Late Cretaceous-Paleocene Magmatic Complexes of Central Kamchatka: Geological Settings and Compositional Features

摘要

A comparative analysis of the Late Cretaceous–Paleocene volcanism was conducted for four areasof Kamchatka: the Pravyi Tolbachik–Levaya Shchapina–Adrianovka interlfuve (the northern part of the Tum-rok Range), the area south of the Ipuin River and Mt. Khrebtovaya (the northern Valaginsky Range), the areaof Mt. Savul'ch (the upper reaches of the Kitil'gina River, northern Valaginsky Range), and the Kirganik-Levaya Kolpakova interfluve (the Sredinny Range). New petrochemical, geochemical, and isotopic data on thevolcanic rocks from these areas are reported. The examination of this material, together with already publisheddata on volcanic and plutonic rocks of similar composition and age, made it possible to establish the following:(1) the considered basaltoids are ascribed to the subalkali basalt–trachyandesite series with transition toward ameymechite–picrite rock association; (2) the alkali content in the rocks of the Valaginsky–Tumrok–Sredinnyranges increases simultaneously with the increase of the Rb content, while the contents of HFSE and radioactiveelements decrease and then again increase. Two trends are identified in the Yb_n–Ce_ndiagram: a positive trendspanning most of the volcanic and plutonic rocks and a negative trend defined by the data points of the meyme-chite–picrite association. The first trend reflects the rock evolution during crystallization differentiation, whilethe second trend was produced by different degrees of melting of initial protolith. The possible geodynamicreconstructions of this volcanism are discussed as well.