| Abstract |
Data on a caldera discovered in 2006 are reported. The caldera formed in southern Kamchatka during Eopleistocene time (1.2 to 1.5 Ma). The caldera boundaries have been reconstructed and its dimensions determined (approximately 15-25 km). The area of study contains several groups of thermal springs: the Bol’she-Bannaya, Mal. Bannaya, Karymchina, Karymshina, and Verkhne-Paratunka ones. The largest are the Bol’she-Bannaya springs; these were investigated extensively by many different methods during the 1970s. The reconstruction of the boundary to the large caldera that exists in the area (Leonov, Rogozin, 2007) yields a different setting of the present-day hydrothermal systems, in particular, of the Bol’she-Bannaya system. The caldera boundary has been found to pass through the Bol’she-Bannaya springs area. It was also found that numerous emplacements of acid lavas (domes, dikes, short lava flows) occur at the boundary throughout its length, these formations being rather young, less than 0.5–0.8 Ma. These data suggest that the present-day hydrothermal activity in the area is related, on the one hand, to increased crustal permeability at the caldera boundary (due to the faults that exist there), while on the other hand, the large magma chamber existing in the area (above which the caldera was generated in the Eopleistocene followed by a resurgent dome in the Lower/Middle Pleistocene) retains its heat and continues to supply it to the fluids and water that are circulating around it. |