Immiscibility in acidic magmas: Evidence from melt inclusions in quartz phenocrysts of ignimbrites
Naumov, Vladimir B.; Solovova, Irina P.; Kovalenker, Vladimir A.; Rusinov, Vladimir L.
European Journal of Mineralogy Volume 5 Number 5 (1993), p. 937 - 942
published: Jan 1, 1993
manuscript accepted: Apr 23, 1993
manuscript received: Jun 11, 1991
ArtNo. ESP147050505017, Price: 29.00 €
Abstract Unusual melt inclusions occur in quartz phenocrysts of the Lashkerek ignimbrites in the Kurama Mountains, Central Asia; the inclusions provide evidence of immiscibility in high-temperature acidic magmas, leading to the separation of iron-rich globules from the silicate melt. Inclusions contain gas (10-14 vol.%), translucent glass (85-90vol.%) and one (sometimes several) spherical or semispherical ore globules (0.4 to 1.0 vol.%). Average composition of the globules from microprobe analyses is (in wt.%): 81.2 FeO, 9.9SiO2, 2.2 A12O3, 0.36 K2O, 0.34Na2O, 0.27 CaO, 0.19 ZnO, 0.16 MnO, 0.01 TiO2, 0.01 Cl. E.M.Raster scan profiles of the characteristic radiations of Si, Fe and Al with a magnification of 8000 × reveal a homogeneous distribution of the elements in the globules. The siliceous glass matrix to the iron-rich globules contains (in wt.%): 70.2 SiO2, 17.7 Al2O3, 0.32 FeO, 0.66 CaO, 3.7Na2O, 6.7 K2O, 0.29 Cl. The ore globules dissolve in the siliceous melt at 1050-1100 °C, and total homogenization occurs at 1140-1250 °C.