Okorusu magnetites exhibit abundant exsolutions
of ulvospinel in a characteristic cloth texture, and oxidation exsolution
2]O saturation occurs by exsolution
of an aqueous fluid to forma distinct phase in the silicate melt, at which point the fluid boils and gas bubbles form.
The assemblage titanite-magnetite-quartz-pyrrhotite may be a late auto-oxidation and sulphidation product of vapour exsolution (Candela 1991), as it is not consistent with high Fe (-Ti) biotite (Wones 1981).
The fine-grained groundmass and minor granophyric (wormy) to more prevalent graphic (cuneiform) texture resulted from quench crystallization (low degrees of supercooling) of the dyke, possibly enhanced by vapour exsolution and depressurization (see Fenn 1986; Lentz and Fowler 1992).
There is no kinetic barrier to heterogeneous nucleation of bubbles; therefore, the exsolution surface (level in the chamber or conduit) is synonymous with the saturation surface because volatiles exsolve during magma ascent (Fig.
It is the expansion of the volatile phase following exsolution and magmatic fragmentation which produces the kinetic energy required to accelerate the magma-volatile mixture to the surface producing an explosive eruption.
The miscibility gap is narrower at high temperatures, so that under slow cooling conditions, early formed augites and low-Ca pyroxenes develop exsolution
lamellae as low-Ca pyroxene and augite (respectively) are expelled from the structures.