Abstract:

In China,some subduction zones are quite different from A.W.Bally's A/B-subduction.They have,as usual,huge thickness of Meso-Cenozoic prism of sediments in the front of folded mountain chains with a little or no sub-marine facies.They are far away from,and not related kinetically with B-subduction.At first,they were normal faults,but changed later into reverseones or thrusts near the earth surface.Hence,the author proposes in this paperthat these zones could be termed as C-subduction,i.e.,China-type subduction which can be exemplified by Karamay-Urho thrust system in the northern margin of Junggar Basin and the Longmenshan thrust belt in Sichuan Basin.As for the mechanism of formation of the C-subduction,it is assumed that it was possibly formed in the front of the older Paleozoic folded mountain chain or at the margin of the Meso-Cenozoic basin,where huge column of sediments accumulated,thus ensuring great instability under sedimentary load.As long as the plate action in the distance took place,these basin floors could be inflaenced and certainly be underplated towards the folded mountain chains or the uplifted basin margins because the potential energy of the loading turned into kinetic energy,thus consequently resulting in the above mentioned C-subduction.The mechanic model is similar to that of K.O.Emery (1980),i.e.in actions of sedimentary loading,the margin of stable continent could changed into unstable continent margin.Conditions for hydrocarbon generation and preservation in the thrust belts of C-subduction are very complicated but very promising.The first important factor for petroleum prospecting is the existance of rich source rocks,and the relative stability of earth crust in late stage is also indispensible for petroleum preservation.