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Advances in research of Asian geology¡ªA summary of 1:5M International Geological Map of Asia project
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文摘
The International Geological Map of Asia at a 1:5,000,000 scale (IGMA5000) is the first digital Asian geological map under the standard of the Commission for the Geological Map of the World (CGMW). Major advances that have been achieved in compiling the map are manifested in the following understandings.

(1)

Large amounts of Mesozoic volcanic rocks occurring in the eastern Asian coastal area are mainly Cretaceous instead of Upper Jurassic-Lower Cretaceous. Most of the Carboniferous-Permian volcanic rocks in Central Asia seem not to be arc volcanics, but the product of an extensional stage. The basal boundary of the Meso-Neoproterozoic Jixian section in China is not dated at 1.8 Ga as defined previously, but less than 1.68 Ga.

(2)

The most significant Neoarchean tectono-thermal events in the Sino-Korean craton and the Indian craton took place at 2.5 Ga rather than at 2.7 Ga. The basement of the Yangtze craton was finally formed at 0.75-0.8 Ga, which is 0.2-0.3 Ga later than the Greenville orogenic cycle. Geologically, South China is identified to be an Early Paleozoic Caledonian foldbelt. The Qinling belt, where no oceanic basin was developed in Triassic times, is not an Indosinian collisional orogen, but a continental crust subduction one. When Pangea was formed, Indo-Australian Gondwana had been joined to Paleo-Asia and between them there was no oceanic basin, i.e. no Paleo-Tethys which continued from Paleozoic to Mesozoic. A huge Indosinian orogenic belt existed on the southern margin of Paleo-Asia to the north of the Zagros-Himalayas.

(3)

Asia is a composite continent consisting of three major cratons¡ªthe Siberian, Indian and Arabian and three huge orogenic belts with a number of minor cratons and numerous microcontinents included. The main body of the Asian continent took its shape during the Mesozoic. The orogenic belts belong respectively to three global tectonic domains: the Paleo-Asian, Tethyan and Pacific. The small cratons, such as Sino-Korea, Yangtze, Tarim, and Sibumasu are thought to be affiliated to the tectonic transform zone between Gondwana and Siberia. They had been situated on the northern margin of Gondwana before the disappearance of the Paleo-Asian Ocean, and were lying on the southern margin of Paleo-Asia after the closing of the Paleo-Asian Ocean and then the opening of the Tethys. The fact that ophiolites in Asia appear to get progressively younger in age from north to south throws light on the Phanerozoic evolutionary process of the dispersion of Gondwana and the accretion of Asia accompanied by a southward migration of its orogenic belts.

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