Western Block of the North China Craton
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The Western Block of the North China Craton is an ancient micro-continental block mainly composed of Neoarchean and Paleoproterozoic rock basement, with some parts overlain by Cambrian to Cenozoic volcanic and sedimentary rocks.[2] It is one of two sub-blocks (the Eastern Block and the Western Block) within the North China Craton, located in east-central China. The boundaries of the Western Block are slightly different among distinct models, but the shapes and areas are similar. There is a broad consensus that the Western Block covers a large part of the east-central China.[1][3][4][5][6][7]
Igneous, sedimentary and metamorphic rocks are present in the Western Block. The oldest geological records in the Western Block are 2.7 billion-year-old intrusive igneous rock found in Xiwulanbulang in Inner Mongolia.[8] The youngest rocks are 23-million-year-old extrusive igneous rocks, which are located in Sanyitang (in Hebei) in the orogenic belt across the block.[9] The sedimentary rocks distribute predominantly in the Ordos Basin located in the south of the Western Block.[10] Exposures of metamorphic rocks are mostly scattered in the north of the block.
The tectonic setting and evolution of the Western Block are debated. There are various models hypothesizing the subdivisions and tectonic history of the block and they are generally mutually exclusive. However, most models agree with the presence of a Paleoproterozoic orogenic belt cutting across the Western Block in the east-west direction, despite having various names for it.[10]
Since the geological events of the Western Block started in Precambrian time, when more than 80% of the present volume of continental crust formed,[11][12][13] complex geological evolution and early tectonic history can be studied through the geological records in the Western Block.[14][15]