FRAGMENTS OF SIALIC CRUST IN LATE CENOZOIC VOLCANICS IN THE SOUTHERN PART OF THE KORYAK MOUNTAINS

Abstract

Characteristic features of Late Cenozoic volcanics fringing the Komandor Basin, Bering Sea, are the lateral compositional inhomogeneity, expressed in their enrichment in high-charge lithophile and light rare-earth elements, and a change from dry melts to water-rich ones from the northern part of the volcanic belt in the Pakhacha Range toward the southern in the Vyvenka River basin and on the Kamchatka Isthmus. This inhomogeneity results from the heterogeneity of the lithosphere, which is suboceanic in the north and subcontinental in the south. Such an assumption is confirmed by our finds of xenoliths of rocks of the granulite metamorphic facies in andesite-basalt lavas of the Vyvenka River basin in the southern part of the Koryak mountains, USSR. The inclusions of rocks of the granulite facies probably represent the lower layers of this crust. Its upper part could have consisted of amphibolites and granitoid rocks, as in southwestern Japan. The latter have also been found as inclusions in Late Cenozoic lavas of the Vyvenka River basin and the Kamchatka Isthums.