Processes of the formation of mugearitic and benmoreitic magmas on Nemrut Volcano (East Turkey)

Аннотация

The samples of trachybasalt, mugearite, benmoreite, trachydacite, and comendite from Nemrut Volcano (East Turkey) were studied. Except for trachybasalt, each sample contains partly dissolved mineral xenocrysts from magmas with different compositions. At the precaldera stage of volcanic evolution fractional crystallization of the alkali basaltic melt contaminated with a small amount of material of the upper crust, as well as mixing of trachybasaltic and trachydacitic magmas, could result in the formation of mugearitic magma. At the precaldera stage benmoreitic magma formed as a result of the evolution of trachybasaltic and mugearitic magmas, while at the postcaldera stage—after the mixing of trachybasaltic magma and low-Fe comenditic melt. The presence of relics of postcaldera benmoreitic magma in comendite (glass of trachyrhyodacite–trachyrhyolite composition, xenocrysts of Mg-rich olivine, plagioclase, and augite) allows us to assume that repeated eruptions at the postcaldera stage of volcanic evolution were caused by its eruptions into the low-Fe comenditic magma.