© A.P. Sedov 1, V.V. Matveenkov 1, L. P. Volokitina 1, V.A. Rashidov 2,
G.I. Kazakevich 2, S. V. Lukyanov 2

1 Institute of Oceanology RAS. Moscow, 117997
2 Institute of Volcanology and Seismology, FED RAS, 683006 Petropavlovsk- Kamchatsky, Piip Blvd., 9,
e-mail: rashidva@kscnet.ru.

At present the opinion has dominated that intraplate volcanism in ocean is connected with hotspot activity. However, there exist the seamount chains, in which the age of magmatism in no way confines in theory of the lithospheric plates motion over a fixed thermal plumes in the asthenosphere. The Magellan seamount chain in West Pacific Seamounts Province (WPSP) is structure of this type. The age of volcanism in WPSP changes from 120 m.y up to 80 m.y. and ancient mountains are situated in the beginning and the end of the chain, but younger ones are located in its central part. Paleoreconstructions show that seamounts of the WPSP have been is formed in the vicinity of 20° S. Processes of volcanism were terminated here when this part of the plate approached to equator. Exactly on 20° S, under moving of lithospheric plate on the surfaces of geoid northward, the maximum curvature occurs in the lithosphere. In this region South Pacific Isotopic and Thermal Anomaly (SOPITA) is located. Within this anomaly at present volcanic island chains of French Polynesia are formed, and modern volcanoes are in the neighbourhood of seamounts with age of 40-45 m.y. The age analysis of French Polynesia volcanic chains shows that they also do not agree with theory of hotspots. Our estimates of rigidity of the lithosphere show that described volcanic structures could be formed on deep fractures appeared in lithosphere, under its motion through SOPITA. Such approach explains well all age and structural particularities both seamounts of WPSP, and volcanic islands of French Polynesia.