mg-Al-, Si-Fe-Al-, Si-Al- and Si-Ti-Al-Fe-Ca-rich alterations. The composition of these late stage alteration products was governed by low-temperature post-magmatic alteration of kaersutite along cleavage planes and fractures.