| The Da Hinggan Mountains are located in the eastern segment of the Central Asian Orogenic Belt and has experienced a complex collage process of microplates and the superposition and transformation of different Mesozoic tectonic domains.It is a prominent geomorphic marker of NE China,although its evolution history and Mesozoic uplift mechanisms remain equivocal.The multi-stage Mesozoic Magmatic events and the large-area metamorphic and deformed"ancient basement"rocks in the Da Hinggan Mountains are the key to reveal the evolution of the Da Hinggan Mountains,especially the uplift history since the Mesozoic era.In this paper,the Keluo Complex exposed in the northern segment of the Da Hinggan Mountains is taken as the research object.We present results from a comprehensive study on the field and micro-structures,kinematics,rheology,quartz EBSD fabrics,geochemistry and geochronology of the Keluo Complex,and find out the protolith properties and deformation phases of the Keluo Complex.Further,the evolutionary history and uplift mechanism of the Da Hinggan Mountains are discussed.It provides more geological evidences for revealing the superposition and transformation processes of Mesozoic multi-tectonic domains in NE China.The latest chronological results show that the Keluo Complex is a complex collage with diverse Permian to Mesozoic protolith ages rather than the Precambrian or pre-Ordovician basement of the Xing'an massif as it was previously envisaged.The Keluo Complex may have been first formed in the Early Carboniferous,then experienced multiple magmatic events from Early Permian to Middle Jurassic(299.0?175.5 Ma),and was finally superimposed and transformed by magmatic and tectonic activities during the Late Jurassic(152.0?157.7 Ma)and Early Cretaceous(118.3 Ma).Geochemically,the Early Permian granitic mylonites have high Si O2,Al2O3 and total alkali concentrations,and low TFe O,Ni,Co and Mg O concentrations,indicating that its primary magma may be derived from the partial melting of the lower crust and formed in a post-collisional extension environment,which is related to the collision of the Xing'an and Songnen massifs.Early Mesozoic granitic mylonites and gneiss have high Si O2,Al2O3 and total alkali concentrations,characterized by the natures of metaluminous to peraluminous and high-K calc-alkaline series.The samples are relatively enriched in large-ion lithophile elements,depleted in high-field-strength elements,and exhibit low Cr,Co,Ni and Mg O concentrations,suggesting that derived from magma generated by partial melting of the continental crust within an active continental margin setting related to the southward subduction of the Mongol-Okhotsk Ocean.Based on detailed the field and micro-structures analyses,two prominent deformation events(D1 and D2)were recognized in the Keluo Complex,which occurred in the Late Jurassic and the middle and late Early Cretaceous.The D1 is dominated by SW-trending sinistral ductile shearing accompanied by moderate to high-temperature deformation(500?600°C)resulting from NW–SE compression.The deformation strain rate is relatively high(4.48×10-12?8.74×10-15 s-1),and there is not only general shear dominated by pure shear,but also general shear dominated by simple shear.The deformed rocks are mainly S-L and S tectonites.The D2 is a bi-directional extensional and detachment deformation corresponding to a low temperature(300?400°C)and low strain rate(1.20×10-14?4.54×10-20 s-1)deformation developed at a shallow-level ductile regime resulting from NW–SE extension.The deformed rocks are mainly L=S tectonites,which are formed under the general shear dominated by pure shear.The deformation ages,deformation characteristics and deformation mechanisms of the two deformation events all show significant differences,suggesting that they may be formed in different tectonic settings.Combined with previous research results,the D1deformation was influenced by subduction and closure of the Mongol-Okhotsk Ocean.At this time,the lithosphere was compressed and thickened,accompanied by the emplacement of deep magma,and the Da Hinggan Mountains began to uplift.The D2deformation is correlated to the superposition of the extension after the closure of the Mongol-Okhotsk Ocean and the rollback of the Paleo-Pacific Plate.The lithosphere was thinned on a large scale,which led to the continuous uplift of the Da Hinggan Mountains. |
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