DEEP PLANETARY FAULTS IN THE EARTH'S CRUST Many books and articles have been written about the structure of the Earth's crust, but it is only recently that geophysical observations have made it possible to specify the basic subsurface features of this structure. The Earth's crust, which has a thickness varying from 5 to 75 km, is characterized by physical parameters which are quite different from those of the underlying intermediate layer, the outer parts of which are known as the upper mantle. An intensive exchange of matter and energy takes place between the mantle and the overlying Earth's crust, and the mantle constitutes a source of the movements and development of the crust. Different portions of the crust react in different ways to the influence of the upper mantle, and as a result the Earth's crust is now made up of large blocks, differing from one another in structure and divided from one another by deep faults. Each of these blocks has its own characteristic depth cross section, with some combination of basaltic, granitic, and sedimentary layers. Moreover, each block has its own characteristic geological system of surface layers, its own particular type of geological structural forms, and its own evolutionary history. A block is usually framed by deep faults in the crust, and is often even cut up by such breaks and faults.
Some typical indications of deep faults are: 1) a pronounced difference between the deep structure of the crust on the two sides of a fault; 2) intensive uplift of the heavy, deep magmas along faults; 3) the appear ance of sharp gravitational and geomagnetic anomalies over faults; and 4) the formation of rich, sizable mineral deposits in the fault zones. It is interesting that, according to all these criteria, a formation in the Earth's crust such as the Urals should be considered as a deep fault. The Precambrian Russian Platform extends to the west of the Urals, and as early as the first part of the Paleozoic era sedimentary layers were gently deposited on it. To the east of the Urals, however, the intensive impregnation of the Earth's crust with deep magma only stopped prior to the Jurassic period, at which time the rigid Paleozoic fundament was able to become consolidated. In the Urals the deep greenstones rose up
to the Earth's surface, and heavy-dunite massifs of basic composition were formed. The Urals are characterized by marked gravitational and magnetic anomalies. And finally, in the depths of the Urals, innumerable, really fabulous, resources of precious stones were stored up.
The Urals represent a deep fault of ancient origin. There are, however, some deep faults in the world which are more recent. Let us consider the transition zone from the Pacific Ocean to the Asian continent, which was recently studied by Soviet scientists during the International Geophysical Year (1957-1958) /6/. The deep fault in the planet's surface located in this zone is known as the Kuril Island Arc. West of this arc the Earth's crust has an overall thickness of 30 to 35 km and is definitely of the continental type, while to the east it narrows down to 5 to 8 km and is oceanic. Even at present, along the Kuril-Kamchatka volcanic line products of deep-magma differentiation are brought up to the surface, and the depths of the region are shaken by powerful seismic jolts. The Kuril Kamchatka tectonic line on the Earth's surface is associated with strong anomalies of gravity and of the magnetic field.
Another deep fault, part of which extends under the ocean, was studied by the Dutch geophysicist Vening Meinesz /7/. This fault is the Indonesian island arc, together with its submarine framework. The Soviet geophysicist Lyustikh has shown very graphically that those oceanic zones which were described by Vening Meinesz as downfoldings of the crust are actually junctions between two different types of crustal blocks /8/. Vening Meinesz, Kuenen, and other investigators after them suspected that in the submarine region of the Indonesian arc we are dealing with the rudiments of a mountain chain on the Earth's crust, and the more explicit treatment of Lyustikh serves to bolster this idea.