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The Dabashan orocline is situated in the northwestern margin of the central Yangtze block,central China.Previous studies have defned the orthogonal superposed folds growing in its central-western segment thereby confrming its two-stage tectonic evolution history.Geological mapping has revealed that more types of superposed folds have developed in the eastern segment of the orocline,which probably provides more clues for probing the structure and tectonic history of the Dabashan orocline.In this paper,based on geological mapping,structural measurements and analyses of deformation,we have identifed three groups of folds with different trends(e.g.NW-,NE-and nearly E-trending folds)and three types of structural patterns of superposed folds in the eastern Dabashan foreland(e.g.syn-axial,oblique,and conjunctional superposed folds).In combination with geochronological data,we propose that the synaxial superposed folds are due to two stages of wNeS shortening in the west and north of the Shennongjia massif,and that oblique superposed folds have been resulted from the superposition of the NW-and NE-trending folds onto the early ～E-W folds in the east of the Shennongjia massif in the late Jurassic to early Cretaceous.The conjunctional folds are composed of the NW-and NE-trending folds,corresponding to the regional-scale dual-orocline in the eastern Sichuan as a result of the southwestward expansion of the Dabashan foreland during late Jurassic to early Cretaceous,coeval with the northwestward propagation of the Xuefengshan foreland.Integration of the structure and geochronology of the belt shows that the Dabashan orocline is a combined deformation belt primarily experiencing a twostage tectonic evolution history in Mesozoic,initiation of the Dabashan orocline as a foreland basin along the front of the Qinling orogen in late Triassic to early Jurassic due to collisional orogeny,and the fnal formation of the Dabashan orocline owing to the southwestward propagation of the Qinling orogen during late Jurassic to early Cretaceous intra-continental orogeny.Our studies provide some evidences for understanding the structure and deformation of the Dabashan orocline.
The Dabashan orocline is situated in the northwestern margin of the central Yangtze block, central China. Past studies have defned the orthogonal superposed folds growing in its central-western segment thus confrming its two-stage tectonic evolution history. Geological mapping has revealed that more types of superposed folds have developed in the eastern segment of the orocline, which probably provides more clues for probing the structure and tectonic history of the Dabashan orocline. In this paper, based on geological mapping, structural measurements and analyzes of deformation, we have identifed three groups of folds with different trends (egNW-, NE-and nearly E-trending folds) and three types of structural patterns of superposed folds in the eastern Dabashan foreland (egsyn-axial, oblique, and conjunctional superposed folds) .In combination with geochronological data, we propose that the synaxial superposed folds are due to two stages of wNeS shortening in the west and north of the Shenn ongjia massif, and that oblique superposed folds have been induced from the superposition of the NW-and NE-trending folds onto the early ~ EW folds in the east of the Shennongjia massif in the late Jurassic to early Cretaceous. conjunctionoral folds are composed of the NW-and NE-trending folds, corresponding to the regional-scale dual-orocline in the eastern Sichuan as a result of the southwestward expansion of the Dabashan foreland during late Jurassic to early Cretaceous, coeval with the northwestward propagation of the Xuefengshan foreland. Integration of the structure and geochronology of the belt shows that the Dabashan orocline is a assembled deformation belt for experiencing a twostage tectonic evolution history in Mesozoic, initiation of the Dabashan orocline as a foreland basin along the front of the Qinling orogen in late Triassic to early Jurassic due to collisional orogeny, and the fnal formation of the Dabashan orocline owing to the southwestward propagation of the Qinl ing orogen during late Jurassic to early Cretaceous intra-continental orogeny. Our studies provide some evidences for understanding the structure and deformation of the Dabashan orocline.