ROLE OF ISLAND ARCS IN THE DEVELOPMENT OF THE EARTH'S STRUCTURE

Convincing geological data show that oceanic structure of the earth's crust is secondary and formed as the result of destruction and basification of the continental crust. This process goes on under conditions of tension, of deep fault formation, and of strong basaltic volcanism.

Analysis of the structure and history of development of island arcs gives evidence enough to distinguish two types. Island arcs of the first type represent arching folded ranges, similar to continental folded arcs. They were formed in geosynclines, but in the process of basification the supporting interior massifs subsides, while the arcs themselves are preserved in the form of curved bands of the continental crust within the oceanized areas (Japan, Indonesia, the Antilles). During a process involving tension of the earth's crust these weakened geosynclinal zones became areas of large fracture formation initiating intensive volcanism.

Arcs belonging to the second type are not related to the previous geosynclinal development. They were formed as a direct result of tension of the earth's crust, in the environment of ocean development. The tension produced deep faults, and the curving of the trajectories of the tensional stresses in the process of fault growth gave rise to the arching of these faults. Being younger, arcs of the second type cross those of the first type.

The asymmetry of the Pacific Ocean is characterized by the fact that on the east the ocean is bordered by the Cordilleras and the Andes, forming a single weak zone, while on the western periphery of the ocean the crust resembles a mosaic with very heterogeneous structure.

Basification of the earth's crust and formation of oceans is the last known stage in the development of the earth, caused by radioactive heating of the earth's interior and subsequent smelting to tilt: surface of the deep material of the mantle. — author's English summary