STRUCTURE AND RADIOMETRIC AGE OF A MIOCENE ANDESITE FORMATION IN SOUTHERN KAMCHATKA

Abstract

The Miocene andesite formation of southern Kamchatka consists of the Stenovaya, Yuzhno-Bystraya, Akhomteni, Zavoikovo, and Yushino volcano-plutonic rock associations. Each of these associations consists of a volcanic and a hypabyssal complex of the same name, which were identified on the basis of petrographic, stratigraphic, and structural evidence. Most of the complexes are characterized by radiometric, usually K-Ar ages. The 36 K-Ar ages presented in this paper indicate that the volcanic rocks were emplaced mainly during a period of 14-18 million years (early Miocene to the beginning of middle Miocene). The hypabyssal rocks were intruded mainly in a period of 11-15 million years, during the middle Miocene, mostly at the middle-late Miocene boundary.