Abstract:
The Uzon caldera is a genetically complex structure, which was formed during several episodes of tectono-magmatic activity. It is made up of basalts, basaltic andesites, and dacites, the products of the normal evolution of tholeiitic magma, which were reworked considerable by a magmatic-hydrothermal process. New data are presented on the petrography and geochemistry of the basalts and dacites. Variations of δ18O and 87Sr/86Sr are described, and the role of the contamination of these elements in the hydrothermal process is discussed. It was found that the hydrothermal alteration of the silicic rocks had resulted in the cardinal transformation of their chemical composition. Some of their petrogenic elements were removed and involved, along with secondary minerals, into the caldera-lake sedimentation and lithogenesis.