Okhotsk-Chukotskiy Belt and Problem of Volcanic Arcs in Northeast Asia: ABSTRACT

Abstract

1. The East Asian volcanic belt system is between the circum-Pacific zone of Cenozoic folding in the northeast and the interior, more ancient, mainly Mesozoic tectonic zones. The size of the East Asian system is comparable to that of recent volcanic arc systems. 2. The largest element of the East Asian system, the Okhotsk volcanic belt, is characteristic of marginal-volcanic belt structures. The basic features of the belt were formed during the Aptian-Albian and Cenomanian-Turonian Stages. Andesite volcanism prevailed during these stages. In addition, granitoid magmatism was widespread and accompanied by the formation of large-volume ignimbrite fields. 3. Comparative structural, petrologic, and historic-geologic analyses reveal a considerable difference between the Okhotsk-Chukotskiy belt, on the west, and the Kuriles-Kamchatka arc, on the east. 4. Subaerial, mainly andesitic volcanism formed a well-defined zone--now widely exposed--in the basement structures of the Okhotsk-Chukotskiy belt. The zone developed simultaneously with a system of deep faults, which during the Mesozoic separated the Verkhoyansk-Chukotskiy belt (west of the Okhotsk-Chukotskiy belt) and the Anadyr-Koryak-Kamchatka geosyncline (east of the Okhotsk-Chukotskiy belt). During the Late Jurassic and the first half of the Early Cretaceous, the Okhotsk-Chukotskiy volcanic belt (in relation to other belts mentioned) played the same role as does the Kuriles-Kamchatka volcanic arc today. The Kuriles-Kamchatka arc separates western Kamchatka, the Sea of Okhotsk, and Hokkaido on one side from the Kuriles-Kamchatka Trench on the other. 5. The Late Jurassic and Early Cretaceous Okhotsk-Chukotskiy volcanic arc was a peculiar bordering structure, which separated the Anadyr-Koryak-Kamchatka geosyncline system (a trench on the east), then at the early stage of its development, from the Verkhoyansk-Chukotskiy region of Mesozoides which was in a more advanced stage of development (stage of epigeosyncline orogenesis). Development of the Okhotsk-Chukotskiy marginal volcanic belt began during the Aptian-Albian when the Anadyr-Koryak-Kamchatka system entered a stage when there was a large terrigeneous sedimentary accumulation, whereas the Verkhoyansk-Chukotskiy area was a consolidated continental block tending to rise. The volcanic belt developed on the site of the volcanic arc and extended far beyond the limits of the original arc--covering Mesozoides structures, even older massifs, and the peripheral zone of the Anadyr-Koryak-Kamchatka geosyncline system. 6. Gradual migration of volcanic arcs toward the Pacific did not occur in northeast Asia. Instead, the appearance and development of northeast Asian arcs were somewhat irregular in time and space. The structure and tectonic development of these belts and structures are important in considerations of the general problem of andesite volcanism. End_of_Article - Last_Page 2468------------