The Structural Features And Significances Of Argun Ductile Shear Zone And Cuo Gang Tectonic Gneiss Zone

Argun ductile shear zone distributed in the north of Argun fault, diverged along northeastward. Argun ductile shear zone is composed of granitic protomylonite, mylonite foliation strikes NE and dips NW mainly, the dip angle is low from 8°to 30°. There is mineral stretching lineation which strikes NE too on the foliation, the dip angle is low from 7°to 29°. It reflects that the mylonite suffered from the ductile shearing action at low angles.Mylonite in Argun ductile shear zone exists the appearance of rotational porphyroclast, S-C structural fabrics and elongated orientation of the feldspar. The special microstructure of mylonite such as mylonitic texture, S-C structural fabrics, rotational porphyroclasts, core-mantle structure, domino structure and elongation of feldspar is very common. By the estimation from the matrix mineral combination, deformation behavior of the quartz and the feldspar, it can be concluded that the deformation temperature of the mylonite is range from 400 to 500℃. At the basic of the geological observation in the wild and the referring to the reported research outcomes, the author thought that Argun ductile shear zone formed at the late stage of Late Jurassic. By the research of Flinn-diagram of oriented samples from the mylonite, it can be concluded that Argun ductile shear zone formed in the background of spreading tectonics.Cuogang extensional deformation zone is distributed at the area of Derbugan fault, its strike is accordence with Derbugan fault's, geological and geophysical characteristics are significant. The extensional deformation zone is composed of tectonic gneiss, so it is also called Cuogang tectonic gneiss zone.Tectonic gneiss foliation dips NE-SE maninly, the dip angle is from low to medium; lineation pitch direction is accordence with foliation dip basically, pitch angle is low. The characteristic structuralfabric of tectonic gneiss such as dissymmetrical plastic flow fold, the band and ribbon structure, tetano-gneissosity is common. tectonic gneiss owns some microstructure features such as multi-crystal quartzose band, the three edges equilibrium texture and the multi-crystal augen structure which are different from mylonite.the band is formed by the grain after it generated plastic flow, Due to the effect of the structure transformation,the band become the dissymmetrical plastic flow fold; multi- crystal quartzose band is the result of two recrystallizations,the first is dynamic recrystallizations, the second is static recrystallizations; the three edges equilibrium texture of strain in quartz grains.is the result of static recrystallizations.Cuogang tectonic gneiss is formed by tectonic ductile belt in deep deformation level. In the deep crust,the neutral- light felsic band in the tectonic ductile is the product of the rock which get metamorphic deformation reform experience and partial melting, make the original rock material compositionin differentiation and readjustment at space under high temperature. The tectonic gneiss is formed at deep crustal-tectonic levels, mainly accompanied by decompressional melting of the rock, grain flow and diffusion creep mechanism.The regional geochemical characteristics of volcanic and intrusive rocks and the emplacement of basic dike swarms in the research area and its neighboring area indicated that the area is in the tectonic setting of regional extension in in J3-K1; There are a large number of metamorphic core complex rocks in the area of Argun, Great Xing'an around Argun, border regions between China and Mongolia, China and Russia, The formation time of metamorphic core complex is similar to Argun ductile shear zone and the Cuogang extensional deformation zone. Metamorphic core complex rock appear represents a regional tectonic background of stretching. There are many medium and small sized fault basins which formd in K1 in Northeast Asia, they formed in the background of strong crustal extension. These are also accord with Argun ductile shear zone and the Cuogang extensional deformation zone. In a word, based on geological section measurement and laboratory study, the author confirmed Argun ductile shear zone and the Cuogang extensional deformation zone are the products of the regional extension background in J3-K1.From the above, based on the research findings given by previous researchers, the author studied Argun ductile shear zone and tectonic gneiss zone in details with lessons and experiences accumulated in work and practice, researched their structural characteristics, analysed the forming time and formation of regional tectonic background, etc. summarized the features of mylonite and tectonic gneiss for identification.