ACCRETION AND COLLISION OROGENIC BELTS OF NORTH-WESTERN SEGMENT OF PACIFIC

Two different types of fold and orogenic structures occur: Pacific and Mediterraniean, Cordilleranean and Alpine; Perioceanic and intracontinental; accretion and collision. Accretion type of fold belts is formed during the process of relationship of structures in transition zone continent-ocean, and collision type - during the collision of continent-continent. Pacific tectonic belt records accretion orogens as well as collision orogens. Their structure features are being studied on the example of collision fold belts: Verkhoyansk-Kolyma orogen (Yakutia), Brooks range (Alaska), South-Aniyuy suture (Chukotka) and accretion type - Koryak highland, Cordillera of Northern America.

Structure of Verkhoyansk-Chukotka Mesozoic orogenic area is formed as a result of collision of continent-microcontinent, continent - island arc. At the same time accretion structures and deformation type typical for them are originated (Oxman, 2001; Sokolov, Bondarenko et. al., 2001). Accretion complexes are also known in other folded structures of collision type (Moores, Twiss,1995; Sengor, Natal'in, 1996)

Koryak-Kamchatka Mesozoic-Cenozoic orogenic area represents typical example of continental margins of accretion type, during the amalgamation of terranes of different age and geodynamic type to the continent from the ocean (Sokolov, 1992: Nokleberg, Parfenov, Monger, et al. 1994; Bogdanov, Tilman, 1992). However, structures formed by collision processes are well shown here too. (Konstantinovskaya, 2001; Kovalenko, 2001).

The same processes act in forming fold belts, but structure can be expressed differently, that is determined by: scale of accretion and collision occurrences; types of collision (continent-continent, continent-arc etc.) and accretion; geological history; features of plates relationship (orthogonal or oblique subduction, age of oceanic crust, angle of dip of subduction zone etc.).

Consequently, when we talk about collision type of fold belts we mean prevailing role of collision, when we talk about accretion type of fold structures - we mean prevailing role of accretion structures and processes.

This work was supported by RFBR (grants 00-05-65105, 01-06-64535, 02-05-64217), RFBR-Arctic FCP "Integracia" (grant 0382) and "Universities of Russia" project (UR-09-01-033)