The Late Evolution History Of The Eastern Segment Of The Paleo-asian Ocean And Its Contribution To Mantle Modification Beneath The Northern Margin Of The North China Craton

Subduction is the most efficient mass and energy exchange transfer between the Earth’s layers.The northeastern margin of Eurasia is a classic area for exploring ocean-continent subduction and its effects on the geology and mineral resource during the Phanerozoic.The North China Craton(NCC)is a geological unit of this region that experienced the overprinting of the Paleo-Asian Ocean tectonic regime in the Paleozoic and the Paleo-Pacific tectonic regime in Mesozoic-Cenozoic.It has become an ideal area for exploring the superposition and transformation of multiple plate tectonic regimes.Recent studies of the Paleo-Asian Ocean tectonic system focused mainly on the history of tectonic evolution rather than deep crust-mantle interactions..The Permian-Triassic is a late stage of the evolution of the Paleo-Asian Ocean tectonic system,and the northern margin of the NCC is the critical area for the direct interaction between the Paleo-Asian Ocean and the NCC.This lead to questions such as: How does the southward subducting Paleo-Asian Ocean slab modify the mantle of the northern margin of the NCC with the gradual closure of the Paleo-Asian Ocean?What are the properties of metasomatic fluids in subduction zones?This paper reports on the evolution of the eastern part of the Paleo-Asian Ocean from the late Late Paleozoic to the Early Mesozoic by geochemical tracing using isotopes.The Permian-Triassic igneous rocks in the northern margin of the NCC,which were influenced by the evolution of the Paleo-Asian Ocean,were selected for this study.The modification from the subduction of the Paleo-Asian Ocean to the mantle beneath the northern margin of the NCC and its deep crust-mantle interaction has also been revealed.The main achievements are as follows:First,based on the spatial-temporal variations in the Permian-Triassic magmatism in the easternmost margin of the CAOB and the northeastern margin of the NCC,together with the detrital zircon chronology,the late evolution history and the final closure of the eastern part of the Paleo-Asian Ocean are revealed.1.The detrital zircon U-Pb geochronology of sedimentary strata exposed on the western margin of Khanka Massifwere sourced from the same area and were deposited during the Early–Middle Permian.Based on tectonic discrimination diagrams,we conclude that the western margin of the Khanka Massif was positioned in a convergent-boundary basin during the Early-Middle Permian,further indicating that the subduction of the Paleo-Asian Ocean was still ongoing at this time.2.Zircon U-Pb geochronology shows that the Permian igneous magmatism in the western margin of the Khanka Massif can be divided into three stages: Early Permian(281 ～ 273 Ma),Middle Permian(268 ～ 260 Ma)and Late Permian(257 ～254 Ma).Different types of Permian igneous rocks are identified by Sr-Nd-Pb-Hf-Mg isotopes,including arc-featured rocks derived from the metasomatic lithospheric mantle and tholeiite related to ocean ridges subduction and slab window.Together with contemporaneous A-type granite,these rocks reveal that the western margin of Khanka Massif was under subduction of ocean ridges tectonic setting in the Permian,further indicating the ongoing subduction of the eastern part of the Paleo-Asian Ocean.3.Zircon U-Pb geochronology shows that Triassic magmatism in central-southern Jilin can be divided into early Middle Triassic(246 Ma)and Late Triassic(219-220 Ma).Middle Triassic trachyandesites in southern Jilin Province were solely generated through partial melting of the ancient lower crust of the NCC,implying ongoing southward subduction of the Paleo-Asian Ocean Plate beneath the NCC at this time.Late Triassic igneous rocks are distributed east-west on both sides of the NCC suture zone.The Late Triassic trachyandesites in southern Jilin Province were likely generated through mixing between magmas generated through partial melting of NCC lithospheric mantle and juvenile eastern CAOB crust.The Late Triassic intrusive rocks in the central Jilin Province area have bimodal characteristics,indicating that the area was in a post-orogenic extensional setting during the Late Triassic.The above findings jointly suggest that the Paleo-Asian Ocean closed during a late stage of the Middle Triassic.In summary,the tectonic system of the Paleo-Asian Ocean during Early Permian-Middle Triassic period has not yet ended,and the final closure of the Paleo-Asian Ocean at the end of the Middle Triassic.Moreover,this area was under an extension tectonic setting after the closure of the Paleo-Asian Ocean during the Late Triassic.Second,the Sr-Nd-Pb-Hf-Mg-Ba isotopes were used to constrain the mantle source properties of typical mantle-derived igneous rocks along the northern margin of NCC from Late Permian to Late Triassic,revealing the temporal and spatial variation of the source properties.The contribution from the Paleo-Asian Ocean to mantle modification by different fluids or melts during the Permian-Triassic period was also revealed.1.The systematic study of Sr-Nd-Pb-Hf-Mg-Ba isotopes of mantle-derived igneous rocks in the eastern part of the northern margin of the NCC reveals that the mantle properties of the Late Paleozoic-Early Mesozoic are heterogeneous in time and space.The Late Permian appinite in the Fuxin area shows that the lithospheric mantle is mainly modified by serpentine fluid.The Late Permian-Early Trassic mantle-derived magma in the Kaiyuan area shows that its lithospheric mantle is primarily modified by ocean crust fluid and sediment melt.The monzodiorite and hornblendite in the Late Permian in the Faku area indicate that bulk sediments and serpentine components diapir into the lithosphere mantle.The magma source of the Mayihe pluton in Linjiang in the Late Triassic is the asthenosphere mantle replaced by a small amount of sediment melt.2.The influence of the southern subduction of the Paleo-Asian Ocean during the Permian-Triassic on the mantle properties of the northern margin of the North China Craton is mainly from different fluid metasomatic processes.Together with previous studies,it is suggested that the spatial differences in the temperature structure of the subduction zone during the evolution and final closure of the Paleo-Asian Ocean are likely responsible for the differences in the metasomatism process.