Cenozoic lithospheric extension and thinning of North China：Mechanism and process

Abstract： Two lithospheric-scale tectonic units may be distinguished in North China： the circular North China rift and its surrounding mountain ranges in the east and the Ordos cratonic block and its surrounding elongated down-faulted basins in the west. The former consists of the main quasi-circular basins and surrounding ranges, as well as the mountain ranges in Jiangsu and Shandong in the central part of the large quasi-circular basin. The North China rift basins formed mainly by pure shearing and distributed shearing (both of which contain simple shear components) deformation mechanisms during the Paleogene and Neogene-Quaternary respectively. They originated by the combined action of the uplift of the Ordos cratonic block and NE-directed compression on the Liupan Mountains at the southern margin of Ordos from the Qinghai-Tibet Plateau collision zone. In the Cenozoic, during the rapid extensive lithospheric thinning, the rate of the E-directed extension in the eastern North China region was much higher than that in the Ordos block in the west, which implies that the eastward flow of the asthenospheric material may have actively dragged the overlying lithosphere eastward. There might be three passageways to allow the eastward flow of the asthenospheric material below the Qinghai-Tibet collision zone： (a) from the southern part of the plateau through Songpan-Garzê and Sanjiang (which refers to the Lancang, Nujiang and Jinsha rivers flowing in eastern Tibet, southwestern Sichuan and western Yunnan) to the South China Sea, (b) from the northern part of the plateau through the Liupan Mountains, peripheries of Ordos and Northeast China plain to the Sea of Japan, and (c) from Pamir through the Tianshan Mountains, western Mongolia and Baikal to the Okhotsk Sea.