THE MESOZOIC TECTONIC FRAMEWORK AND EVOLUTION OF NORTH CHINA BLOCK

In the Mesozoic, the North China Block(NCB) was intensly reworked associated with the Yanshan Movement. At least two stages can be roughly divided for the tectonic evolution of this peiod, i.e. T1 - J2 intracontinental foreland basin in the southwest part of NCB related with the Paleo-Tethys orogenic belts, followed by the J3-K1 development of Eastern China Plateau and Yanshan-Yinshan thrusting belt. At T1-2, an intracontinental foreland basin with arc-shape began to develop along the southwestern part of NCB, caused by the compressive deformation along Helan Mt. Structural Belt in the west, and Qinlin Orogenic Belt in the southwest. The basin lately evolved into a widepread continetal basin bounded by a lower uplift in the northeast part of NCB. The Triassic tectonic-sedimentary framework lasted to the J1, with T-J depocenters mainly distributed in the southwestside of NCB. From J2 upward, many small-scale grabens began to occur in the eastern part of NCB. At the J2, the Palaeo-Pacific Oceanic Plate subducted obliquely underneath the Asia continent, which significantly changed the sedimentary framework of the NCB. Lately, a possible J3-K1 Eastern China Plateau(ECP) was uplifted rapidly, with emplacement of NE-trending granitic belt in the Taihang Mt. and formation of NE-NNE-trending folds. In addition, numerous NE- and NW-trending grabens of small scale occurred upon the ECP. The northern margin of NCB was uplifted strongly from J2 to J3. A J3 linear graben belt developed with deposition of coarse clastic sediments and eruption of volcanics, followed by thrusting of its basement. Regionally, it is suggested that the thusting episodes were caused by the distant tectonic effect from Mongolian-Okhotsk orogenic belt (J3-K1). A narrow continental basin continued to develop in the western part of NCB, which was lately reworked by thrusting belts surrounding the western part of NCB, especially in the northern side.