The Structure of the Discharge Site of Steam Hydrothermal Fluids in the Area of the Upper Pauzhetka Thermal Field (Southern Kamchatka)

Abstract

Abstract —Comprehensive geological and geophysical investigations were conducted to obtain new data on the structure and physical nature of the discharge site of steam hydrothermal fluids by the example of the Pauzhetka geothermal deposit (southern Kamchatka). An isometric concentric zonal structure has been identified within the temperature, geoelectric, magnetic, and gravimetric fields. It spatially correlates with an elevated tectonic block previously detected in the area of the Upper Pauzhetka thermal field. The central part of this structure includes a consolidated rock block composed presumably of quartz–adularia metasomatites formed at the pre-Holocene stage of evolution of the Pauzhetka hydrothermal system. The rocks form a physical heterogeneity within the structure of the aquifer, which greatly contributes to the distribution of flows of ascending thermal, mixed, and meteoric waters beneath the Upper Pauzhetka thermal field. The central area of the isometric concentric zonal structure is outlined by a zone consisting of local anomalies of positive magnetic-field values. The wide occurrence of subintrusive bodies (sills, dikes, and extrusion roots) of intermediate to rhyolite composition suggests the magmatic nature of the identified anomalies. The peripheral areas correlate with large discharge sites of high-temperature fluids. Thus, it is demonstrated that the structure of the circulation zones of waters of various types in the area of the Upper Pauzhetka thermal field is governed by the concentric zonal structure of the elevated tectonic block and the distribution of physical heterogeneities, both primary (of magmatic or volcanosedimentary nature) and resulted from the hydrothermal metasomatic alteration of the source rocks.