| 西藏雅鲁藏布江中段构造混杂带特征及其构造意义 |
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| THE FEATURES OF MELANGE ZONE IN THE MIDDLE SEGMENT OF THE YARLUNG ZANGBO RIVER AND THEIR PLATE TECTONIC SIGNIFICANCE |
| This paper deals chiefly with melanges in the middle segment of the Yarlung Zangbo (Tsangpo) River in southern Xizang(Tibet). The characters, origins and tectonic significance of each melange type will be further discussed.The various melanges in the middle segment of the Yariung Zangbo suture can be divided into two types: serpentinite melange and argilloarenaceous melange, which form a paired melange belts parallel to the suture zone. They respectively represent the mixing character and model of plate tectonics.1. Serpentinite melange zone: It is about 500 km long and mainly occurs in the Xigaze-Ngamring area. Its southern boundary is commonly in fault contact with the J3-K1 strata and the northern boundary is transitional to the overlying ophiolite or in fault contact with the latter in some places.The matrix of these melanges is made of serpentinite and serpentinized harzburgite showing strong plastic deformation. There are many native fragments (blocks) such as harzburgite, dunite and rodingite, and a lot of exotic blocks of metagabrro, diabase, schist, garnet-amphibolite, limestone, chert, hornblende-schist etc.. These exotic blocks apparently show shear deformation after mixing. Some of them contain high-pressure metamorphic minerals. These melanges might have been formed either by subduction or by collision.2. Argillo-arenaceous melange zone: This is distributed in the south of the suture zone and may be further divided into two subzones according to the character of matrix and its distribution. The matrix includes flysch or subflysch sediments of the Triassic-Cretaceous. The northern subzone which forms the main part of the middle segment of the melange zone, occurs adjacent to the region near the ophiolite zone. The matrix consists of sandy shale and sandstone of Triassic-Cretaceous age, which are strongly deformed and show broken stratification. Where there are many exotic blocks of ultrabasic rock and chert from the ophiolite complex and limestone from the Lower Permian, a lot of blocks or fragments of sandstone, chert and limestone of Triassic-Cretaceous age are probably native blocks.The southern subzone appears in the region far south away from the suture. The matrix is composed mainly of flysch sediments of the J2-K. Deformation of the matrix and blocks is not intense. No ophiolite blocks have been seen.The degree intensity of deformation of the melanges in the middle segment of the Yarlung Zangbo River increases from south to north. The age of these melange zones is also discussed in the paper. |
| GAO Yan-lin,TANG Yao-qing.1984.THE FEATURES OF MELANGE ZONE IN THE MIDDLE SEGMENT OF THE YARLUNG ZANGBO RIVER AND THEIR PLATE TECTONIC SIGNIFICANCE[J].Acta Geoscientica Sinica,6(1):1-20. |
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