Investigation On The Liao Nan Indosinian Extensional Tectonics

The LiaoNan Indosinian Extensional Tectonics is located in the southeastern margin of North China plate, and in the east of the Tanlu Faults zone, which is the preliminary deformation of the sedimentary cover in this region. Based on 1:50 000 scale regional geological survey, this paper has made a rather deep investigation on the geometric shape, deformation feature, deformation mechanism, deformation environment and kinematic characteristics of this tectonics. In the end, it also discusses the dynamic mechanism of this extensional tectonics and its function in the tectonic evolution of North China. The methods used in this paper are those like macro- and micro-deformation observation, fabric analysis, strain measurement and isotopic dating, all conforming to the primary idea of regional structural analysis.The LiaoNan Indosinian Extensional Tectonics is composed of two structural units, namely the original system and the alien system. The original system is the crystallized basement of this region, on the top of which has developed a nearly horizontal ductile shear zone. The alien system is the late proterozoic-paleozoic sedimentary cover, which is subdivided into two parts, according to differential deformation and metamorphism, namely the lower ductile deformation massif and the upper brittle deformation massif. The extensional tectonics is characterized by the two-unit and three-horizon structure.This extensional tectonics has deformed vertically, composing of three structural horizons with age from old to young, namely the lower base in ductile shear zone, middle ductile deformed massif, and upper brittle massif. The relevant structural rocks distribute in the related horizons.The strain measurement results indicate that the mechanism of deformation of this extensional tectonics is simple shear whose deformational environments change vertically in a sequence of mid-high greenschist facies, low green schist facies, mid-low greenschist facies, low green schist facies and brittle shear deformation facies. Regional dynamic metamorphism was associated with the deformation.Both macro- and micro- oriental marks indicated that the extensional tectonics has extended from SEE to NWW, with a slipping distance of at least 27.39 km. The earth Crust has become thin in thickness vertically, and extended in width.The extensional tectonics was formed in mid-Triassic determined by isotopic dating and geological events. The driving force may originate from the thermal uplift of the east part of the studied region due to the Indochina magma tic activity. The extensional tectonics is common in the process of basin-mountain transformation, as indicated by a large number of facts.