LATE MIOCENE-PLIOCENE TRANSFORM MARGIN OF KAMCHATKA

Testing of the geochemical compositions of the Late Cenozoic volcanites of Kamchatka on new discriminant diagrams confirmed the idea of the existence of different geodynamic regimes at this time. It is shown that the Late Miocene (~6 Ma)-Pliocene volcanites of Eastern Kamchatka and the Central Kamchatka Depression, as well as the Late Pliocene (~3.5 Ma)-Holocene alkaline, calcareous-alkaline, and adakite volcanites of the central part of the Middle Ridge are similar to the volcanites of the transform margins of the Pacific type. At the same time, the Miocene–Holocene volcanites of Southern Kamchatka, the Miocene-Early Pliocene volcanites of the Middle Ridge, and the Pleistocene–Holocene volcanites of Eastern Kamchatka are similar to the volcanites of the convergent margins. In the central part of Kamchatka (from the coast to the Middle Ridge), at the end of the Miocene-Pliocene, during the collision of the Kronotsky terrane of the island arc and the slip of the Pacific plate, magmatic complexes typical of the transform margin were formed in this area. The geochemistry of the transform margin volcanites is due to the upwelling of the subslab asthenosphere both into the collision zone and into the zone of the volcanic arc of the Middle Ridge, after the rupture and subsequent separation of the Komandor-Kronotsky microplate slab.