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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Geologic studies of the Pacific Ocean and its margins have advanced in the Soviet Union. Some of the results are presented on the unique published maps. (a) Tectonic Map of Eurasia, scale 1:5,000,000 (1966); (b) Geological Map of the Pacific Mobile Belt and the Pacific, scale 1:10,000,000 (1973); and (c) Tectonic Map of the Pacific Segment of the Earth, scale 1:10,000,000 (1970). Moreover, many maps and books have been published which deal with the geology and mineral resources of the northwestern segment of the Pacific including the eastern USSR.
A geologic map synthesizes the data on stratigraphy, age, and composition of sedimentary, volcanic, and intrusive rocks on the Pacific continental margins, in the island arcs, and on the Pacific Ocean floor. The arrangement of geologic complexes of different age and character reflects various styles of tectonic systems on the inner structure: ancient platform--perioceanic belt--ocean. A regular rejuvenation of geologic complexes from continental nuclei toward the ocean is indicated. The map also shows that the distribution of sediment types on the Pacific floor is determined by such factors as climatic zonation, position of zones of upwelling and subsidence of waters, and depth of the ocean; whereas, in the perioceanic zones, a tectonic factor influencing intensity of supply of terrig nous and volcanic material is especially important.
The tectonic map presents the structural formation of the Pacific area which is divided into four principal categories: folding zones of the ocean margins, recent geosynclinal zones, thalassogenes (large parts of the oceanic floor), and the East Pacific mobile belt. The structural analysis, on the whole, shows that plate tectonics fails to explain the constitution of the Pacific area. This hypothesis does not conform to the concept of the Circum-Pacific belt as the earth's structural zone of planetary importance. However, horizontal movements of rather large blocks and sheets of the Earth's crust are real.
The geologic-structural synthesis creates the basis for general metallogenic constructions. Further studies on concentric zonation in the arrangement of ore deposits around the Pacific Ocean appear promising. The zone adjacent to the ocean is rich in gold and copper; the next continentward zone is characterized by rich deposits of tin and tungsten (in addition to gold) in Asia, and lead and zinc in North America. The ophiolitic belts are characterized by peculiar complexes of metals. Study of morphologic and geodynamic properties of ore-controlling faults poses a special problem.
The ocean floor is characterized by extensive accumulations of manganese-polymetallic ores and locally by metasomatic phosphorites.
The geologic-structural synthesis is important for prediction of oil and gas prospects. About 140 actual and possible gas and oil basins have been recorded in the Pacific margins. Most of them are associated with depressions and basins within folded zones and oceanic depressions. The basins in the perioceanic sector are composed mostly of Cenozoic deposits; the main productive strata are Miocene to Pliocene in age. Oil and gas already have been detected in about half of the basins.
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