Abstract:

The formation and evolution of a basin is related closely to evolution of the dynamic system in the deep of the earth. The dynamic system mainly consists of the lithosphere, the asthenosphere and the Moho. The thickness of the lithosphere, effective elastic thickness and flowability decide tectonic and thermal artivities and theion, control the depth of detachment, thect thermal texture and architectural types of the basin. The asthenosphere does not only corrode the bottom of the lithosphere, but also affect direcily its thermal property. The Moho is a mobile inteiface. On the whole, it reflects the crustal architecture of different tectonic units; microscopically, it indicats basin-forming model. In North China,a lot of fault-depressed basins formed from Early-Middle Jurassic to early Early Cretaceous and a large depressed basin formed in the late Early Cretaceous in Shongliao Region. These basins are distrituted regularly along Shedao BasinNorth Liaoning-West Liaoning, and hydrocarbons-bearing property changes from gas-bearing fault-depression to depression without oil, until at last fault-depression with no oil and gas at all. This seems to be related to the types of basins, but acturally it is controlled by dymamic systems in the deep of the earth. The main facts are as follows:(1)The lithosphere thickness is about 50～60 km in Shongliao Basin, 25 km thinner than that in West Liaoning. This indicates that the thicker the lithosphere is, the deeper the detachment belts will be, and the bigger the intensity of the lithosphere will be. The intensity of the lithosphere in Shongliso Basin is lower than that in West liaoning. (2)Since there are considerable differences in the basements of the basins, geothermal structure in Shongliao Basin is different from that in West Liaoning. The mantle heat flow Qr=58.1 mW/m² in Shongliao Basin, Qr/Qs=77%,and the mantle heat flow is only 36.8 mWm²,Qr/Qs=59% in West liaoning. The temperabe of crust-mantle boundary in Shogliao Basin(744.4℃)is higher than that in West Liaoning(644C).The geothermal structure is the basic role that caused thermal subsident differences between Shongliao Basin and West Liaoning region.

Key words: basin, geodynamics, system, lithosphere, detachment zone, asthenosphere, Moho