Late Mesozoic Tectonostratigraphic Evolution Of The Northeast China And Adjacent Regions

Northeast China and adjacent regions,encompassing the southern fringe of the Siberia Block,the eastern Central Asian Orogenic Belt and the northern fringe of the North China Block,are one of the most complex geologic provinces on earth.It is made up of a collage of terranes,which accreted before the early Mesozoic.During the late Mesozoic,widespread magmatic events and a significant number of sedimentary basins,metamorphic core complexes and fold and thrust belts developed in this region,recording intense intracontinental deformation and having attracted much attention.However,the sedimentary and tectonic evolution of the Northeast China and adjacent regions remains highly contentious,especially the sedimentary basins formed in this region during the Jurassic-Cretaceous.The Mohe Basin and the Erlian Basin contain thick Jurassic-Cretaceous sediments and provide excellent opportunities to understand intracontinental deformation in Northeast China during the late Mesozoic.In order to clarify the sedimentation and deformation features of Northeast China and adjacent regions during the late Mesozoic and decipher corresponding driving mechanisms,detailed sedimentary,structural,geochronological,and thermochronological studies have been conducted in the Mohe Basin and the Erlian Basin.Furthermore,an overall review for the Middle Jurassic-Cretaceous tectonics in Northeast China and adjacent regions by considering the tectonostratigraphic evolution of the Mohe and Erlian basins and other lines of evidence is given to understand the late Mesozoic tectonic evolution of the Northeast China and adjacent regions.The Mohe-Upper Amur Basin located in the northern part of the Northeast China and adjacent regions,is crossed by the Russia/China border,and its Chinese and Russian parts are known as the Mohe Basin and Upper Amur Basin,respectively.Using most up-to-date data on stratigraphy,sedimentology,petrography,and detrital zircon U-Pb geochronology,the present thesis establishes the stratigraphic correlation between the two,Mohe and Upper Amur parts of the Mohe-Upper Amur Basin,and analyzes depositional ages,provenance,and paleogeography of their Jurassic-Lower Cretaceous strata.The adopted Middle-Late Jurassic ages for the Xiufeng,Ershierzhan,Emuerhe,and Kaikukang formations in the Mohe Basin,are revised and constrained to late Kimmeridgian(ca.155-152 Ma),Tithonian(ca.152-145 Ma),Berriasian-early Valanginian(ca.145-137 Ma),and late Valanginian(ca.136-133 Ma)ages,respectively.During deposition of the Xiufeng and Ershierzhan formations(late Kimmeridgian-Tithonian),extension occurred in the Mohe-Upper Amur Basin,and sediments were mainly sourced from areas to the south of the basin.Later,during the deposition of the Emuerhe Formation(Berriasian-early Valanginian),the northernmargin of the Mohe-Upper Amur Basin was uplifted and started furnishing sediments into the basin.During the deposition of the Kaikukang Formation(late Valanginian),regional uplift of the northern part of the Mohe-Upper Amur Basin transformed the basin into a compressional intermountain basin,with sedimentation localized in its southern part.After the deposition of the Kaikukang Formation,extension and associated volcanism occurred in the basin.The Erlian Basin is situated in the middle and western area of the Northeast China with over 1000 km far away from the active plate boundaries where the oceanic Pacific Plate subducts beneath the Eurasian Plate.Based on 13 newly-obtained zircon U-Pb ages for the Jurassic-lowest Cretaceous strata in the Erlian Basin,the correlation of Jurassic-lowest Cretaceous strata between the Erlian Basin and the Yan Shan is reestablished and a high-precision chronostratigraphic framework is presented for the Jurassic-lowest Cretaceous strata in the Erlian Basin.The Aqitu-Qiha formations are refined to the Aalenian-early Bathonian(ca.174-167 Ma)in age,the Xing'anling Group is refined to the Oxfordian-early Kimmeridgian(ca.163-153 Ma),the Hugejiletu Formation is refined to the Tithonian-early Valanginian(ca.151-139 Ma),and the Aershan Formation is refined to the Valanginian-?