The East Asian system of volcanic belts is situated between the area of Cenozoic folding in the northeast Circum-Pacific region and more ancient, mainly Mesozoic tectonic zones. The extent of the East Asian volcanic system is comparable to that of recent volcanic arcs.

The largest element of the East Asian system, the Okhotsk volcanic belt, contains structures characteristic of those of the marginal volcanic belts. The basic features of the belt were formed during the Aptian-Albian and Cenomanian-Turonian. During that time period, andesite volcanism prevailed, although granitoid magmatism was widespread and was accompanied by the formation of ignimbrite fields of large volume.

Comparative structural, petrologic, and historic-geologic analyses have revealed considerable differences between the Okhotsk-Chukotsk belt and the Kuril-Kamchatka volcanic arc.

A specific zone of intensive uplift and subaerial, mainly andesite volcanism was stabilized in the structures of the basement of the Okhotsk-Chukotsk belt. Formation of this zone was simultaneous with the deep-seated faulting which separated the Verkhoyansk-Chukotsk and the Koryak-Kamchatka geosynclinal regions in the Mesozoic. During the Late Jurassic and the first half of the Early Cretaceous, the Okhotsk-Chukotsk volcanic zone (in relation to the mentioned regions) had the same function as does the Kuril-Kamchatka volcanic arc today in relation to Kamchatka, the Okhotsk Sea, and Hokkaido, on one side, and the Kuril-Kamchatka trench on the other.

The presumably Late Jurassic-Early Cretaceous volcanic arc was a peculiar bordering structure which separated the Anadyr'-Koryak geosynclinal system (in an early stage of its development) from the Verkhoyansk-Chukotsk region of Mesozoic folding (in the epigeosynclinal stage of orogenesis). Development of the Okhotsk-Chukotsk marginal volcanic belt began in Aptian-Albian time--when a considerable volume of terrigenous sediment was accumulating in the Anadyr'-Koryak geosynclinal system, and the Verkhoyansk-Chukotsk area represented part of a continental block with a tendency to rise. The volcanic belt included not only the volcanic arc, but also extended far beyond--over Mesozoic fold structures, ancient rigid massifs, and the peripheral zone of the Anadyr'-Koryak geosynclinal system. >

Gradual migration of volcanic arcs toward the Pacific did not occur in Northeast Asia. Their appearance and development in space and time bore an uneven character. The development and the nature of the mentioned structures are important tectonic aspects of the general problem of andesite volcanism.