COMPOSITION AND FORMATION CONDITIONS OF INCLUSIONS IN THE MINERALS OFANDESITES FROM CENTRAL SLOVAKIA

Melt inclusions with high-density (>1 g/cm(3)) aqueous fluids were fou nd in andesite minerals (Solovova et at, 1992). Conditions of magma ge neration and crystallization were determined from data on the composit ions of glass and minerals from the inclusions. Initial melt was enric hed in aluminum, potassium, and chlorine and contained no more than 2 wt % of water. The occurrence of resorbed amphibolite xenoliths in the rock minerals suggests a contribution of this rock in the formation o f andesite melt under crustal conditions, Shallow-level ma,ama differe ntiation at 1100-1000 degrees C, accompanied by crustal contamination, resulted in the formation of a wide spectrum of silicic melts with up to 76 wt % SiO2. Possible scenarios are discussed for the formation o f melt inclusions with high-density fluids in plagioclase. The entrapm ent of these inclusions during plagioclase crystallization from magma is demonstrated to contradict the available experimental data on cryst allization in the system silicic melt-water. We propose that later reb illing processes were responsible for the formation of this fluid phas e.