(? ca.138 Ma).Combined with 6 newly-obtained fission-track data and seismic reflection profiles,the Jurassic-earliest Cretaceous tectonostratigraphic evolution of Erlian Basin is reconstructed and five major phases of deformation are revealed.These deformation phases include early Middle Jurassic(Aalenian-early Bathonian,ca.174-167 Ma)initial extension,late Middle Jurassic(late Bathonian-Callovian,ca.166-164 Ma)compression,early Late Jurassic(Oxfordian-early Kimmeridgian,ca.163-153 Ma)extension,latest Jurassic-earliest Cretaceous(late Kimmeridgian-early Valanginian,ca.153-138 Ma)compression,and Early Cretaceous(after early Valanginian,? ca.138 Ma)extension.A significant structural inversion occurred in the Erlian Basin during the mid-Cretaceous.On the basis of detailed stratigraphical,sedimentological and structural analyses,the present thesis reveals that a NW-SE compressional deformation occurred in the Erlian Basin between the depositions of the Lower Cretaceous Saihantala and Upper Cretaceous Erlian formations,causing intense folding of the Saihantala Formation and underlying strata,and the northwestward migration of the depocenters of the Erlian Formation.Using 3 newly obtained detrital zircon U-Pb ages and previously published paleomagnetism-and fossil-based ages,the Saihantala and Erlian formations are suggested as latest Aptian-Albian and post-early Cenomanian in age,respectively,implying that the inversion in the Erlian Basin occurred in the early Late Cretaceous(Cenomanian time).Apatite fission-track thermochronological data record an early Late Cretaceous cooling/exhuming event in the basin,corresponding well with the aforementioned sedimentary,structural and chronological analyses.Combining with the reestablished late Mesozoic tectonostratigraphic evolution of the Mohe Basin and the Erlian Basin,and previously published stratigraphical,sedimentological,structural,geochronological,geochemical,and geophysical data of other basins and fold and thrust belts,the present thesis makes a review for the Middle Jurassic-Cretaceous evolution of the Northeast China and adjacent regions,and proposes a six-stage tectonic evolution of the Northeast China and adjacent regions.During the early Middle Jurassic,the Northeast China and adjacent regions were predominated by extensional regime,which led to the initial formation of numerous rift basins along the Mongolia/China border,and was probably induced by post-orogenic gravitational collapse after the closure of the western Mongol-Okhotsk Ocean.During the late Middle Jurassic,this region was predominated by compressional regime,which resulted in the widespread sedimentation hiatuses,accumulations of synorogenic conglomerate-dominated successions,and angular unconformities,and was likely driven by the far-field effects of the Karakoram/South Pamir collision.During the early Late Jurassic,this region was predominated by extensional regime,which caused the reactivation of rift basins,and was probably related to the northeastward escape tectonics in Northeast Asia driven by the continuous Karakoram/South Pamir collision.During the latest Jurassic-earliest Cretaceous,this region was predominated by compressional regime,which gave rise to the extensive formation of sedimentation hiatuses,angular unconformities,folds and thrusts,and the accumulations of thick synorogenic conglomerate-dominated successions,and was probably resulted from the combined effects of the collision between the Kolyma-Omolon composite terrane and the Siberia Craton,the collision between the Siberia Craton and the Amuria Block following the closure of the eastern Mongol-Okhotsk Ocean,and the far-field stresses of the collision between the Lhasa Block and the Qiangtang Block.During the Early Cretaceous,the region was predominated by extensional regime,which resulted in highly intense bursts of magmatic activities,rift basins and metamorphic core complexes,and was possibly caused by the recession of the Siberia/Amuria collision and the reactivation of post-orogenic gravitational collapse.During the early Late Cretaceous,the region was significantly affected by a compressional event,which 'produced intense inversion of pre-rifting structures and tectonic uplift,was probably resulting from the Okhotomorsk Block-East Asia collisional event at about 100-89 Ma.