Pacific Geosynclinal Belt

Pacific Geosynclinal Belt

 

the world’s largest geosynclinal belt, comprising folded structures of various ages and modern geosynclinal zones of the earth’s crust rimming the Pacific Ocean. The Pacific geosynclinal belt is divided into the Eastern Pacific (Cordillera) geosynclinal belt and the Western Pacific geosynclinal belt.

The belt is separated from the ocean floor by deep-sea trenches, of which the largest are the Aleutian, Kuril-Kamchatka, Marianas, Tonga, Kermadec, Peru, Chile, and Guatemala trenches. Its outer boundary is formed by the edges of ancient continental platforms—the Siberian, Sino-Korean, South China, Australian, Antarctic, South American and North American. Along its outer ring the belt extends for some 56,000 km, and its width ranges from a few hundred kilometers to 3,000–5,000 km.

Within the Pacific geosynclinal belt two structurally diverse parts have been established, a rear and a frontal part. The former, a continental structure of the earth’s crust, is composed of geosynclinal folded structures of the Late Precambrian (Australia), the Paleozoic (southeast China and eastern Australia), the Mesozoic (the Verkhoiano-Chukotka region, Sikhote-Alin’, and the Cordilleras of North America), and the Cenozoic (the Andes and Antarctica). The latter, directly adjoining the ocean floor, consists of structural zones on which a continental crust has not yet formed. They include the island arcs, the deep-sea trenches, most of the marginal seas, and the large islands and continental margins that have been affected by Late Cenozoic folding (Sakhalin, Taiwan, northern Kalimantan and New Guinea, California, southern Alaska). The closer to the ocean floor, the younger the tectonic zones; correspondingly, the continental areas increase. However, because of the belt’s high tectonic mobility, this process is a complex one, accompanied by the destruction and displacements of tectonic structures in different directions, as well as by changes in the plutonic structure of the earth’s crust.

Within the Pacific geosynclinal belt lies the earth’s “ring of fire,” a ring of young volcanoes whose eruption products consist chiefly of andesite. Also associated with the ring of fire are strong seismic processes, including earthquakes whose epicenters lie at depths of up to 700 km. The belt also has a markedly higher concentration of mineral deposits than adjacent areas of the earth’s crust. The continental parts of the belt contain deposits of gold, silver, tin, tungsten, and complex ores; in the littoral areas are found ores of copper, iron, chromite, nickel, platinum, and gold. Mercury deposits occur in the volcanic zones.

Large deposits of oil and gas are associated with the belt. One group of such deposits is located along the boundaries of the belt, at its junction with the ancient platforms (Verkhoiansk trough, troughs of North and South America). Another group is associated with the deep troughs filled with Late Cenozoic deposits (Sakhalin, California, Kalimantan). Large deposits of oil and gas also lie beneath the waters of the marginal seas.

REFERENCES

Pushcharovskii, Iu. M. Vvedenie v tektoniku Tikhookeanskogo segmenta Zemli. Moscow, 1972.
Obshchie i regional’nye problemy tektoniki Tikhookeanskogo poiasa. Magadan, 1974.

IU. M. PUSHCHAROVSKII

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