17 - Early Mesozoic magmatism in the Russian Far East

Summary

Tectonic activization of the East Asia regions in Triassic and early Jurassic times, when the Pacific Plate began to move to the north, resulted in the crushing of the continental plate into individual blocks, with cores of ancient massifs separated by sutures and faults. Movements along those faults were accompanied by magmatic processes.

In rift troughs, which developed in ancient massifs or along their margins, lavas of basic composition erupted. Those kinds of structures include the Bikin Trough and some small rifts in northern Sikhote-Alin, the Omolon Rift on the Omolon Massif, the Zyryanovsk Graben on the margin of the Kolyma-Omolon block, and the Verkhoyansk fold system, developed on the submerged part of the Siberian Platform.

Rifts and troughs in those areas occur along the zones where the plate and geoblock join and are related to regional faults. They are filled with sedimentary-volcanogenic complexes, in which basic volcanic rocks are represented mainly by alkaline basaltoids, differentiated alkaline gabbro massifs, and tholeiitic basalts.

In the collision zones along the continental margin, island-arc systems were formed. Two groups of island-arc belts can be distinguished: interblock island arcs within the crushed Asian continent and a system of island arcs along its margin. The first group includes the Alazeisk Arc, of latitudinal direction, located between the blocks of the Omolon and Chukotka massifs along the South Anyui Suture.