New data on age, material composition and geological structure of the Central Kamchatka depression (CKD). Part 1. Rocks types. Age, petrological and isotopo-geochemical characteristicsн

The paper presents new age and isotope geochemical characteristics for plateau effusive rocks from the Central Kamchatka Depression (CKD) and Nikolka Volcano. We compared these data with the data on rocks from the Klyuchevskoy group of volcanoes and also Sheveluch, Kharchinsky, Zarechny, Nachikinsky, Bakening volcanoes and NEB-adakites from Pliocene shield volcano between the Ozernaya Kamchatka and Pravaya Kamchatka rivers. It is shown that the evolutionally advanced (often more alkaline) rock from Nachikinsky, Bakening, Nikolka volcanoes and the Pliocene shield volcanoe significantly differ in isotope-geochemical characteristics from the Klyuchevskoy group of volcanoes rocks. Exactly this type of rocks is characteristic for CKD as rift structure. The Klyuchevskoy group of volcanoes rock are not typomorphic for this structure and manifest the usual orogenic volcanism stage, typical for much larger area. Miocene plateau effusive rocks differ from rocks of this group only by slightly increased potassium alkalinity. The rift type rocks characteristic feature is not only their increased alkalinity, but also specific microcomponents ratios: Ti/V > 0.004, Nb/Y > 0.28, Dy/Yb > 2.00, La/Yb > 6.5, Sm/Yb > 2.4, Lu/Hf < 0.08. Along with isotopic characteristics, these ratios suggest the existence of the single deep asthenospheric mantle reservoir for initial melts. The Kurile-Kamchatka and Commander-Aleutian island-arc systems’ junction is marked by the increased fluid enrichment (Ce group of REE) of melts for rocks of certain volcanoes: Shiveluch, Kharchinsky, Zarechny.