THE HISTORY OF GENERATION,DEVELOPMENT AND EVOLUTION OF THE TANCHENG-LUJIANG FRACTURE IN LIAONING PROVINCE

The Tancheng-Lujiang fracture includes a series of NE-NNE-trending fractures, which form a fracture system running obliquely through the marginal-Pacific tectonic domain in. the eastern part of China.It has a long history of generation, development and evolution and has exerted different controlling effects on sedimentary formations, magmatic activity, structural deformation and metamorphtsm in different geological periods of time.Extending from Shandong to Liaoning and then past Shengyang northwards,the fracture has left different traces in different geological periods of time. The major fracture of the Tancheng-Lujiang fracture——the Yingkou-Dongerbao-Hunhe fracture——appeared in the early Precambrian.During the late Precambrian the Tancheng-Lujiang fracture developed,resulting in the tectonic framework characterized by an uplift being sandwiched by two depressions in the lower reaches of the Liaohe River. The eastern and western depressions controlled the deposition of the upper Precambrian of Liaodong and Yanshan types, respectively. The Hunhe fracture became the boundary between the two above-mentioned types of upper Precambrian. In Paleozoic times, the Tancheng-Lujiang fracture developed and became mature. Its eastern branch rejuvenated and controlled the Paleozoic deposition. Extending northwards beyond Shengyang it was divided into two branches: one stretched past the Yunhe River northwards, forming the Dunhua-Mishan fracture,and the other was the Yilan-Yitong fracture. They were formed attendant with intrusion and folding and deformation of paleozoic granite. In the Indosinian time the eastern branch——the Yingkou-Dongerbao fracture and the Dunhua-Mishan fracture——inherited the activity of the former period. The eastern side sank and the Hunhe-Taizihe depression became a Triassic inherited basin. In Yanshanian time,the Tancheng-Lujiang fracture extended beyond Shengyang, forming the Changchun-Siping fracture. The strata containing the Rehe biotas at the western side constitute an important coal-bearing formation, while the contemporaneous formation at the eastern side possesses the same sequence, but bears no coal measures. In the Cenozoic the Tancheng-Lujiang fracture rejuvenated and there appeared new branches. In the Paleogene,the Shaling-Erjiagou fracture （in the east） and the Tai’ an-Dawa fracture （in the west）originated;the volcaniclastic formations in the eastern and western lower Liaohe River depressions extended northwards into the Yilan-Yitong graben and the Hunhe-Dunhua-Mishan graben, respectively. In the Neogene-Quaternary the western block of the eastern branch——the Yinkou-Dongerbao fracture and the Changcun-Sipin fracture——sank and becamea plain, while the eastern block rose and became hills and mountains. The Tancheng-Lujiang fracture in Liaoning dissects the lithosphere and extends deep into the upper mantle, so is called the translithospheric fracture. It has controlled the distribution of kimberlite and is a highly active seismic belt. The regional structural units——uplifts and depressions——at both sides correspond to each other, with small horizontal displacements. Its structural characteristics are similar to those of the Yishu fracture. In the process of its generation, development and evolution, the stress field of the Tancheng-Lujiang fracture has been repeatedly subjected to N-S counterclockwise shearing and clockwise shearing as well as NW-SE compression and extension. In the Archean-early Proterozoic,the extensional stress field caused the west to rise and the east to sink. The late Proterozoic crust was downwarped and deformed in the N-S counterclockwise shearing stress field, causing the west to sink and the east to rise. In the Paleozoic the north China platform rose in the east and sank in west or in a reverse direction under the repeated N-S extensional-compressional stress field. The Jilin-Heilongjiang geosyncline became the boundary of the lithofacies formation with the eugeosyncline; meanwhile, there occurred planar granite batholiths. In the late Yanshanian time, the alternating action of the E-W extensional-compressional stress field resulted in volcanic eruption and accumulation of coal measures and tilting of basement. In the Paleogene, as the N-S clockwise shearing tectonic field generated NW-SE extension, the eastern and western Lower Liaohe depressions further broadened and new fractures appeared. Continental basalts outpoured and oil-bearing clastic rocks were accumulated. In the Neogene-Quaternary,under the N-S counterclockwise shearing stress field, the Neogene was folded in a NE direction, the Songliao-Lower Liaohe plain was downwarded and the Zhangguangcai Mountains, Changbai Mountains and Liaodong Peninsula uplifted, thus forming the present-day landscapes.