Characteristics And Cause Analysis To The North-South Fault Of Duohemao Area In Qinghai Province

Duohemao region locate in northeastern Tibetan Plateau, As the response to the collision between the Indian and Eurasian plates, a series of tectonic action was taken place in northeastern Tibetan Plateau after Mesozoic , which play a important role in the formation and evoiution of the S-N fault system in the Duohemao region.The S-N fault system Duohemao region lies in Zeku surname of Qinghai province, which is along to the western Qinling tectonic regimes. The fault system is 20 kilometers long, it includes four chief faults, which is located in east and west sides of Duohemao town. It dips to the west, part dip to east for the press force, the dip angle is rather steep. The fault controls the distribution of basalt and purple glutenite, and is the important fault controlling the basins of Duofutun.The S-N fault system is formed in the Cretaceous NS compressive stress tectonic settings of the west Qinling. The paper analyze the fault's geometry, kinesiology, dyn features in detail; divided the fault into three cycles: the first one is normal fault, the second is reverse fault; and the third is the reverse fault become active again; expatiate the formation and evolution of this fault as well as the relations with the uplift of Tibetan Plateau by the means of field mapping and profile survey etc.Form the field observation; the faults control the formation and evolution of Duofutun Basin, and basalt interbed with purple glutenite in Duofutun Basin, so we can deduce that first phase of the faults with the formation of basalt in the same period or slightly earlier. Combining with the former research of dating data to the basalt in this region and the uplift of the north-east edge of Tibetan Plateau we can deduce the time of the normal fault formation is Early Cretaceous, about 112 Ma, and the reverse thrust take place in the Eocene,the third occur in the Pliocene.