Abstract: In recent years, the relations between the large gasfields in West China and the evolutions of Tarim plate, Yangtze plate and Sino-Korean plate are paid close attention to. Following the failure of plate tectonic theory in the continents around the world, problems also arise from geologic phenomena that are associated with subduction zones including back-arc spreading, continental growth, recycling of crustal materials, mineralization and petroleum accumulation. This paper takes some large gasfields as examples to explain the natural gas generation is related with the deep crustal structures, especially with the low velocity-high conductive zone of the mid-crust, in which the natural gas can be synthesized by mantle fluids (CO2, CO, H2, etc.). Natural gas generation and distribution are in accordance with this hypothesis. According to this hypothesis, some new large gas fields are predicted.

Key words: plate structure, large gas field, gas generation, low velocity-high conductive zone, mid-crust