| 中国的蓝片岩 |
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| BLUESCHIST IN CHINA |
| Blueschist, as a rock record of plate tectonics, has been seen in some main orogenic zones or suture zones in China, including from north to south1) Western Tianshan blueschist in Xinjiang, 2) Southwestern Junggar blue-schist in Xinjiang, 3) Ondor Snm blueschist in Nei Mongol, 4) Solonshan blueschist in Nei Mongol, 5) Northern Qilianshan blueschist in Qinghai, 6) Eastern Qinling blueschist in Shaanxi, 7) Tougbaishan blueschist in Henan, 8) Ailaoshan blueschist in Yunnan, 9) Lancangjiang blueschist in Yunnan, 10) Middle segment of Yarlung Zangbo River blueschist in Xizang (Tibet), and11) Yuli blueschist in Taiwan. The occurrences of these blueschists show the basic outline of plate tectonics in China.The metamorphic ages of blueschists around the Sinokorean-Tarim plate range from Caledonian to Variscian of Paleozoic, while those around the South China plate are of the Mesozoic and Cenozoic. Their evolution and relations with time reflect the model of continental accretion and the essential course of plate tectonic evolution in China.Except for the northern Qilianshan blueschists consisting of typical gla-ucophane schist and mineral assemblage, the mineral assemblage in other blueschist belts are almost crossite + stilpnomelane + phengite±chloritoid; the diagnostic minerals like jadeite (or jadeitic pyroxene) + quartz, lawsonite, aragonite are rarely developed. Glaucophanic minerals are generally crossite, magnesioriebeckite and barroisite according to the classification of amphibole group adopted by IMA-CNMMN, but lacking glaucophane. Jadeitic pyroxenes are mainly found in the "C" type eclogite of northern Qilian Mountain and the Tongbai Mountain and metamorphic gabbro of Kenanl lawsonites have been recognized in the Yarlung Zangbo River and the Ondor Sum blueschist belts; and phengites are distributed commonly in every blueschist belt.The blueschist rock types are dominated by glaucophane bearing metamorphic basic volcanics like chlorite-epidote glaucophane schist, glaucophane schist or glaucophane-bearing greenschist, with small amounts of metamorphic pelite and silicilith such as glaucophane-quartz schist, stilpnomelane-chlorite sericite schist and phengite sericite schist.The "C" type eclogite closely related with blueschist occurs in the northern Qilian Mountain and the Tongbai Mountain.All the blueschist belts belong to the high P/T facies consisting of glaucophane schist and greenschist facies. Many blueschist belts are accompanying with the high T/P belts, and commonly made up of paired belts.Blueschists are generally associated with ophiolite, some of which are part of ophiolite suites themselves. Most blueschist strata seem to be oceanic crust sedimentary formation, which consists of abyssal silicilith and basic volcanics intercalated with beds of graywacke. The tectonic melanges are developed almost in every blueschist belt, where the blueschist occurs as native or exotic blocks with blocks of ophiolite in the matrix. In such a case, it is very difficult to identify the relationship and boundary between the blue-schist, ophiolite and melange. There are very little intermediate-acid mag-matic activity of the same age in the place where blueschists are well developed.Formed at special geotectonic sites and effected by tectonic chaotic, the blueschists generally show stronger deformation and fragmentation both in microcosmic texture and macroscopic occurrence. In the macroscopic aspect, occurring as the tectonic blocks and lenticular bodies in matrix, they rarely have a contineous section. In the microcosmic aspct, their rock-forming minerals like glaucophane, often show the strain and ring textures. The para-genetic minerals are all of disequilibrium, indicating recrystallization under lower temperature and higher pressure.This paper also describes the general feature in each blueschist belt in the light of occurrence, mineral assemblage, rock type, metamorphic facies and facies series and age. Their origins and plate tectonics significance are discussed from the regional geological setting. |
| GAO Yan-lin.1984.BLUESCHIST IN CHINA[J].Acta Geoscientica Sinica,6(3):61-76. |
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