| The spatial-temporal extent and influence of the Mongol-Okhotsk and Paleo-Pacific tectonic regimes in northeast?NE?China and adjacent areas during late Mesozoic times have long been controversial.As a superimposed rift system which formed under the ground of extensive intracontinental extension during Late Jurassic to Early Cretaceous,Hailar-Tamtsag basin is a key area to study the relationship between the Mongol-Okhotsk and Paleo-Pacific tectonic regimes and their superposition.With the aim to constrain the evolution of those two regimes,in this paper,the Tanan depression,which is a second-order structural unit in the western part of Hailar-Tamtsag basin,is taken as the research object.On the basis of structural analysis of three-dimensional?3D?seismic data in the Tanan depression,and taking into account the controlling effect and influence of the pre-existing facies on the basin evolution,the deformation events in the Early Cretaceous can be subdivided into four periods:?1?stage of NW-SE trending extension during the deposition of the Tongbomiao Formation to the upper part of the second Member of the Nantun Formation,a series of depression-controlled NE-trending normal faults and extensional structural style combinations formed;?2?stage of NE trending compression during the deposition of the upper part of the second Member of the Nantun Formation to the first Member of the Yimin Formation,the compressions led to the inversion of some depression-controlled normal faults,and a NE–SW trending fault-propagation folds developed in the southeast of the depression in response to ongoing shortening;?3?stage of near EW trending extension during the deposition of the second member to the lower part of third member of the Yimin Formation,in addition to the original NE-NNE spreading depression-controlled boundary faults reactivated by transtension,a large number of NWW and near NS-trending normal faults were formed,thus producing a series of transtension structural styles;?4?Stage of near EW trending compression during the deposition of the upper part of the third Member of the Yimin Formation,the major faults of multi-stage active in the early stage once again underwent transpressional deformation,and the compressions also resulted in the absence of above T04 strata in the central and northern parts of the basin.During the formation of the basin,the influence of the inherited development on the structural characteristics of the basin is throughout.At the same time,the progressive development of tectonic effects in the same period and the superimposition of tectonic effects in different periods have also caused the continuous reorganization of the palaeogeomorphology,and thus dominating the change of the source system,the development of the sedimentary system,and the migration of the depocentres in the Tanan Depression.Additionally,We identify compressional structures in the basement in the southeast part of the depression,which is a key structural record that resulted from the Mongol-Okhotsk collisional orogeny during the Late Jurassic.Above five major deformational events make up a relatively complete tectonic deformation sequence of Hailar-Tamtsag basin.Moreover,the deformation sequence,together with other available information from the literature in NE China and adjacent areas,including petrology,geochemistry and geochronology data,also record the whole process from the orogenic stage after the closure of the Mongol-Okhotsk ocean,to the post-orogenic collapse of the Mongol-Okhotsk orogen,to the weakening of the influence of the Mongol–Okhotsk regime,and finally to be replaced by the Paleo-Pacific tectonic regime.Considering the superposition and transformation of the two tectonic regimes involves almost the whole geological process in NE China and adjacent area during the late Mesozoic,the complete geological record in the Tanan depression during this period provide new constraints on the research of regional tectonic evolution. |
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